Chapter 16 Replication

If binary logging is disabled (log_bin is OFF), or if log_slave_updates is disabled, the server stores the GTID belonging to each transaction together with the transaction in the table. In addition, the table is compressed periodically at a user-configurable rate; see mysql.gtid_executed Table Compression, for more information. This situation can only apply on a replica where binary logging or replica update logging is disabled. It does not apply on a replication source server, because on the source, binary logging must be enabled for replication to take place.

If binary logging is enabled (log_bin is ON), whenever the binary log is rotated or the server is shut down, the server writes GTIDs for all transactions that were written into the previous binary log into the mysql.gtid_executed table. This situation applies on a replication source server, or a replica where binary logging is enabled.

In the event of the server stopping unexpectedly, the set of GTIDs from the current binary log file is not saved in the mysql.gtid_executed table. These GTIDs are added to the table from the binary log file during recovery. The exception to this is if binary logging is not enabled when the server is restarted. In this situation, the server cannot access the binary log file to recover the GTIDs, so replication cannot be started.

When binary logging is enabled, the mysql.gtid_executed table does not hold a complete record of the GTIDs for all executed transactions. That information is provided by the global value of the gtid_executed system variable. Always use @@GLOBAL.gtid_executed, which is updated after every commit, to represent the GTID state for the MySQL server, and do not query the mysql.gtid_executed table.

A stored procedure is invoked that commits multiple transactions. One GTID is generated for each transaction that the procedure commits.

A multi-table DROP TABLE statement drops tables of different types.

A CREATE TABLE ... SELECT statement is issued when row-based replication is in use (binlog_format=ROW). One GTID is generated for the CREATE TABLE action and one GTID is generated for the row-insert actions.

When gtid_next is set to AUTOMATIC, which is the default, and a transaction is committed and written to the binary log, the server automatically generates and assigns a new GTID. If a transaction is rolled back or not written to the binary log for another reason, the server does not generate and assign a GTID.

If you set gtid_next to a valid GTID (consisting of a UUID and a transaction sequence number, separated by a colon), the server assigns that GTID to your transaction. This GTID is assigned and added to gtid_executed even when the transaction is not written to the binary log, or when the transaction is empty.

GTIDs of replicated transactions that were committed with binary logging disabled on the replica.

GTIDs of transactions that were written to a binary log file that has now been purged.

GTIDs that were added explicitly to the set by the statement SET @@GLOBAL.gtid_purged.

gtid_executed is computed as the union of the GTIDs in Previous_gtids_log_event in the most recent binary log file, the GTIDs of transactions in that binary log file, and the GTIDs stored in the mysql.gtid_executed table. This GTID set contains all the GTIDs that have been used (or added explicitly to gtid_purged) on the server, whether or not they are currently in a binary log file on the server. It does not include the GTIDs for transactions that are currently being processed on the server (@@GLOBAL.gtid_owned).

gtid_purged is computed by first adding the GTIDs in Previous_gtids_log_event in the most recent binary log file and the GTIDs of transactions in that binary log file. This step gives the set of GTIDs that are currently, or were once, recorded in a binary log on the server (gtids_in_binlog). Next, the GTIDs in Previous_gtids_log_event in the oldest binary log file are subtracted from gtids_in_binlog. This step gives the set of GTIDs that are currently recorded in a binary log on the server (gtids_in_binlog_not_purged). Finally, gtids_in_binlog_not_purged is subtracted from gtid_executed. The result is the set of GTIDs that have been used on the server, but are not currently recorded in a binary log file on the server, and this result is used to initialize gtid_purged.

The value of the gtid_purged system variable is set to an empty string ('').

The global value (but not the session value) of the gtid_executed system variable is set to an empty string.

The mysql.gtid_executed table is cleared (see mysql.gtid_executed Table).

If the server has binary logging enabled, the existing binary log files are deleted and the binary log index file is cleared.

abort-slave-event-count: Option used by mysql-test for debugging and testing of replication.

auto_increment_increment: AUTO_INCREMENT columns are incremented by this value.

auto_increment_offset: Offset added to AUTO_INCREMENT columns.

binlog_gtid_simple_recovery: Controls how binary logs are iterated during GTID recovery.

Com_change_master: Count of CHANGE MASTER TO statements.

Com_show_master_status: Count of SHOW MASTER STATUS statements.

Com_show_slave_hosts: Count of SHOW REPLICAS and SHOW SLAVE HOSTS statements.

Com_show_slave_status: Count of SHOW REPLICA STATUS and SHOW SLAVE STATUS statements.

Com_slave_start: Count of START REPLICA and START SLAVE statements.

Com_slave_stop: Count of STOP REPLICA and STOP SLAVE statements.

disconnect-slave-event-count: Option used by mysql-test for debugging and testing of replication.

enforce_gtid_consistency: Prevents execution of statements that cannot be logged in transactionally safe manner.

expire_logs_days: Purge binary logs after this many days.

gtid_executed: Global: All GTIDs in binary log (global) or current transaction (session). Read-only.

gtid_executed_compression_period: Compress gtid_executed table each time this many transactions have occurred. 0 means never compress this table. Applies only when binary logging is disabled.

gtid_mode: Controls whether GTID based logging is enabled and what type of transactions logs can contain.

gtid_next: Specifies GTID for next statement to execute; see documentation for details.

gtid_owned: Set of GTIDs owned by this client (session), or by all clients, together with thread ID of owner (global). Read-only.

gtid_purged: Set of all GTIDs that have been purged from binary log.

init_slave: Statements that are executed when replica connects to source.

log_bin_trust_function_creators: If equal to 0 (default), then when --log-bin is used, stored function creation is allowed only to users having SUPER privilege and only if function created does not break binary logging.

log_builtin_as_identified_by_password: Whether to log CREATE/ALTER USER, GRANT in backward-compatible fashion.

log_statements_unsafe_for_binlog: Disables error 1592 warnings being written to error log.

master-info-file: Location and name of file that remembers source and where I/O replication thread is in source's binary log.

master-retry-count: Number of tries replica makes to connect to source before giving up.

master_info_repository: Whether to write connection metadata repository, containing source information and replication I/O thread location in source's binary log, to file or table.

max_relay_log_size: If nonzero, relay log is rotated automatically when its size exceeds this value. If zero, size at which rotation occurs is determined by value of max_binlog_size.

relay_log: Location and base name to use for relay logs.

relay_log_basename: Complete path to relay log, including file name.

relay_log_index: Location and name to use for file that keeps list of last relay logs.

relay_log_info_file: File name for applier metadata repository in which replica records information about relay logs.

relay_log_info_repository: Whether to write location of replication SQL thread in relay logs to file or table.

relay_log_purge: Determines whether relay logs are purged.

relay_log_recovery: Whether automatic recovery of relay log files from source at startup is enabled; must be enabled for crash-safe replica.

relay_log_space_limit: Maximum space to use for all relay logs.

replicate-do-db: Tells replication SQL thread to restrict replication to specified database.

replicate-do-table: Tells replication SQL thread to restrict replication to specified table.

replicate-ignore-db: Tells replication SQL thread not to replicate to specified database.

replicate-ignore-table: Tells replication SQL thread not to replicate to specified table.

replicate-rewrite-db: Updates to database with different name from original.

replicate-same-server-id: In replication, if enabled, do not skip events having our server id.

replicate-wild-do-table: Tells replication SQL thread to restrict replication to tables that match specified wildcard pattern.

replicate-wild-ignore-table: Tells replication SQL thread not to replicate to tables that match given wildcard pattern.

report_host: Host name or IP of replica to be reported to source during replica registration.

report_password: Arbitrary password which replica server should report to source; not same as password for replication user account.

report_port: Port for connecting to replica reported to source during replica registration.

report_user: Arbitrary user name which replica server should report to source; not same as name used for replication user account.

Rpl_semi_sync_master_clients: Number of semisynchronous replicas.

rpl_semi_sync_master_enabled: Whether semisynchronous replication is enabled on source.

Rpl_semi_sync_master_net_avg_wait_time: Average time source has waited for replies from replica.

Rpl_semi_sync_master_net_wait_time: Total time source has waited for replies from replica.

Rpl_semi_sync_master_net_waits: Total number of times source waited for replies from replica.

Rpl_semi_sync_master_no_times: Number of times source turned off semisynchronous replication.

Rpl_semi_sync_master_no_tx: Number of commits not acknowledged successfully.

Rpl_semi_sync_master_status: Whether semisynchronous replication is operational on source.

Rpl_semi_sync_master_timefunc_failures: Number of times source failed when calling time functions.

rpl_semi_sync_master_timeout: Number of milliseconds to wait for replica acknowledgment.

rpl_semi_sync_master_trace_level: Semisynchronous replication debug trace level on source.

Rpl_semi_sync_master_tx_avg_wait_time: Average time source waited for each transaction.

Rpl_semi_sync_master_tx_wait_time: Total time source waited for transactions.

Rpl_semi_sync_master_tx_waits: Total number of times source waited for transactions.

rpl_semi_sync_master_wait_for_slave_count: Number of replica acknowledgments source must receive per transaction before proceeding.

rpl_semi_sync_master_wait_no_slave: Whether source waits for timeout even with no replicas.

rpl_semi_sync_master_wait_point: Wait point for replica transaction receipt acknowledgment.

Rpl_semi_sync_master_wait_pos_backtraverse: Total number of times source has waited for event with binary coordinates lower than events waited for previously.

Rpl_semi_sync_master_wait_sessions: Number of sessions currently waiting for replica replies.

Rpl_semi_sync_master_yes_tx: Number of commits acknowledged successfully.

rpl_semi_sync_slave_enabled: Whether semisynchronous replication is enabled on replica.

Rpl_semi_sync_slave_status: Whether semisynchronous replication is operational on replica.

rpl_semi_sync_slave_trace_level: Semisynchronous replication debug trace level on replica.

rpl_stop_slave_timeout: Number of seconds that STOP REPLICA or STOP SLAVE waits before timing out.

server_uuid: Server's globally unique ID, automatically (re)generated at server start.

show-slave-auth-info: Show user name and password in SHOW REPLICAS and SHOW SLAVE HOSTS on this source.

skip-slave-start: If set, replication is not autostarted when replica server starts.

slave_load_tmpdir: Location where replica should put its temporary files when replicating LOAD DATA statements.

slave_net_timeout: Number of seconds to wait for more data from source/replica connection before aborting read.

slave-skip-errors: Tells replication thread to continue replication when query returns error from provided list.

slave_checkpoint_group: Maximum number of transactions processed by multithreaded replica before checkpoint operation is called to update progress status. Not supported by NDB Cluster.

slave_checkpoint_period: Update progress status of multithreaded replica and flush relay log info to disk after this number of milliseconds. Not supported by NDB Cluster.

slave_compressed_protocol: Use compression of source/replica protocol.

slave_exec_mode: Allows for switching replication thread between IDEMPOTENT mode (key and some other errors suppressed) and STRICT mode; STRICT mode is default, except for NDB Cluster, where IDEMPOTENT is always used.

Slave_heartbeat_period: Replica's replication heartbeat interval, in seconds.

Slave_last_heartbeat: Shows when latest heartbeat signal was received, in TIMESTAMP format.

slave_max_allowed_packet: Maximum size, in bytes, of packet that can be sent from replication source server to replica; overrides max_allowed_packet.

Slave_open_temp_tables: Number of temporary tables that replication SQL thread currently has open.

slave_parallel_type: Tells replica to use timestamp information (LOGICAL_CLOCK) or database partioning (DATABASE) to parallelize transactions.

slave_parallel_workers: Number of applier threads for executing replication transactions in parallel. 0 disables replica multithreading. Not supported by MySQL Cluster.

slave_pending_jobs_size_max: Maximum size of replica worker queues holding events not yet applied.

slave_preserve_commit_order: Ensures that all commits by replica workers happen in same order as on source to maintain consistency when using parallel applier threads.

Slave_received_heartbeats: Number of heartbeats received by replica since previous reset.

Slave_retried_transactions: Total number of times since startup that replication SQL thread has retried transactions.

slave_rows_search_algorithms: Determines search algorithms used for replica update batching. Any 2 or 3 from this list: INDEX_SEARCH, TABLE_SCAN, HASH_SCAN.

Slave_rows_last_search_algorithm_used: Search algorithm most recently used by this replica to locate rows for row-based replication (index, table, or hash scan).

Slave_running: State of this server as replica (replication I/O thread status).

slave_transaction_retries: Number of times replication SQL thread retries transaction in case it failed with deadlock or elapsed lock wait timeout, before giving up and stopping.

slave_type_conversions: Controls type conversion mode on replica. Value is list of zero or more elements from this list: ALL_LOSSY, ALL_NON_LOSSY. Set to empty string to disallow type conversions between source and replica.

sql_log_bin: Controls binary logging for current session.

sql_slave_skip_counter: Number of events from source that replica should skip. Not compatible with GTID replication.

sync_master_info: Synchronize master.info to disk after every #th event.

sync_relay_log: Synchronize relay log to disk after every #th event.

sync_relay_log_info: Synchronize relay.info file to disk after every #th event.

transaction_write_set_extraction: Defines algorithm used to hash writes extracted during transaction.

binlog-checksum: Enable/disable binary log checksums.

binlog-do-db: Limits binary logging to specific databases.

binlog_format: Specifies format of binary log.

binlog-ignore-db: Tells source that updates to given database should not be written to binary log.

binlog-row-event-max-size: Binary log max event size.

Binlog_cache_disk_use: Number of transactions which used temporary file instead of binary log cache.

binlog_cache_size: Size of cache to hold SQL statements for binary log during transaction.

Binlog_cache_use: Number of transactions that used temporary binary log cache.

binlog_checksum: Enable/disable binary log checksums.

binlog_direct_non_transactional_updates: Causes updates using statement format to nontransactional engines to be written directly to binary log. See documentation before using.

binlog_error_action: Controls what happens when server cannot write to binary log.

binlog_group_commit_sync_delay: Sets number of microseconds to wait before synchronizing transactions to disk.

binlog_group_commit_sync_no_delay_count: Sets maximum number of transactions to wait for before aborting current delay specified by binlog_group_commit_sync_delay.

binlog_max_flush_queue_time: How long to read transactions before flushing to binary log.

binlog_order_commits: Whether to commit in same order as writes to binary log.

binlog_row_image: Use full or minimal images when logging row changes.

binlog_rows_query_log_events: When enabled, enables logging of rows query log events when using row-based logging. Disabled by default. Do not enable when producing logs for pre-5.6 replicas/readers.

Binlog_stmt_cache_disk_use: Number of nontransactional statements that used temporary file instead of binary log statement cache.

binlog_stmt_cache_size: Size of cache to hold nontransactional statements for binary log during transaction.

Binlog_stmt_cache_use: Number of statements that used temporary binary log statement cache.

binlog_transaction_dependency_tracking: Source of dependency information (commit timestamps or transaction write sets) from which to assess which transactions can be executed in parallel by replica's multithreaded applier.

binlog_transaction_dependency_history_size: Number of row hashes kept for looking up transaction that last updated some row.

Com_show_binlog_events: Count of SHOW BINLOG EVENTS statements.

Com_show_binlogs: Count of SHOW BINLOGS statements.

log-bin: Base name for binary log files.

log-bin-index: Name of binary log index file.

log_bin: Whether binary log is enabled.

log_bin_basename: Path and base name for binary log files.

log_bin_use_v1_row_events: Whether server is using version 1 binary log row events.

log_slave_updates: Whether replica should log updates performed by its replication SQL thread to its own binary log.

master_verify_checksum: Cause source to examine checksums when reading from binary log.

max-binlog-dump-events: Option used by mysql-test for debugging and testing of replication.

max_binlog_cache_size: Can be used to restrict total size used to cache multi-statement transaction.

max_binlog_size: Binary log is rotated automatically when size exceeds this value.

max_binlog_stmt_cache_size: Can be used to restrict total size used to cache all nontransactional statements during transaction.

slave-sql-verify-checksum: Cause replica to examine checksums when reading from relay log.

slave_sql_verify_checksum: Cause replica to examine checksums when reading from relay log.

sporadic-binlog-dump-fail: Option used by mysql-test for debugging and testing of replication.

sync_binlog: Synchronously flush binary log to disk after every #th event.

--show-slave-auth-info

Display replica user names and passwords in the output of SHOW SLAVE HOSTS on the source server for replicas started with the --report-user and --report-password options.

auto_increment_increment

auto_increment_increment and auto_increment_offset are intended for use with source-to-source replication, and can be used to control the operation of AUTO_INCREMENT columns. Both variables have global and session values, and each can assume an integer value between 1 and 65,535 inclusive. Setting the value of either of these two variables to 0 causes its value to be set to 1 instead. Attempting to set the value of either of these two variables to an integer greater than 65,535 or less than 0 causes its value to be set to 65,535 instead. Attempting to set the value of auto_increment_increment or auto_increment_offset to a noninteger value produces an error, and the actual value of the variable remains unchanged.

When Group Replication is started on a server, the value of auto_increment_increment is changed to the value of group_replication_auto_increment_increment, which defaults to 7, and the value of auto_increment_offset is changed to the server ID. The changes are reverted when Group Replication is stopped. These changes are only made and reverted if auto_increment_increment and auto_increment_offset each have their default value of 1. If their values have already been modified from the default, Group Replication does not alter them.

auto_increment_increment and auto_increment_offset affect AUTO_INCREMENT column behavior as follows:

If either of these variables is changed, and then new rows inserted into a table containing an AUTO_INCREMENT column, the results may seem counterintuitive because the series of AUTO_INCREMENT values is calculated without regard to any values already present in the column, and the next value inserted is the least value in the series that is greater than the maximum existing value in the AUTO_INCREMENT column. The series is calculated like this:

auto_increment_offset + N × auto_increment_increment

where N is a positive integer value in the series [1, 2, 3, ...]. For example:

mysql> SHOW VARIABLES LIKE 'auto_inc%';
+--------------------------+-------+
| Variable_name            | Value |
+--------------------------+-------+
| auto_increment_increment | 10    |
| auto_increment_offset    | 5     |
+--------------------------+-------+
2 rows in set (0.00 sec)

mysql> SELECT col FROM autoinc1;
+-----+
| col |
+-----+
|   1 |
|  11 |
|  21 |
|  31 |
+-----+
4 rows in set (0.00 sec)

mysql> INSERT INTO autoinc1 VALUES (NULL), (NULL), (NULL), (NULL);
Query OK, 4 rows affected (0.00 sec)
Records: 4  Duplicates: 0  Warnings: 0

mysql> SELECT col FROM autoinc1;
+-----+
| col |
+-----+
|   1 |
|  11 |
|  21 |
|  31 |
|  35 |
|  45 |
|  55 |
|  65 |
+-----+
8 rows in set (0.00 sec)

The values shown for auto_increment_increment and auto_increment_offset generate the series 5 + N × 10, that is, [5, 15, 25, 35, 45, ...]. The highest value present in the col column prior to the INSERT is 31, and the next available value in the AUTO_INCREMENT series is 35, so the inserted values for col begin at that point and the results are as shown for the SELECT query.

It is not possible to restrict the effects of these two variables to a single table; these variables control the behavior of all AUTO_INCREMENT columns in all tables on the MySQL server. If the global value of either variable is set, its effects persist until the global value is changed or overridden by setting the session value, or until mysqld is restarted. If the local value is set, the new value affects AUTO_INCREMENT columns for all tables into which new rows are inserted by the current user for the duration of the session, unless the values are changed during that session.

The default value of auto_increment_increment is 1. See Section 16.4.1.1, “Replication and AUTO_INCREMENT”.

auto_increment_offset

This variable has a default value of 1. If it is left with its default value, and Group Replication is started on the server, it is changed to the server ID. For more information, see the description for auto_increment_increment.

rpl_semi_sync_master_enabled

Controls whether semisynchronous replication is enabled on the source. To enable or disable the plugin, set this variable to ON or OFF (or 1 or 0), respectively. The default is OFF.

This variable is available only if the source-side semisynchronous replication plugin is installed.

rpl_semi_sync_master_timeout

A value in milliseconds that controls how long the source waits on a commit for acknowledgment from a replica before timing out and reverting to asynchronous replication. The default value is 10000 (10 seconds).

This variable is available only if the source-side semisynchronous replication plugin is installed.

rpl_semi_sync_master_trace_level

The semisynchronous replication debug trace level on the source. Four levels are defined:

This variable is available only if the source-side semisynchronous replication plugin is installed.

rpl_semi_sync_master_wait_for_slave_count

The number of replica acknowledgments the source must receive per transaction before proceeding. By default rpl_semi_sync_master_wait_for_slave_count is 1, meaning that semisynchronous replication proceeds after receiving a single replica acknowledgment. Performance is best for small values of this variable.

For example, if rpl_semi_sync_master_wait_for_slave_count is 2, then 2 replicas must acknowledge receipt of the transaction before the timeout period configured by rpl_semi_sync_master_timeout for semisynchronous replication to proceed. If fewer replicas acknowledge receipt of the transaction during the timeout period, the source reverts to normal replication.

This variable is available only if the source-side semisynchronous replication plugin is installed.

rpl_semi_sync_master_wait_no_slave

Controls whether the source waits for the timeout period configured by rpl_semi_sync_master_timeout to expire, even if the replica count drops to less than the number of replicas configured by rpl_semi_sync_master_wait_for_slave_count during the timeout period.

When the value of rpl_semi_sync_master_wait_no_slave is ON (the default), it is permissible for the replica count to drop to less than rpl_semi_sync_master_wait_for_slave_count during the timeout period. As long as enough replicas acknowledge the transaction before the timeout period expires, semisynchronous replication continues.

When the value of rpl_semi_sync_master_wait_no_slave is OFF, if the replica count drops to less than the number configured in rpl_semi_sync_master_wait_for_slave_count at any time during the timeout period configured by rpl_semi_sync_master_timeout, the source reverts to normal replication.

This variable is available only if the source-side semisynchronous replication plugin is installed.

rpl_semi_sync_master_wait_point

This variable controls the point at which a semisynchronous source waits for replica acknowledgment of transaction receipt before returning a status to the client that committed the transaction. These values are permitted:

The replication characteristics of these settings differ as follows:

This variable is available only if the source-side semisynchronous replication plugin is installed.

rpl_semi_sync_master_wait_point was added in MySQL 5.7.2. For older versions, semisynchronous source behavior is equivalent to a setting of AFTER_COMMIT.

This change introduces a version compatibility constraint because it increments the semisynchronous interface version: Servers for MySQL 5.7.2 and up do not work with semisynchronous replication plugins from older versions, nor do servers from older versions work with semisynchronous replication plugins for MySQL 5.7.2 and up.

--log-warnings[=level]

Causes the server to record more messages to the error log about what it is doing. With respect to replication, the server generates warnings that it succeeded in reconnecting after a network or connection failure, and provides information about how each replication thread started. This variable is set to 2 by default. To disable it, set it to 0. The server logs messages about statements that are unsafe for statement-based logging if the value is greater than 0. Aborted connections and access-denied errors for new connection attempts are logged if the value is greater than 1. See Section B.3.2.9, “Communication Errors and Aborted Connections”.

--master-info-file=file_name

The name to use for the file in which the replica records information about the source. The default name is master.info in the data directory. For information about the format of this file, see Section 16.2.4.2, “Replication Metadata Repositories”.

--master-retry-count=count

The number of times that the replica tries to reconnect to the source before giving up. The default value is 86400 times. A value of 0 means “infinite”, and the replica attempts to connect forever. Reconnection attempts are triggered when the replica reaches its connection timeout (specified by the slave_net_timeout system variable) without receiving data or a heartbeat signal from the source. Reconnection is attempted at intervals set by the MASTER_CONNECT_RETRY option of the CHANGE MASTER TO statement (which defaults to every 60 seconds).

This option is deprecated; expect it to be removed in a future MySQL release. Use the MASTER_RETRY_COUNT option of the CHANGE MASTER TO statement instead.

--max-relay-log-size=size

The size at which the server rotates relay log files automatically. If this value is nonzero, the relay log is rotated automatically when its size exceeds this value. If this value is zero (the default), the size at which relay log rotation occurs is determined by the value of max_binlog_size. For more information, see Section 16.2.4.1, “The Relay Log”.

--relay-log-purge={0|1}

Disable or enable automatic purging of relay logs as soon as they are no longer needed. The default value is 1 (enabled). This is a global variable that can be changed dynamically with SET GLOBAL relay_log_purge = N. Disabling purging of relay logs when enabling the --relay-log-recovery option puts data consistency at risk.

--relay-log-space-limit=size

This option places an upper limit on the total size in bytes of all relay logs on the replica. A value of 0 means “no limit”. This is useful for a replica server host that has limited disk space. When the limit is reached, the replication I/O thread stops reading binary log events from the source until the replication SQL thread has caught up and deleted some unused relay logs. Note that this limit is not absolute: There are cases where the SQL thread needs more events before it can delete relay logs. In that case, the I/O thread exceeds the limit until it becomes possible for the SQL thread to delete some relay logs because not doing so would cause a deadlock. You should not set --relay-log-space-limit to less than twice the value of --max-relay-log-size (or --max-binlog-size if --max-relay-log-size is 0). In that case, there is a chance that the I/O thread waits for free space because --relay-log-space-limit is exceeded, but the SQL thread has no relay log to purge and is unable to satisfy the I/O thread. This forces the I/O thread to ignore --relay-log-space-limit temporarily.

--replicate-do-db=db_name

Creates a replication filter using the name of a database. Such filters can also be created using CHANGE REPLICATION FILTER REPLICATE_DO_DB. The precise effect of this filtering depends on whether statement-based or row-based replication is in use, and are described in the next several paragraphs.

Statement-based replication.  Tell the replication SQL thread to restrict replication to statements where the default database (that is, the one selected by USE) is db_name. To specify more than one database, use this option multiple times, once for each database; however, doing so does not replicate cross-database statements such as UPDATE some_db.some_table SET foo='bar' while a different database (or no database) is selected.

An example of what does not work as you might expect when using statement-based replication: If the replica is started with --replicate-do-db=sales and you issue the following statements on the source, the UPDATE statement is not replicated:

USE prices;
UPDATE sales.january SET amount=amount+1000;

The main reason for this “check just the default database” behavior is that it is difficult from the statement alone to know whether it should be replicated (for example, if you are using multiple-table DELETE statements or multiple-table UPDATE statements that act across multiple databases). It is also faster to check only the default database rather than all databases if there is no need.

Row-based replication.  Tells the replication SQL thread to restrict replication to database db_name. Only tables belonging to db_name are changed; the current database has no effect on this. Suppose that the replica is started with --replicate-do-db=sales and row-based replication is in effect, and then the following statements are run on the source:

USE prices;
UPDATE sales.february SET amount=amount+100;

The february table in the sales database on the replica is changed in accordance with the UPDATE statement; this occurs whether or not the USE statement was issued. However, issuing the following statements on the source has no effect on the replica when using row-based replication and --replicate-do-db=sales:

USE prices;
UPDATE prices.march SET amount=amount-25;

Even if the statement USE prices were changed to USE sales, the UPDATE statement's effects would still not be replicated.

Another important difference in how --replicate-do-db is handled in statement-based replication as opposed to row-based replication occurs with regard to statements that refer to multiple databases. Suppose that the replica is started with --replicate-do-db=db1, and the following statements are executed on the source:

USE db1;
UPDATE db1.table1, db2.table2 SET db1.table1.col1 = 10, db2.table2.col2 = 20;

If you are using statement-based replication, then both tables are updated on the replica. However, when using row-based replication, only table1 is affected on the replica; since table2 is in a different database, table2 on the replica is not changed by the UPDATE. Now suppose that, instead of the USE db1 statement, a USE db4 statement had been used:

USE db4;
UPDATE db1.table1, db2.table2 SET db1.table1.col1 = 10, db2.table2.col2 = 20;

In this case, the UPDATE statement would have no effect on the replica when using statement-based replication. However, if you are using row-based replication, the UPDATE would change table1 on the replica, but not table2—in other words, only tables in the database named by --replicate-do-db are changed, and the choice of default database has no effect on this behavior.

If you need cross-database updates to work, use --replicate-wild-do-table=db_name.% instead. See Section 16.2.5, “How Servers Evaluate Replication Filtering Rules”.

--replicate-ignore-db=db_name

Creates a replication filter using the name of a database. Such filters can also be created using CHANGE REPLICATION FILTER REPLICATE_IGNORE_DB. As with --replicate-do-db, the precise effect of this filtering depends on whether statement-based or row-based replication is in use, and are described in the next several paragraphs.

Statement-based replication.  Tells the replication SQL thread not to replicate any statement where the default database (that is, the one selected by USE) is db_name.

Row-based replication.  Tells the replication SQL thread not to update any tables in the database db_name. The default database has no effect.

When using statement-based replication, the following example does not work as you might expect. Suppose that the replica is started with --replicate-ignore-db=sales and you issue the following statements on the source:

USE prices;
UPDATE sales.january SET amount=amount+1000;

The UPDATE statement is replicated in such a case because --replicate-ignore-db applies only to the default database (determined by the USE statement). Because the sales database was specified explicitly in the statement, the statement has not been filtered. However, when using row-based replication, the UPDATE statement's effects are not propagated to the replica, and the replica's copy of the sales.january table is unchanged; in this instance, --replicate-ignore-db=sales causes all changes made to tables in the source's copy of the sales database to be ignored by the replica.

To specify more than one database to ignore, use this option multiple times, once for each database. Because database names can contain commas, if you supply a comma separated list then the list is treated as the name of a single database.

You should not use this option if you are using cross-database updates and you do not want these updates to be replicated. See Section 16.2.5, “How Servers Evaluate Replication Filtering Rules”.

If you need cross-database updates to work, use --replicate-wild-ignore-table=db_name.% instead. See Section 16.2.5, “How Servers Evaluate Replication Filtering Rules”.

--replicate-do-table=db_name.tbl_name

Creates a replication filter by telling the replication SQL thread to restrict replication to a given table. To specify more than one table, use this option multiple times, once for each table. This works for both cross-database updates and default database updates, in contrast to --replicate-do-db. See Section 16.2.5, “How Servers Evaluate Replication Filtering Rules”. You can also create such a filter by issuing a CHANGE REPLICATION FILTER REPLICATE_DO_TABLE statement.

This option affects only statements that apply to tables. It does not affect statements that apply only to other database objects, such as stored routines. To filter statements operating on stored routines, use one or more of the --replicate-*-db options.

--replicate-ignore-table=db_name.tbl_name

Creates a replication filter by telling the replication SQL thread not to replicate any statement that updates the specified table, even if any other tables might be updated by the same statement. To specify more than one table to ignore, use this option multiple times, once for each table. This works for cross-database updates, in contrast to --replicate-ignore-db. See Section 16.2.5, “How Servers Evaluate Replication Filtering Rules”. You can also create such a filter by issuing a CHANGE REPLICATION FILTER REPLICATE_IGNORE_TABLE statement.

This option affects only statements that apply to tables. It does not affect statements that apply only to other database objects, such as stored routines. To filter statements operating on stored routines, use one or more of the --replicate-*-db options.

--replicate-rewrite-db=from_name->to_name

Tells the replica to create a replication filter that translates the specified database to to_name if it was from_name on the source. Only statements involving tables are affected, not statements such as CREATE DATABASE, DROP DATABASE, and ALTER DATABASE.

To specify multiple rewrites, use this option multiple times. The server uses the first one with a from_name value that matches. The database name translation is done before the --replicate-* rules are tested. You can also create such a filter by issuing a CHANGE REPLICATION FILTER REPLICATE_REWRITE_DB statement.

If you use the --replicate-rewrite-db option on the command line and the > character is special to your command interpreter, quote the option value. For example:

shell> mysqld --replicate-rewrite-db="olddb->newdb"

The effect of the --replicate-rewrite-db option differs depending on whether statement-based or row-based binary logging format is used for the query. With statement-based format, DML statements are translated based on the current database, as specified by the USE statement. With row-based format, DML statements are translated based on the database where the modified table exists. DDL statements are always filtered based on the current database, as specified by the USE statement, regardless of the binary logging format.

To ensure that rewriting produces the expected results, particularly in combination with other replication filtering options, follow these recommendations when you use the --replicate-rewrite-db option:

If these recommendations are followed, it is safe to use the --replicate-rewrite-db option in combination with table-level replication filtering options such as --replicate-do-table.

--replicate-same-server-id

To be used on replica servers. Usually you should use the default setting of 0, to prevent infinite loops caused by circular replication. If set to 1, the replica does not skip events having its own server ID. Normally, this is useful only in rare configurations. Cannot be set to 1 if log_slave_updates is enabled. By default, the replication I/O thread does not write binary log events to the relay log if they have the replica's server ID (this optimization helps save disk usage). If you want to use --replicate-same-server-id, be sure to start the replica with this option before you make the replica read its own events that you want the replication SQL thread to execute.

--replicate-wild-do-table=db_name.tbl_name

Creates a replication filter by telling the replication SQL thread to restrict replication to statements where any of the updated tables match the specified database and table name patterns. Patterns can contain the % and _ wildcard characters, which have the same meaning as for the LIKE pattern-matching operator. To specify more than one table, use this option multiple times, once for each table. This works for cross-database updates. See Section 16.2.5, “How Servers Evaluate Replication Filtering Rules”. You can also create such a filter by issuing a CHANGE REPLICATION FILTER REPLICATE_WILD_DO_TABLE statement.

This option applies to tables, views, and triggers. It does not apply to stored procedures and functions, or events. To filter statements operating on the latter objects, use one or more of the --replicate-*-db options.

As an example, --replicate-wild-do-table=foo%.bar% replicates only updates that use a table where the database name starts with foo and the table name starts with bar.

If the table name pattern is %, it matches any table name and the option also applies to database-level statements (CREATE DATABASE, DROP DATABASE, and ALTER DATABASE). For example, if you use --replicate-wild-do-table=foo%.%, database-level statements are replicated if the database name matches the pattern foo%.

To include literal wildcard characters in the database or table name patterns, escape them with a backslash. For example, to replicate all tables of a database that is named my_own%db, but not replicate tables from the my1ownAABCdb database, you should escape the _ and % characters like this: --replicate-wild-do-table=my\_own\%db. If you use the option on the command line, you might need to double the backslashes or quote the option value, depending on your command interpreter. For example, with the bash shell, you would need to type --replicate-wild-do-table=my\\_own\\%db.

--replicate-wild-ignore-table=db_name.tbl_name

Creates a replication filter which keeps the replication SQL thread from replicating a statement in which any table matches the given wildcard pattern. To specify more than one table to ignore, use this option multiple times, once for each table. This works for cross-database updates. See Section 16.2.5, “How Servers Evaluate Replication Filtering Rules”. You can also create such a filter by issuing a CHANGE REPLICATION FILTER REPLICATE_WILD_IGNORE_TABLE statement.

As an example, --replicate-wild-ignore-table=foo%.bar% does not replicate updates that use a table where the database name starts with foo and the table name starts with bar.

For information about how matching works, see the description of the --replicate-wild-do-table option. The rules for including literal wildcard characters in the option value are the same as for --replicate-wild-ignore-table as well.

--skip-slave-start

Tells the replica server not to start the replication threads when the server starts. To start the threads later, use a START SLAVE statement.

--slave-skip-errors=[err_code1,err_code2,...|all|ddl_exist_errors]

Normally, replication stops when an error occurs on the replica, which gives you the opportunity to resolve the inconsistency in the data manually. This option causes the replication SQL thread to continue replication when a statement returns any of the errors listed in the option value.

Do not use this option unless you fully understand why you are getting errors. If there are no bugs in your replication setup and client programs, and no bugs in MySQL itself, an error that stops replication should never occur. Indiscriminate use of this option results in replicas becoming hopelessly out of synchrony with the source, with you having no idea why this has occurred.

For error codes, you should use the numbers provided by the error message in the replica's error log and in the output of SHOW SLAVE STATUS. Appendix B, Error Messages and Common Problems, lists server error codes.

The shorthand value ddl_exist_errors is equivalent to the error code list 1007,1008,1050,1051,1054,1060,1061,1068,1094,1146.

You can also (but should not) use the very nonrecommended value of all to cause the replica to ignore all error messages and keeps going regardless of what happens. Needless to say, if you use all, there are no guarantees regarding the integrity of your data. Please do not complain (or file bug reports) in this case if the replica's data is not anywhere close to what it is on the source. You have been warned.

Examples:

--slave-skip-errors=1062,1053
--slave-skip-errors=all
--slave-skip-errors=ddl_exist_errors

--slave-sql-verify-checksum={0|1}

When this option is enabled, the replica examines checksums read from the relay log,. In the event of a mismatch, the replica stops with an error.

--abort-slave-event-count

When this option is set to some positive integer value other than 0 (the default) it affects replication behavior as follows: After the replication SQL thread has started, value log events are permitted to be executed; after that, the replication SQL thread does not receive any more events, just as if the network connection from the source were cut. The replication SQL thread continues to run, and the output from SHOW SLAVE STATUS displays Yes in both the Slave_IO_Running and the Slave_SQL_Running columns, but no further events are read from the relay log.

--disconnect-slave-event-count

master_info_repository

relay_log_info_repository

init_slave

This variable is similar to init_connect, but is a string to be executed by a replica server each time the replication SQL thread starts. The format of the string is the same as for the init_connect variable. The setting of this variable takes effect for subsequent START SLAVE statements.

log_slow_slave_statements

When the slow query log is enabled, this variable enables logging for queries that have taken more than long_query_time seconds to execute on the replica. Note that if row-based replication is in use (binlog_format=ROW), log_slow_slave_statements has no effect. Queries are only added to the replica's slow query log when they are logged in statement format in the binary log, that is, when binlog_format=STATEMENT is set, or when binlog_format=MIXED is set and the statement is logged in statement format. Slow queries that are logged in row format when binlog_format=MIXED is set, or that are logged when binlog_format=ROW is set, are not added to the replica's slow query log, even if log_slow_slave_statements is enabled.

Setting log_slow_slave_statements has no immediate effect. The state of the variable applies on all subsequent START SLAVE statements. Also note that the global setting for long_query_time applies for the lifetime of the SQL thread. If you change that setting, you must stop and restart the replication SQL thread to implement the change there (for example, by issuing STOP SLAVE and START SLAVE statements with the SQL_THREAD option).

master_info_repository

The setting of this variable determines whether the replica records metadata about the source, consisting of status and connection information, to an InnoDB table in the mysql system database, or as a file in the data directory. For more information on the connection metadata repository, see Section 16.2.4, “Relay Log and Replication Metadata Repositories”.

The default setting is FILE. As a file, the replica's connection metadata repository is named master.info by default. You can change this name using the --master-info-file option.

The alternative setting is TABLE. As an InnoDB table, the replica's connection metadata repository is named mysql.slave_master_info. The TABLE setting is required when multiple replication channels are configured.

This variable must be set to TABLE before configuring multiple replication channels. If you are using multiple replication channels, you cannot set the value back to FILE.

The setting for the location of the connection metadata repository has a direct influence on the effect had by the setting of the sync_master_info system variable. You can change the setting only when no replication threads are executing.

max_relay_log_size

If a write by a replica to its relay log causes the current log file size to exceed the value of this variable, the replica rotates the relay logs (closes the current file and opens the next one). If max_relay_log_size is 0, the server uses max_binlog_size for both the binary log and the relay log. If max_relay_log_size is greater than 0, it constrains the size of the relay log, which enables you to have different sizes for the two logs. You must set max_relay_log_size to between 4096 bytes and 1GB (inclusive), or to 0. The default value is 0. See Section 16.2.3, “Replication Threads”.

relay_log

The base name for relay log files. For the default replication channel, the default base name for relay logs is host_name-relay-bin. For non-default replication channels, the default base name for relay logs is host_name-relay-bin-channel, where channel is the name of the replication channel recorded in this relay log.

The server writes the file in the data directory unless the base name is given with a leading absolute path name to specify a different directory. The server creates relay log files in sequence by adding a numeric suffix to the base name.

Due to the manner in which MySQL parses server options, if you specify this variable at server startup, you must supply a value; the default base name is used only if the option is not actually specified. If you specify the relay_log system variable at server startup without specifying a value, unexpected behavior is likely to result; this behavior depends on the other options used, the order in which they are specified, and whether they are specified on the command line or in an option file. For more information about how MySQL handles server options, see Section 4.2.2, “Specifying Program Options”.

If you specify this variable, the value specified is also used as the base name for the relay log index file. You can override this behavior by specifying a different relay log index file base name using the relay_log_index system variable.

When the server reads an entry from the index file, it checks whether the entry contains a relative path. If it does, the relative part of the path is replaced with the absolute path set using the relay_log system variable. An absolute path remains unchanged; in such a case, the index must be edited manually to enable the new path or paths to be used.

You may find the relay_log system variable useful in performing the following tasks:

You can obtain the relay log file name (and path) from the relay_log_basename system variable.

relay_log_basename

Holds the base name and complete path to the relay log file. The maximum variable length is 256. This variable is set by the server and is read only.

relay_log_index

The name for the relay log index file. The maximum variable length is 256. For the default replication channel, the default name is host_name-relay-bin.index. For non-default replication channels, the default name is host_name-relay-bin-channel.index, where channel is the name of the replication channel recorded in this relay log index.

The server writes the file in the data directory unless the name is given with a leading absolute path name to specify a different directory. name.

Due to the manner in which MySQL parses server options, if you specify this variable at server startup, you must supply a value; the default base name is used only if the option is not actually specified. If you specify the relay_log_index system variable at server startup without specifying a value, unexpected behavior is likely to result; this behavior depends on the other options used, the order in which they are specified, and whether they are specified on the command line or in an option file. For more information about how MySQL handles server options, see Section 4.2.2, “Specifying Program Options”.

relay_log_info_file

The name of the file in which the replica records information about the relay logs, when relay_log_info_repository=FILE. If relay_log_info_repository=TABLE, it is the file name that would be used in case the repository was changed to FILE). The default name is relay-log.info in the data directory. For information about the applier metadata repository, see Section 16.2.4.2, “Replication Metadata Repositories”.

relay_log_info_repository

The setting of this variable determines whether the replica server stores its applier metadata repository as an InnoDB table in the mysql system database, or as a file in the data directory. For more information on the applier metadata repository, see Section 16.2.4, “Relay Log and Replication Metadata Repositories”.

The default setting is FILE. As a file, the replica's applier metadata repository is named relay-log.info by default, and you can change this name using the relay_log_info_file system variable.

With the setting TABLE, as an InnoDB table, the replica's applier metadata repository is named mysql.slave_relay_log_info. The TABLE setting is required when multiple replication channels are configured. The TABLE setting for the replica's applier metadata repository is also required to make replication resilient to unexpected halts. See Section 16.3.2, “Handling an Unexpected Halt of a Replica” for more information.

This variable must be set to TABLE before configuring multiple replication channels. If you are using multiple replication channels then you cannot set the value back to FILE.

The setting for the location of the applier metadata repository has a direct influence on the effect had by the setting of the sync_relay_log_info system variable. You can change the setting only when no replication threads are executing.

relay_log_purge

Disables or enables automatic purging of relay log files as soon as they are not needed any more. The default value is 1 (ON).

relay_log_recovery

If enabled, this variable enables automatic relay log recovery immediately following server startup. The recovery process creates a new relay log file, initializes the SQL thread position to this new relay log, and initializes the I/O thread to the SQL thread position. Reading of the relay log from the source then continues.

This global variable is read-only at runtime. Its value can be set with the --relay-log-recovery option at replica server startup, which should be used following an unexpected halt of a replica to ensure that no possibly corrupted relay logs are processed, and must be used in order to guarantee a crash-safe replica. The default value is 0 (disabled). For information on the combination of settings on a replica that is most resilient to unexpected halts, see Section 16.3.2, “Handling an Unexpected Halt of a Replica”.

This variable also interacts with the relay_log_purge variable, which controls purging of logs when they are no longer needed. Enabling relay_log_recovery when relay_log_purge is disabled risks reading the relay log from files that were not purged, leading to data inconsistency.

For a multithreaded replica (where slave_parallel_workers is greater than 0), from MySQL 5.7.13, setting relay_log_recovery = ON automatically handles any inconsistencies and gaps in the sequence of transactions that have been executed from the relay log. These gaps can occur when file position based replication is in use. (For more details, see Section 16.4.1.32, “Replication and Transaction Inconsistencies”.) The relay log recovery process deals with gaps using the same method as the START SLAVE UNTIL SQL_AFTER_MTS_GAPS statement would. When the replica reaches a consistent gap-free state, the relay log recovery process goes on to fetch further transactions from the source beginning at the replication SQL thread position. In MySQL versions prior to MySQL 5.7.13, this process was not automatic and required starting the server with relay_log_recovery=0, starting the replica with START SLAVE UNTIL SQL_AFTER_MTS_GAPS to fix any transaction inconsistencies, and then restarting the replica with relay_log_recovery=1. When GTID-based replication is in use, this process is unnecessary, and from MySQL 5.7.28 a multithreaded replica automatically skips relay log recovery when MASTER_AUTO_POSITION is set to ON, so the setting for relay_log_recovery makes no difference.

relay_log_space_limit

The maximum amount of space to use for all relay logs.

report_host

The host name or IP address of the replica to be reported to the source during replica registration. This value appears in the output of SHOW SLAVE HOSTS on the source server. Leave the value unset if you do not want the replica to register itself with the source.

report_password

The replication user account password of the replica to be reported to the source during replica registration. This value appears in the output of SHOW SLAVE HOSTS on the source server if the source was started with --show-slave-auth-info.

Although the name of this variable might imply otherwise, report_password is not connected to the MySQL user privilege system and so is not necessarily (or even likely to be) the same as the password for the MySQL replication user account.

report_port

The TCP/IP port number for connecting to the replica, to be reported to the source during replica registration. Set this only if the replica is listening on a nondefault port or if you have a special tunnel from the source or other clients to the replica. If you are not sure, do not use this option.

The default value for this option is the port number actually used by the replica. This is also the default value displayed by SHOW SLAVE HOSTS.

report_user

The account user name of the replica to be reported to the source during replica registration. This value appears in the output of SHOW SLAVE HOSTS on the source server if the source was started with --show-slave-auth-info.

Although the name of this variable might imply otherwise, report_user is not connected to the MySQL user privilege system and so is not necessarily (or even likely to be) the same as the name of the MySQL replication user account.

rpl_semi_sync_slave_enabled

Controls whether semisynchronous replication is enabled on the replica. To enable or disable the plugin, set this variable to ON or OFF (or 1 or 0), respectively. The default is OFF.

This variable is available only if the replica-side semisynchronous replication plugin is installed.

rpl_semi_sync_slave_trace_level

The semisynchronous replication debug trace level on the replica. See rpl_semi_sync_master_trace_level for the permissible values.

This variable is available only if the replica-side semisynchronous replication plugin is installed.

rpl_stop_slave_timeout

You can control the length of time (in seconds) that STOP SLAVE waits before timing out by setting this variable. This can be used to avoid deadlocks between STOP SLAVE and other SQL statements using different client connections to the replica.

The maximum and default value of rpl_stop_slave_timeout is 31536000 seconds (1 year). The minimum is 2 seconds. Changes to this variable take effect for subsequent STOP SLAVE statements.

This variable affects only the client that issues a STOP SLAVE statement. When the timeout is reached, the issuing client returns an error message stating that the command execution is incomplete. The client then stops waiting for the replication threads to stop, but the replication threads continue to try to stop, and the STOP SLAVE instruction remains in effect. Once the replication threads are no longer busy, the STOP SLAVE statement is executed and the replica stops.

slave_checkpoint_group

Sets the maximum number of transactions that can be processed by a multithreaded replica before a checkpoint operation is called to update its status as shown by SHOW SLAVE STATUS. Setting this variable has no effect on replicas for which multithreading is not enabled. Setting this variable has no immediate effect. The state of the variable applies on all subsequent START SLAVE commands.

This variable works in combination with the slave_checkpoint_period system variable in such a way that, when either limit is exceeded, the checkpoint is executed and the counters tracking both the number of transactions and the time elapsed since the last checkpoint are reset.

The minimum allowed value for this variable is 32, unless the server was built using -DWITH_DEBUG, in which case the minimum value is 1. The effective value is always a multiple of 8; you can set it to a value that is not such a multiple, but the server rounds it down to the next lower multiple of 8 before storing the value. (Exception: No such rounding is performed by the debug server.) Regardless of how the server was built, the default value is 512, and the maximum allowed value is 524280.

slave_checkpoint_period

Sets the maximum time (in milliseconds) that is allowed to pass before a checkpoint operation is called to update the status of a multithreaded replica as shown by SHOW SLAVE STATUS. Setting this variable has no effect on replicas for which multithreading is not enabled. Setting this variable takes effect for all replication channels immediately, including running channels.

This variable works in combination with the slave_checkpoint_group system variable in such a way that, when either limit is exceeded, the checkpoint is executed and the counters tracking both the number of transactions and the time elapsed since the last checkpoint are reset.

The minimum allowed value for this variable is 1, unless the server was built using -DWITH_DEBUG, in which case the minimum value is 0. Regardless of how the server was built, the default value is 300, and the maximum possible value is 4294967296 (4GB).

slave_compressed_protocol

Whether to use compression of the source/replica protocol if both source and replica support it. If this variable is disabled (the default), connections are uncompressed. Changes to this variable take effect on subsequent connection attempts; this includes after issuing a START SLAVE statement, as well as reconnections made by a running replication I/O thread (for example, after setting the MASTER_RETRY_COUNT option for the CHANGE MASTER TO statement). See also Section 4.2.6, “Connection Compression Control”.

slave_exec_mode

Controls how a replication thread resolves conflicts and errors during replication. IDEMPOTENT mode causes suppression of duplicate-key and no-key-found errors; STRICT means no such suppression takes place.

IDEMPOTENT mode is intended for use in multi-source replication, circular replication, and some other special replication scenarios for NDB Cluster Replication. (See Section 20.6.10, “NDB Cluster Replication: Bidrectional and Circular Replication”, and Section 20.6.11, “NDB Cluster Replication Conflict Resolution”, for more information.) NDB Cluster ignores any value explicitly set for slave_exec_mode, and always treats it as IDEMPOTENT.

In MySQL Server 5.7, STRICT mode is the default value.

For storage engines other than NDB, IDEMPOTENT mode should be used only when you are absolutely sure that duplicate-key errors and key-not-found errors can safely be ignored. It is meant to be used in fail-over scenarios for NDB Cluster where multi-source replication or circular replication is employed, and is not recommended for use in other cases.

slave_load_tmpdir

The name of the directory where the replica creates temporary files. Setting this variable takes effect for all replication channels immediately, including running channels. The variable value is by default equal to the value of the tmpdir system variable, or the default that applies when that system variable is not specified.

When the replication SQL thread replicates a LOAD DATA statement, it extracts the file to be loaded from the relay log into temporary files, and then loads these into the table. If the file loaded on the source is huge, the temporary files on the replica are huge, too. Therefore, it might be advisable to use this option to tell the replica to put temporary files in a directory located in some file system that has a lot of available space. In that case, the relay logs are huge as well, so you might also want to set the relay_log system variable to place the relay logs in that file system.

The directory specified by this option should be located in a disk-based file system (not a memory-based file system) so that the temporary files used to replicate LOAD DATA statements can survive machine restarts. The directory also should not be one that is cleared by the operating system during the system startup process. However, replication can now continue after a restart if the temporary files have been removed.

slave_max_allowed_packet

This variable sets the maximum packet size for the replication SQL and I/O threads, so that large updates using row-based replication do not cause replication to fail because an update exceeded max_allowed_packet. Setting this variable takes effect for all replication channels immediately, including running channels.

This global variable always has a value that is a positive integer multiple of 1024; if you set it to some value that is not, the value is rounded down to the next highest multiple of 1024 for it is stored or used; setting slave_max_allowed_packet to 0 causes 1024 to be used. (A truncation warning is issued in all such cases.) The default and maximum value is 1073741824 (1 GB); the minimum is 1024.

slave_net_timeout

The number of seconds to wait for more data or a heartbeat signal from the source before the replica considers the connection broken, aborts the read, and tries to reconnect. Setting this variable has no immediate effect. The state of the variable applies on all subsequent START SLAVE commands.

The first retry occurs immediately after the timeout. The interval between retries is controlled by the MASTER_CONNECT_RETRY option for the CHANGE MASTER TO statement, and the number of reconnection attempts is limited by the MASTER_RETRY_COUNT option for the CHANGE MASTER TO statement.

The heartbeat interval, which stops the connection timeout occurring in the absence of data if the connection is still good, is controlled by the MASTER_HEARTBEAT_PERIOD option for the CHANGE MASTER TO statement. The heartbeat interval defaults to half the value of slave_net_timeout, and it is recorded in the replica's connection metadata repository and shown in the replication_connection_configuration Performance Schema table. Note that a change to the value or default setting of slave_net_timeout does not automatically change the heartbeat interval, whether that has been set explicitly or is using a previously calculated default. If the connection timeout is changed, you must also issue CHANGE MASTER TO to adjust the heartbeat interval to an appropriate value so that it occurs before the connection timeout.

slave_parallel_type

When using a multithreaded replica (slave_parallel_workers is greater than 0), this variable specifies the policy used to decide which transactions are allowed to execute in parallel on the replica. The variable has no effect on replicas for which multithreading is not enabled. The possible values are:

When slave_preserve_commit_order=1 is set, you can only use LOGICAL_CLOCK.

If your replication topology uses multiple levels of replicas, LOGICAL_CLOCK may achieve less parallelization for each level the replica is away from the source. You can reduce this effect by using binlog_transaction_dependency_tracking on the source to specify that write sets are used instead of timestamps for parallelization where possible.

slave_parallel_workers

Sets the number of applier threads for executing replication transactions in parallel. Setting this variable to a number greater than 0 creates a multithreaded replica with this number of applier threads. When set to 0 (the default) parallel execution is disabled and the replica uses a single applier thread. Setting slave_parallel_workers has no immediate effect. The state of the variable applies on all subsequent START SLAVE statements.

A multithreaded replica provides parallel execution by using a coordinator thread and the number of applier threads configured by this variable. The way which transactions are distributed among applier threads is configured by slave_parallel_type. The transactions that the replica applies in parallel may commit out of order, unless slave_preserve_commit_order=1. Therefore, checking for the most recently executed transaction does not guarantee that all previous transactions from the source have been executed on the replica. This has implications for logging and recovery when using a multithreaded replica. For example, on a multithreaded replica the START SLAVE UNTIL statement only supports using SQL_AFTER_MTS_GAPS.

In MySQL 5.7, retrying of transactions is supported when multithreading is enabled on a replica. In previous versions, slave_transaction_retries was treated as equal to 0 when using multithreaded replicas.

slave_pending_jobs_size_max

For multithreaded replicas, this variable sets the maximum amount of memory (in bytes) available to worker queues holding events not yet applied. Setting this variable has no effect on replicas for which multithreading is not enabled. Setting this variable has no immediate effect. The state of the variable applies on all subsequent START SLAVE commands.

The minimum possible value for this variable is 1024; the default is 16MB. The maximum possible value is 18446744073709551615 (16 exabytes). Values that are not exact multiples of 1024 are rounded down to the next-highest multiple of 1024 prior to being stored.

The value of this variable is a soft limit and can be set to match the normal workload. If an unusually large event exceeds this size, the transaction is held until all the worker threads have empty queues, and then processed. All subsequent transactions are held until the large transaction has been completed.

slave_preserve_commit_order

For multithreaded replicas, the setting 1 for this variable ensures that transactions are externalized on the replica in the same order as they appear in the replica's relay log, and prevents gaps in the sequence of transactions that have been executed from the relay log. This variable has no effect on replicas for which multithreading is not enabled. Note that slave_preserve_commit_order=1 does not preserve the order of non-transactional DML updates, so these might commit before transactions that precede them in the relay log, which might result in gaps.

slave_preserve_commit_order=1 requires that --log-bin and --log-slave-updates are enabled on the replica, and slave_parallel_type is set to LOGICAL_CLOCK. Before changing this variable, all replication threads (for all replication channels if you are using multiple replication channels) must be stopped.

With slave_preserve_commit_order enabled, the executing thread waits until all previous transactions are committed before committing. While the thread is waiting for other workers to commit their transactions it reports its status as Waiting for preceding transaction to commit. (Prior to MySQL 5.7.8, this was shown as Waiting for its turn to commit.) Enabling this mode on a multithreaded replica ensures that it never enters a state that the source was not in. This supports the use of replication for read scale-out. See Section 16.3.4, “Using Replication for Scale-Out”.

If slave_preserve_commit_order=0 is set, the transactions that the replica applies in parallel may commit out of order. Therefore, checking for the most recently executed transaction does not guarantee that all previous transactions from the source have been executed on the replica. There is a chance of gaps in the sequence of transactions that have been executed from the replica's relay log. This has implications for logging and recovery when using a multithreaded replica. Note that the setting slave_preserve_commit_order=1 prevents gaps, but does not prevent source binary log position lag (where Exec_master_log_pos is behind the position up to which transactions have been executed). See Section 16.4.1.32, “Replication and Transaction Inconsistencies” for more information.

slave_rows_search_algorithms

When preparing batches of rows for row-based logging and replication, this variable controls how the rows are searched for matches, in particular whether hash scans are used. Setting this variable takes effect for all replication channels immediately, including running channels.

Specify a comma-separated list of the following combinations of 2 values from the list INDEX_SCAN, TABLE_SCAN, HASH_SCAN. The value is expected as a string, so if set at runtime rather than at server startup, the value must be quoted. In addition, the value must not contain any spaces. The recommended combinations (lists) and their effects are shown in the following table:

The order in which the algorithms are specified in the list makes no difference to the order in which they are displayed by a SELECT or SHOW VARIABLES statement.

It is possible to specify a single value, but this is not optimal, because setting a single value limits searches to using only that algorithm. In particular, setting INDEX_SCAN alone is not recommended, as in that case searches are unable to find rows at all if no index is present.

slave_skip_errors

Normally, replication stops when an error occurs on the replica, which gives you the opportunity to resolve the inconsistency in the data manually. This variable causes the replication SQL thread to continue replication when a statement returns any of the errors listed in the variable value.

slave_sql_verify_checksum

Cause the replication SQL thread to verify data using the checksums read from the relay log. In the event of a mismatch, the replica stops with an error. Setting this variable takes effect for all replication channels immediately, including running channels.

slave_transaction_retries

If a replication SQL thread fails to execute a transaction because of an InnoDB deadlock or because the transaction's execution time exceeded InnoDB's innodb_lock_wait_timeout or NDB's TransactionDeadlockDetectionTimeout or TransactionInactiveTimeout, it automatically retries slave_transaction_retries times before stopping with an error. Transactions with a non-temporary error are not retried.

The default value for slave_transaction_retries is 10. Setting the variable to 0 disables automatic retrying of transactions. Setting the variable takes effect for all replication channels immediately, including running channels.

As of MySQL 5.7.5, retrying of transactions is supported when multithreading is enabled on a replica. In previous versions, slave_transaction_retries was treated as equal to 0 when using multithreaded replicas.

The Performance Schema table replication_applier_status shows the number of retries that took place on each replication channel, in the COUNT_TRANSACTIONS_RETRIES column.

slave_type_conversions

Controls the type conversion mode in effect on the replica when using row-based replication. In MySQL 5.7.2 and higher, its value is a comma-delimited set of zero or more elements from the list: ALL_LOSSY, ALL_NON_LOSSY, ALL_SIGNED, ALL_UNSIGNED. Set this variable to an empty string to disallow type conversions between the source and the replica. Setting this variable takes effect for all replication channels immediately, including running channels.

ALL_SIGNED and ALL_UNSIGNED were added in MySQL 5.7.2 (Bug#15831300). For additional information on type conversion modes applicable to attribute promotion and demotion in row-based replication, see Row-based replication: attribute promotion and demotion.

sql_slave_skip_counter

The number of events from the source that a replica should skip. Setting the option has no immediate effect. The variable applies to the next START SLAVE statement; the next START SLAVE statement also changes the value back to 0. When this variable is set to a nonzero value and there are multiple replication channels configured, the START SLAVE statement can only be used with the FOR CHANNEL channel clause.

This option is incompatible with GTID-based replication, and must not be set to a nonzero value when gtid_mode=ON. If you need to skip transactions when employing GTIDs, use gtid_executed from the source instead. See Section 16.1.7.3, “Skipping Transactions”.

sync_master_info

The effects of this variable on a replica depend on whether the replica's master_info_repository is set to FILE or TABLE, as explained in the following paragraphs.

master_info_repository = FILE.  If the value of sync_master_info is greater than 0, the replica synchronizes its master.info file to disk (using fdatasync()) after every sync_master_info events. If it is 0, the MySQL server performs no synchronization of the master.info file to disk; instead, the server relies on the operating system to flush its contents periodically as with any other file.

master_info_repository = TABLE.  If the value of sync_master_info is greater than 0, the replica updates its connection metadata repository table after every sync_master_info events. If it is 0, the table is never updated.

The default value for sync_master_info is 10000. Setting this variable takes effect for all replication channels immediately, including running channels.

sync_relay_log

If the value of this variable is greater than 0, the MySQL server synchronizes its relay log to disk (using fdatasync()) after every sync_relay_log events are written to the relay log. Setting this variable takes effect for all replication channels immediately, including running channels.

Setting sync_relay_log to 0 causes no synchronization to be done to disk; in this case, the server relies on the operating system to flush the relay log's contents from time to time as for any other file.

A value of 1 is the safest choice because in the event of an unexpected halt you lose at most one event from the relay log. However, it is also the slowest choice (unless the disk has a battery-backed cache, which makes synchronization very fast). For information on the combination of settings on a replica that is most resilient to unexpected halts, see Section 16.3.2, “Handling an Unexpected Halt of a Replica”.

sync_relay_log_info

The default value for sync_relay_log_info is 10000. Setting this variable takes effect for all replication channels immediately, including running channels.

The effects of this variable on the replica depend on the server's relay_log_info_repository setting (FILE or TABLE). If the setting is TABLE, the effects of the variable also depend on whether the storage engine used by the relay log info table is transactional (such as InnoDB) or not transactional (MyISAM). The effects of these factors on the behavior of the server for sync_relay_log_info values of zero and greater than zero are as follows: