Binlogging and replication improvements

Due to continuous development, Percona Server for MySQL incorporated a number of improvements related to replication and binary logs handling. This resulted in replication specifics, which distinguishes it from MySQL.

Safety of statements with a LIMIT clause

Summary of the Fix

MySQL considers all UPDATE/DELETE/INSERT ... SELECT statements with LIMIT clause to be unsafe, no matter wether they are really producing non-deterministic result or not, and switches from statement-based logging to row-based one. Percona Server for MySQL is more accurate, it acknowledges such instructions as safe when they include ORDER BY PK or WHERE condition. This fix has been ported from the upstream bug report #42415 (#44).

Performance improvement on relay log position update

Summary of the Fix

MySQL always updated relay log position in multi-source replications setups regardless of whether the committed transaction has already been executed or not. Percona Server omits relay log position updates for the already logged GTIDs.

Details

Particularly, such unconditional relay log position updates caused additional fsync operations in case of relay-log-info-repository=TABLE, and with the higher number of channels transmitting such duplicate (already executed) transactions the situation became proportionally worse. Bug fixed #1786 (upstream #85141).

Performance improvement on source and connection status updates

Summary of the Fix

Replica nodes configured to update source status and connection information only on log file rotation did not experience the expected reduction in load. MySQL was additionally updating this information in case of multi-source replication when replica had to skip the already executed GTID event.

Details

The configuration with master_info_repository=TABLE and sync_master_info=0 makes replica to update source status and connection information in this table on log file rotation and not after each sync_master_info event, but it didn’t work on multi-source replication setups. Heartbeats sent to the replica to skip GTID events which it had already executed previously, were evaluated as relay log rotation events and reacted with mysql.slave_master_info table sync. This inaccuracy could produce huge (up to 5 times on some setups) increase in write load on the replica, before this problem was fixed in Percona Server for MySQL. Bug fixed #1812 (upstream #85158).

Writing FLUSH Commands to the Binary Log

FLUSH commands, such as FLUSH SLOW LOGS, are not written to the binary log if the system variable binlog_skip_flush_commands is set to ON.

In addition, the following changes were implemented in the behavior of read_only and super_read_only modes:

  • When read_only is set to ON, any FLUSH ... command executed by a normal user (without the SUPER privilege) are not written to the binary log regardless of the value of the binlog_skip_flush_command variable.
  • When super_read_only is set to ON, any FLUSH ... command executed by any user (even by those with the SUPER privilege) are not written to the binary log regardless of the value of the binlog_skip_flush_command variable.

An attempt to run a FLUSH command without either SUPER or RELOAD privileges results in the ER_SPECIFIC_ACCESS_DENIED_ERROR exception regardless of the value of the binlog_skip_flush_command variable.

variable binlog_skip_flush_commands
Version Info:
Command Line:

Yes

Config File:

Yes

Scope:

Global

Dynamic:

Yes

Default Value:

OFF

When binlog_skip_flush_command is set to ON, FLUSH ... commands are not written to the binary log. See Writing FLUSH Commands to the Binary Log for more information about what else affects the writing of FLUSH commands to the binary log.

Note

FLUSH LOGS, FLUSH BINARY LOGS, FLUSH TABLES WITH READ LOCK, and FLUSH TABLES ... FOR EXPORT are not written to the binary log no matter what value the binlog_skip_flush_command variable contains. The FLUSH command is not recorded to the binary log and the value of binlog_skip_flush_command is ignored if the FLUSH command is run with the NO_WRITE_TO_BINLOG keyword (or its alias LOCAL).

See also

MySQL Documentation: FLUSH Syntax
https://dev.mysql.com/doc/refman/8.0/en/flush.html

Binary Log User Defined Functions

To implement Point in Time recovery, we have added the binlog_utils_udf. The following user-defined functions are included:

Name Returns Description
get_binlog_by_gtid() Binlog file name as STRING Returns the binlog file name that contains the specified GTID
get_last_gtid_from_binlog() GTID as STRING Returns the last GTID found in the specified binlog
get_gtid_set_by_binlog() GTID set as STRING Returns all GTIDs found in the specified binlog
get_binlog_by_gtid_set() Binlog file name as STRING Returns the file name of the binlog which contains at least one GTID from the specified set.
get_first_record_timestamp_by_binlog() Timestamp as INTEGER Returns the timestamp of the first event in the specified binlog
get_last_record_timestamp_by_binlog() Timestamp as INTEGER Returns the timestamp of the last event in the specified binlog

Note

All functions returning timestamps return their values as microsecond precision UNIX time. In other words, they represent the number of microseconds since 1-JAN-1970.

All functions accepting a binlog name as the parameter accepts only short names, without a path component. If the path separator (‘/’) is found in the input, an error is returned. This serves the purpose of restricting the locations from where binlogs can be read. They are always read from the current binlog directory (@@log_bin_basename system variable).

All functions returning binlog file names return the name in short form, without a path component.

The basic syntax for get_binlog_by_gtid() is the following:

  • get_binlog_by_gtid(string) [AS] alias

    Usage: SELECT get_binlog_by_gtid(string) [AS] alias

    Example:

    CREATE FUNCTION get_binlog_by_gtid RETURNS STRING SONAME 'binlog_utils_udf.so';
    SELECT get_binlog_by_gtid("F6F54186-8495-47B3-8D9F-011DDB1B65B3:1") AS result;
    +--------------+
    | result       |
    +==============+
    | binlog.00001 |
    +--------------+
    
    DROP FUNCTION get_binlog_by_gtid;
    

The basic syntax for get_last_gtid_from_binlog() is the following:

  • get_last_gtid_from_binlog(string) [AS] alias

    Usage: SELECT get_last_gtid_from_binlog(string) [AS] alias

    Example:

    CREATE FUNCTION get_last_gtid_from_binlog RETURNS STRING SONAME 'binlog_utils_udf.so';
    SELECT get_last_gtid_from_binlog("binlog.00001") AS result;
    +-----------------------------------------+
    | result                                  |
    +=========================================+
    | F6F54186-8495-47B3-8D9F-011DDB1B65B3:10 |
    +-----------------------------------------+
    
    DROP FUNCTION get_last_gtid_from_binlog;
    

The basic syntax for get_gtid_set_by_binlog() is the following:

  • get_gtid_set_by_binlog(string) [AS] alias

    Usage: SELECT get_gtid_set_by_binlog(string) [AS] alias

    Example:

    CREATE FUNCTION get_gtid_set_by_binlog RETURNS STRING SONAME 'binlog_utils_udf.so';
    SELECT get_gtid_set_by_binlog("binlog.00001") AS result;
    +-------------------------+
    | result                  |
    +=========================+
    | 11ea-b9a7:7,11ea-b9a7:8 |
    +-------------------------+
    
    DROP FUNCTION get_gtid_set_by_binlog;
    

The basic syntax for get_binlog_by_gtid_set() is the following:

  • get_binlog_by_gtid_set(string) [AS] alias

    Usage: SELECT get_binlog_by_gtid_set(string) [AS] alias

    Example:

    CREATE FUNCTION get_binlog_by_gtid_set RETURNS STRING SONAME 'binlog_utils_udf.so';
    SELECT get_binlog_by_gtid_set("11ea-b9a7:7,11ea-b9a7:8") AS result;
    +---------------------------------------------------------------+
    | result                                                        |
    +===============================================================+
    | bin.000003                                                    |
    +---------------------------------------------------------------+
    
    DROP FUNCTION get_binlog_by_gtid_set;
    

The basic syntax for get_first_record_timestamp_by_binlog() is the following:

  • get_first_record_timestamp_by_binlog(TIMESTAMP) [AS] alias

    Usage: SELECT get_first_record_timestamp_by_binlog(TIMESTAMP) [AS] alias

    Example:

    CREATE FUNCTION get_first_record_timestamp_by_binlog RETURNS STRING SONAME 'binlog_utils_udf.so';
    SELECT FROM_UNIXTIME(get_first_record_timestamp_by_binlog("bin.00003") DIV 1000000) AS result;
    +---------------------+
    | result              |
    +=====================+
    | 2020-12-03 09:10:40 |
    +---------------------+
    
    DROP FUNCTION get_first_record_timestamp_by_binlog;
    

The basic syntax for get_last_record_timestamp_by_binlog() is the following:

  • get_last_record_timestamp_by_binlog(TIMESTAMP) [AS] alias

    Usage: SELECT get_last_record_timestamp_by_binlog(TIMESTAMP) [AS] alias

    Example:

    CREATE FUNCTION get_last_record_timestamp_by_binlog RETURNS STRING SONAME 'binlog_utils_udf.so';
    SELECT FROM_UNIXTIME(get_last_record_timestamp_by_binlog("bin.00003") DIV 1000000) AS result;
    +---------------------+
    | result              |
    +=====================+
    | 2020-12-04 04:18:56 |
    +---------------------+
    
    DROP FUNCTION get_last_record_timestamp_by_binlog;
    

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