Each binary logging format has advantages and disadvantages. For most users, the mixed replication format should provide the best combination of data integrity and performance. If, however, you want to take advantage of the features specific to the statement-based or row-based replication format when performing certain tasks, you can use the information in this section, which provides a summary of their relative advantages and disadvantages, to determine which is best for your needs.
Advantages of statement-based replication
Less data written to log files. When updates or deletes affect many rows, this results in much less storage space required for log files. This also means that taking and restoring from backups can be accomplished more quickly.
Log files contain all statements that made any changes, so they can be used to audit the database.
Disadvantages of statement-based replication
Statements that are unsafe for SBR. Not all statements which modify data (such as
REPLACEstatements) can be replicated using statement-based replication. Any nondeterministic behavior is difficult to replicate when using statement-based replication. Examples of such Data Modification Language (DML) statements include the following:
A statement that depends on a loadable function or stored program that is nondeterministic, since the value returned by such a function or stored program or depends on factors other than the parameters supplied to it. (Row-based replication, however, simply replicates the value returned by the function or stored program, so its effect on table rows and data is the same on both the source and replica.) See Section 18.104.22.168, “Replication of Invoked Features”, for more information.
UPDATEstatements that use a
LIMITclause without an
ORDER BYare nondeterministic. See Section 22.214.171.124, “Replication and LIMIT”.
Locking read statements (
SELECT ... FOR UPDATEand
SELECT ... FOR SHARE) that use
SKIP LOCKEDoptions. See Locking Read Concurrency with NOWAIT and SKIP LOCKED.
Deterministic loadable functions must be applied on the replicas.
Statements using any of the following functions cannot be replicated properly using statement-based replication:
SYSDATE()(unless both the source and the replica are started with the
However, all other functions are replicated correctly using statement-based replication, including
NOW()and so forth.
For more information, see Section 126.96.36.199, “Replication and System Functions”.
Statements that cannot be replicated correctly using statement-based replication are logged with a warning like the one shown here:
[Warning] Statement is not safe to log in statement format.
A similar warning is also issued to the client in such cases. The client can display it using
INSERT ... SELECTrequires a greater number of row-level locks than with row-based replication.
UPDATEstatements that require a table scan (because no index is used in the
WHEREclause) must lock a greater number of rows than with row-based replication.
INSERTstatement that uses
AUTO_INCREMENTblocks other nonconflicting
For complex statements, the statement must be evaluated and executed on the replica before the rows are updated or inserted. With row-based replication, the replica only has to modify the affected rows, not execute the full statement.
If there is an error in evaluation on the replica, particularly when executing complex statements, statement-based replication may slowly increase the margin of error across the affected rows over time. See Section 188.8.131.52, “Replica Errors During Replication”.
Stored functions execute with the same
NOW()value as the calling statement. However, this is not true of stored procedures.
Deterministic loadable functions must be applied on the replicas.
Table definitions must be (nearly) identical on source and replica. See Section 184.108.40.206, “Replication with Differing Table Definitions on Source and Replica”, for more information.
As of MySQL 8.0.22, DML operations that read data from MySQL grant tables (through a join list or subquery) but do not modify them are performed as non-locking reads on the MySQL grant tables and are therefore not safe for statement-based replication. For more information, see Grant Table Concurrency.
Advantages of row-based replication
All changes can be replicated. This is the safest form of replication.Note
Statements that update the information in the
mysqlsystem schema, such as
REVOKEand the manipulation of triggers, stored routines (including stored procedures), and views, are all replicated to replicas using statement-based replication.
For statements such as
CREATE TABLE ... SELECT, a
CREATEstatement is generated from the table definition and replicated using statement-based format, while the row insertions are replicated using row-based format.
Fewer row locks are required on the source, which thus achieves higher concurrency, for the following types of statements:
WHEREclauses that do not use keys or do not change most of the examined rows.
Fewer row locks are required on the replica for any
Disadvantages of row-based replication
RBR can generate more data that must be logged. To replicate a DML statement (such as an
DELETEstatement), statement-based replication writes only the statement to the binary log. By contrast, row-based replication writes each changed row to the binary log. If the statement changes many rows, row-based replication may write significantly more data to the binary log; this is true even for statements that are rolled back. This also means that making and restoring a backup can require more time. In addition, the binary log is locked for a longer time to write the data, which may cause concurrency problems. Use
binlog_row_image=minimalto reduce the disadvantage considerably.
Deterministic loadable functions that generate large
BLOBvalues take longer to replicate with row-based replication than with statement-based replication. This is because the
BLOBcolumn value is logged, rather than the statement generating the data.
You cannot see on the replica what statements were received from the source and executed. However, you can see what data was changed using mysqlbinlog with the options
Alternatively, use the
binlog_rows_query_log_eventsvariable, which if enabled adds a
Rows_queryevent with the statement to mysqlbinlog output when the
-vvoption is used.
For tables using the
MyISAMstorage engine, a stronger lock is required on the replica for
INSERTstatements when applying them as row-based events to the binary log than when applying them as statements. This means that concurrent inserts on
MyISAMtables are not supported when using row-based replication.