MySQL 5.1 Reference Manual  /  ...  /  Advantages and Disadvantages of Statement-Based and Row-Based Replication Advantages and Disadvantages of Statement-Based and Row-Based Replication

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
  • Proven technology that has existed in MySQL since 3.23.

  • 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 INSERT DELETE, UPDATE, and REPLACE statements) can be replicated using statement-based replication. Any nondeterministic behavior is difficult to replicate when using statement-based replication. Examples of such DML (Data Modification Language) statements include the following:

    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 SHOW WARNINGS.

  • INSERT ... SELECT requires a greater number of row-level locks than with row-based replication.

  • UPDATE statements that require a table scan (because no index is used in the WHERE clause) must lock a greater number of rows than with row-based replication.

  • For InnoDB: An INSERT statement that uses AUTO_INCREMENT blocks other nonconflicting INSERT statements.

  • For complex statements, the statement must be evaluated and executed on the slave before the rows are updated or inserted. With row-based replication, the slave only has to modify the affected rows, not execute the full statement.

  • If there is an error in evaluation on the slave, particularly when executing complex statements, statement-based replication may slowly increase the margin of error across the affected rows over time. See Section, “Slave Errors During Replication”.

  • Stored functions execute with the same NOW() value as the calling statement. However, this is not true of stored procedures.

  • Deterministic UDFs must be applied on the slaves.

  • Table definitions must be (nearly) identical on master and slave. See Section, “Replication with Differing Table Definitions on Master and Slave”, for more information.

Advantages of Row-Based Replication
  • All changes can be replicated. This is the safest form of replication.

    For MySQL versions earlier than 5.1.14, DDL (Data Definition Language) statements such as CREATE TABLE are replicated using statement-based replication, while DML statements, as well as GRANT and REVOKE statements, are replicated using row-based replication.

    In MySQL 5.1.14 and later, the mysql database is not replicated. The mysql database is instead seen as a node-specific database. Row-based replication is not supported on tables in this database. Instead, statements that would normally update this information—such as GRANT, REVOKE and the manipulation of triggers, stored routines (including stored procedures), and views—are all replicated to slaves using statement-based replication.

    For statements such as CREATE TABLE ... SELECT, a CREATE statement is generated from the table definition and replicated using statement-based format, while the row insertions are replicated using row-based format.

  • The technology is the same as in most other database management systems; knowledge about other systems transfers to MySQL.

  • Fewer row locks are required on the master, which thus achieves higher concurrency, for the following types of statements:

  • Fewer row locks are required on the slave for any INSERT, UPDATE, or DELETE statement.

Disadvantages of Row-Based Replication
  • RBR tends to generate more data that must be logged. To replicate a DML statement (such as an UPDATE or DELETE statement), 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 taking and restoring from 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.

  • Deterministic UDFs that generate large BLOB values take longer to replicate with row-based replication than with statement-based replication. This is because the BLOB column value is logged, rather than the statement generating the data.

  • You cannot examine the logs to see what statements were executed, nor can you see on the slave what statements were received from the master and executed.

    However, beginning with MySQL 5.1.29, you can see what data was changed using mysqlbinlog with the options --base64-output=DECODE-ROWS and --verbose.

  • For tables using the MyISAM storage engine, a stronger lock is required on the slave for INSERT statements when applying them as row-based events to the binary log than when applying them as statements. This means that concurrent inserts on MyISAM tables are not supported when using row-based replication.

  • Formerly, when performing a bulk operation that includes nontransactional storage engines, changes were applied as the statement executed. With row-based logging, this meant that the binary log was written while the statement was running. On the master, this does not cause problems with concurrency, because tables are locked until the bulk operation terminates. On the slave server, tables were not locked while the slave applied changes, because the slave did not know that those changes were part of a bulk operation.

    In such cases, if you retrieved data from a table on the master (for example, using SELECT * FROM table_name), the server waited for the bulk operation to complete before executing the SELECT statement, because the table was read-locked. On the slave, the server did not wait (because there was no lock). This meant that, until the bulk operation on the slave completed, different results were obtained for the same SELECT query on the master and on the slave.

    This issue was resolved in MySQL 5.1.24. (Bug #29020)

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User Comments
  Posted by Ben Clewett on March 7, 2012
Memory tables have caused me a problem with ROW based replication.

As the table is not populated on server start-up, my slave may have an empty table, where the master is populated.

When I 'START SLAVE' I get:

Could not execute Update_rows event on table; Can't find record in 'foo', Error_code: 1032; handler error HA_ERR_KEY_NOT_FOUND; the event's master log mysql_bin_log.000022, end_log_pos 576268563

This is not the case with STATEMENT based replication, which will work.

In my case I solved this by using 'replicate_ignore_table' for any memory tables.

(Although a more elegant solution to keep this table functional would be preferable, if known?)

  Posted by Peter Burns on March 28, 2014
Another disadvantage of row-based replication:

If you have 2 or more servers replicating in a loop then some statements which are safe for SBR can cause RBR to fail, in particular statements which increment or decrement values. E.g.

UPDATE counter_table SET counter = counter + 1;

In SBR, 2 servers can both execute this query many times and ultimately stay in sync (even if replication halts for a while). But in RBR, if both servers execute this query at about the same time (or while replication is halted) they can both log the same change (e.g. from counter = 55 to counter = 56), and this change will fail when it replicates to the other server.

  Posted by Ben Lin on April 15, 2014
@Peter: Sounds like you are using both "servers" as masters, and replicate from each other. That is not a very good (common) practice. Usually there is only one master, and all the write operations are performed in this master. The other servers are slave for reading.
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