Documentation Home
MySQL Internals Manual
Download this Manual
EPUB - 1.2Mb


MySQL Internals Manual  /  ...  /  Determining the Logging Format

19.4.1 Determining the Logging Format

For each statement, we must determine the logging format: row or statement. This is done as follows.

  1. At parse time, it is detected if the statement is unsafe to log in statement format (that is, requires row format). If this is the case, the THD::Lex::set_stmt_unsafe() function is called. This must be done prior to the call to THD::decide_logging_format() (that is, prior to lock_tables). As a special case, some types of unsafeness are detected inside THD::decide_logging_format(), before the logging format is decided. Note that statements shall be marked unsafe even if binlog_format!=mixed.

  2. THD::decide_logging_format() determines the logging format, based on the value of binlog_format and the unsafeness of the current statement.

  3. THD::decide_logging_format() also determines if the statement is impossible to log, in which case it generates an error and the statement is not executed. The statement may be impossible to log for the following reasons:

    • both row-incapable engines and statement-incapable engines are involved (ER_BINLOG_ROW_ENGINE_AND_STMT_ENGINE)

    • BINLOG_FORMAT = ROW and at least one table uses a storage engine limited to statement-logging (ER_BINLOG_ROW_MODE_AND_STMT_ENGINE)

    • statement is unsafe, BINLOG_FORMAT = MIXED, and storage engine is limited to statement-logging and (ER_BINLOG_UNSAFE_AND_STMT_ENGINE)

    • statement is a row injection (that is, a row event executed by the slave SQL thread or a BINLOG statement) and at least one table uses a storage engine limited to statement-logging (ER_BINLOG_ROW_INJECTION_AND_STMT_ENGINE)

    • BINLOG_FORMAT = STATEMENT and at least one table uses a storage engine limited to row-logging (ER_BINLOG_STMT_MODE_AND_ROW_ENGINE)

    • statement is a row injection (that is, a row event executed by the slave SQL thread or a BINLOG statement) and BINLOG_FORMAT = STATEMENT (ER_BINLOG_ROW_INJECTION_AND_STMT_MODE)

    • more than one engine is involved and at least one engine is self-logging (ER_BINLOG_MULTIPLE_ENGINES_AND_SELF_LOGGING_ENGINE)

    See the comment above decide_logging_format for details.

  4. THD::decide_logging_format() also determines if a warning shall be issued. A warning is issued for unsafe statements if binlog_format=STATEMENT. Warnings are not issued immediately; instead, THD::binlog_stmt_unsafe_flags is set and the warning is issued in THD::binlog_query(). This prevents warnings in the case that the statement generates an error later so that it is not logged.

Sub-statements. Let T be a statement that invokes an unsafe sub-statement S (S may be a stored function, stored procedure, trigger, view, or prepared statement). Each sub-statement is cached as an sp_head object. The sp_head object stores the Lex that was generated when the statement defining the sub-statement was parsed (that is, when CREATE FUNCTION/CREATE PROCEDURE/CREATE TRIGGER/CREATE VIEW/PREPARE was parsed). Hence, this cached Lex has the unsafe flag set. When T is parsed, it fetches S from the cache. At this point, it calls sp_head::propagate_attributes(), which marks the current Lex object as unsafe if the cached Lex object was unsafe.


User Comments
Sign Up Login You must be logged in to post a comment.