… yet been committed at the current point in time, and thus should not be visible in the consistent read. For the REPEATABLE_READ isolation level, the snapshot is created on the first SELECT for each transaction. For lower isolation levels it is…
Post: trx descriptors: MySQL performance improvements in Percona Server 5.5.30-30.2
April 12, 2013 By 3 Comments
Post: Differences between READ-COMMITTED and REPEATABLE-READ transaction isolation levels
August 28, 2012 By 3 Comments
… asked about the differences between the READ COMMITTED and REPEATABLE READ transaction isolation levels. There are a few differences between READ-COMMITTED and REPEATABLE-READ, and they are all related… transaction isolation levels InnoDB creates locks over every index entry scanned. The difference between the levels is that once the statement completes in READ COMMITTED…
Post: InnoDB's gap locks
March 27, 2012 By 15 Comments
… REPEATABLE READ for read-only SELECT, but it behaves as if you use READ COMMITTED for all write queries, in spite of your chosen transaction isolation level (considering only the two most common isolation levels, REPEATABLE READ and READ COMMITTED). What…
Comment: InnoDB's gap locks
April 13, 2012 By 15 Comments
… REPEATABLE READ for read-only SELECT, but it behaves as if you use READ COMMITTED for all write queries, in spite of your chosen transaction isolation level” I have two sessions with REPEATABLE READ transaction isolation level. mysql> show…
Post: Test Drive of Solid
September 22, 2006 By 5 Comments
…reads in the repeatable read isolation level. Solid has OPTMISTIC (default) and PESSIMISTIC concurrency control, so it was interesting to test both. We used default isolation… behavior is different from Innodb which will do READ-COMMITED for locking reads (SELECT FOR UPDATE/LOCK IN SHARE MODE) as…
Post: READ-COMMITED vs REPETABLE-READ in tpcc-like load
February 11, 2010 By 6 Comments
… isolation level is poping up again and again. Recently it was discussed in InnoDB : Any real performance improvement when using READ COMMITED isolation level ? and in Repeatable read versus read committed for InnoDB . Serge in his post explains why READ COMMITED is better for TPCC…
Post: Innodb undo segment size and transaction isolation
January 12, 2011 By 3 Comments
…default (REPEATABLE-READ) mode Innodb has to maintain versions back to the first data read the …even if you set transaction isolation to lowest READ-UNCOMMITTED level Innodb will not purge the…isolation mode to READ-COMMITTED can be good idea if your application supports it. Note you can set isolation…
Post: Paul McCullagh answers your questions about PBXT
November 20, 2009 By 2 Comments
…(equivalent to innodb_flush_log_at_trx_commit=2). A major change was completed at…REPEATABLE READ mode, then there is essentially no difference in the isolation paradigm between the two engines. REPEATABLE READ…the Falcon storage engine. PBXT supports row-level locking and foreign keys. Does this …
Post: Innodb performance gotcha w Larger queries.
August 28, 2009 By 7 Comments
….0 does scanning the SQL for each time. if (trx->isolation_level select_lock_type != LOCK_NONE && trx->mysql_query_str) { /* Scan…); if (success) { /* It is a plain locking SELECT and the isolation level is low: do not lock gaps */ set_also_gap_locks…, current 5.1 at the same place is, if (trx->isolation_level select_lock_type != LOCK_NONE && trx->mysql_thd != NULL && thd…
Comment: READ-COMMITED vs REPETABLE-READ in tpcc-like load
February 12, 2010 By 6 Comments
… with read-committed isolation level as the commonly used repeatable-read. We have now changed isolation level to default(repeatable read). This has resulted in noticeable more deadlocks than read-committed, and… me it seems strange that repeatable-read gives less deadlocks compared to read-committed as it is a higher isolation level and therefore must lock more…
