… does transaction isolation affects purging ? Innodb is smart and trying to purge data as soon as possible. In default (REPEATABLE-READ) mode Innodb has to maintain versions back to the first data read the oldest transaction has performed because it is possible for that transaction to require state of any row in Innodb table at that point in time. If you use READ-COMMITTED mode Innodb does…
Post: Ultimate MySQL variable and status reference list
January 8, 2011 By 4 Comments
…transaction_alloc_block_sizeblogpercona.commanual transaction_isolationblogpercona.commanual transaction…
Post: INSERT INTO ... SELECT Performance with Innodb tables.
July 12, 2006 By 22 Comments
… slave. If Innodb would not locking rows in source table other transaction could modify the row and commit before transaction which is running… one of INSERT … SELECT you may execute this transaction in READ-COMMITTED isolation mode. Other workarounds are less general purpose. For example…
Post: Innodb Table Locks
July 31, 2012 By 4 Comments
… select but add LOCK IN SHARE MODE so it performs locking reads to validate our theory: —TRANSACTION 12305, ACTIVE 9 sec mysql… “IS” mode and there are number of row level locks in “S” mode. What does it mean ? Well we asked Innodb to do…. You almost never will run into problems with Innodb table level locks because innodb will only set intentional level locks for everything…
Post: InnoDB's gap locks
March 27, 2012 By 15 Comments
…? Is possible to detect those gap locks using SHOW ENGINE INNODB STATUS: —TRANSACTION 72C, ACTIVE 755 sec 4 lock struct(s), heap…_CLUST_INDEX` of table `test`.`t` trx id 72C lock_mode X locks rec but not gap RECORD LOCKS space id… change during a transaction, so there is no need to create locks to prevent that from happening. 2- innodb_locks_unsafe_for…
Post: When does Innodb Start Transaction ?
January 11, 2011 By 9 Comments
… – setting this mode will NOT start transaction however reading or writing Innodb table will. I would call it delayed transaction creation – having transaction open is costly, especially in repeatable-read mode…
Post: SELECT LOCK IN SHARE MODE and FOR UPDATE
August 6, 2006 By 51 Comments
… SHARE MODE modifiers effectively run in READ-COMMITTED isolation mode even if current isolation mode is REPEATABLE-READ. This is done beause Innodb can… scheduling At this point transaction which made least updates is killed to resolve deadlock. Which means if transaction takes a lot of…
Post: How much memory Innodb locks really take ?
July 13, 2006 By 11 Comments
…, query id 24542 localhost root show innodb status Note, running statement in consistent read mode which does not set any locks is… “5%” lock in share mode; +———-+ | count(*) | +———-+ | 102216 | +———-+ 1 row in set (4.44 sec) Looking at SHOW INNODB STATUS we can see: Total number of lock structs in row lock hash table 440 LIST OF TRANSACTIONS FOR EACH SESSION: —TRANSACTION…
Post: MVCC: Transaction IDs, Log Sequence numbers and Snapshots
December 19, 2007 By 3 Comments
… bit. This is general explanation, it does not corresponds to Innodb in particular and some implementation can be different but I… consider transaction 101 which is running in REPEATABLE-READ isolation mode and which was started before transaction 100 have committed. In such case transaction 101 should not see changes done by transaction 100…
Post: The perils of InnoDB with Debian and startup scripts
January 28, 2009 By 13 Comments
… 139 a writer (thread id 1158064464) has reserved it in mode exclusive number of readers 0, waiters flag 1 Last time… 1158064464 which has reserved it. If you hunt through the TRANSACTIONS section, you can see the OS thread IDs, and that… threads: —TRANSACTION 0 228527423, ACTIVE 0 sec, process no 30034, OS thread id 1159956816 starting index read, thread declared inside InnoDB 500…
