… locks all index records found by the WHERE clause with an exclusive lock and the gaps between them with a shared gap lock. This lock… `test`.`t` trx id 72C lock_mode X locks gap before rec If you have lot of gaps locks in your transactions affecting the concurrency and the performance you can disable them in two different ways: 1…
Post: SELECT LOCK IN SHARE MODE and FOR UPDATE
August 6, 2006 By 51 Comments
… and LOCK IN SHARE MODE sees it. What is happening ? SELECT for UPDATE and LOCK IN SHARE MODE modifiers effectively run in READ-COMMITTED isolation mode even if current isolation mode… it also works if LOCK IN SHARE MODE is used with selects – standard selects are run in non-locking mode which means they never lock any rows and…
Post: How much memory Innodb locks really take ?
July 13, 2006 By 11 Comments
… sec) mysql> select count(i) from sample lock in share mode; +———-+ | count(i) | +———-+ | 1638400 | +———-+ 1 row in set (7.02 sec) Looking at SHOW INNODB…%” 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…
Post: INSERT INTO ... SELECT Performance with Innodb tables.
July 12, 2006 By 21 Comments
… perform non locking reads, meaning unless you use some modifiers such as LOCK IN SHARE MODE or FOR UPDATE, SELECT statements will not lock any rows… in READ-COMMITTED mode, potentially giving different result compared to what pure SELECT would give. This by the way applies to SELECT .. LOCK IN SHARE MODE…
Post: Test Drive of Solid
September 22, 2006 By 5 Comments
… if rows are locked or even modified unless you require locking read, in which case SELECT FOR UPDATE or SELECT … LOCK IN SHARE MODE can be used… will do READ-COMMITED for locking reads (SELECT FOR UPDATE/LOCK IN SHARE MODE) as only actual row versions can be locked. With Innodb we would…
Post: Paul McCullagh answers your questions about PBXT
November 20, 2009 By 2 Comments
… InnoDB in REPEATABLE READ mode. On the other hand, there are currently no plans to implement InnoDB style “gap locking“. Gap locking effectively involves locking… rows are selected in this manner. I should also mention that the consequence of this is that SELECT … LOCK IN SHARE MODE is currently not… startup it is holding the global LOCK_plugin lock. In init, the engine needs to do recovery. In PBXT’s case this means opening…
Comment: SELECT LOCK IN SHARE MODE and FOR UPDATE
January 27, 2010 By 51 Comments
… no ULOCK in innodb…:(… okay..i’ll just read more about lock compatibility…so it means to say ill be using shared/exclusive… put the lock on the query for example this one SELECT pep_id, pep_name FROM person WHERE id= $id LOCK IN SHARE MODE; OR ill just do it like this function InsertData { $query = “LOCK TABLE person IN SHARE MODE“; $query = INSERT INTO person…
Post: Table locks in SHOW INNODB STATUS
June 8, 2010 By 1 Comment
…locking and use table locks instead. I’ve seen various theories ranging from lock escalation to using table locks in…locks – Intention exclusive lock does not prevent other threads taking intention shared or even intention exclusive locks…
Comment: SELECT LOCK IN SHARE MODE and FOR UPDATE
October 20, 2007 By 51 Comments
… USERS WHERE NAME LIKE “%Heikki%” LOCK IN SHARE MODE TR1 – END If the DELETE statement of TR1 would not lock all records, then the INSERT… USERS table). In my example the SELECT of TR2 uses a SHARE LOCK (I agree that this is a question of locking). Now the DELETE of TR1 does not ‘see’ record “HeikkiTuuri”, whereas the SELECT of TR1 does. This is in contraction…
Comment: INSERT INTO ... SELECT Performance with Innodb tables.
January 1, 2012 By 21 Comments
…josh: No this does not applies in MySQL 5.5+. I’ve already check that on a … mln rows using insert into select from this table. No lock has been aquired and on the other thread i could… have this exact behaviour you can use mentioned above: “lock in share mode” because this does the lock to be aqquired on the second table
