… rows while SELECT for UPDATE 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 is…
Post: INSERT INTO ... SELECT Performance with Innodb tables.
July 12, 2006 By 22 Comments
… tables 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… performed 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 and SELECT…
Post: Innodb Table Locks
July 31, 2012 By 4 Comments
… same select but add LOCK IN SHARE MODE so it performs locking reads to validate our theory: —TRANSACTION 12305, ACTIVE 9 sec mysql tables in use 2, locked… root Sending data select count(*) from sbtest,sbtest x lock in share mode TABLE LOCK table `sbtest`.`sbtest` trx id 12305 lock mode IS RECORD LOCKS space id 84…
Post: Test Drive of Solid
September 22, 2006 By 5 Comments
… even 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. Quite possibly it is a bug which will be fixed in…
Post: How much memory Innodb locks really take ?
July 13, 2006 By 11 Comments
… affected (0.00 sec) mysql> select count(i) from sample lock in share mode; +———-+ | count(i) | +———-+ | 1638400 | +———-+ 1 row in set (7.02 sec) Looking at… (0.00 sec) mysql> select count(*) from sample where j like “5%” lock in share mode; +———-+ | count(*) | +———-+ | 102216 | +———-+ 1 row in set (4.44 sec) Looking…
Post: Implications of Metadata Locking Changes in MySQL 5.5
February 1, 2013 By 9 Comments
… in REPEATABLE-READ isolation mode is ACTIVE. session1 > select @@tx_isolation; +—————–+ | @@tx_isolation | +—————–+ | REPEATABLE-READ | +—————–+ 1 row in set…a multi-step process, the old table is locked in shared mode and then something similar to the following …
Post: Paul McCullagh answers your questions about PBXT
November 20, 2009 By 2 Comments
…: to support SELECT FOR UPDATE, and to avoid optimistic locking errors. This makes PBXT’s behavior identical to InnoDB in REPEATABLE READ mode. On… millions of 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…
Comment: Are PHP persistent connections evil ?
November 14, 2008 By 32 Comments
…! in PHP mySQL, the use of SELECT FOR UPDATE and SELECT LOCK IN SHARE MODE, How to use it? They don’t make any sense to me in a web application, because when you first read the data (SELECT FOR UPDATE)the script ends… is an auto mysql_close.(Which would rollback your transaction in the SELECT) With a persistent connection, may be it would keep…
Comment: SELECT LOCK IN SHARE MODE and FOR UPDATE
January 28, 2010 By 51 Comments
… explaination is: SELECT … FOR UPDATE sets a XLOCK on the accessed record. SELECT … LOCK IN SHARE MODE sets a SLOCK on the accessed record. In both cases…
Comment: SELECT LOCK IN SHARE MODE and FOR UPDATE
October 20, 2007 By 51 Comments
… TR1 – SELECT NAME FROM USERS WHERE NAME LIKE “%Heikki%” LOCK IN SHARE MODE TR1 – END If the DELETE statement of TR1 would not lock all records… the 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…
