Dirty read isolation level
Jay Walters asked whether switching queries from read committed to dirty read should make them faster. Madison Pruet noted dirty read can see rows being changed or deleted. Yuri Dovgart said the gain is small and isolation level can affect optimizer decisions through OPTCOMPIND. Reinhard Habichtsberg said it is faster only when committed read must wait on locks.
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Not exactly. You can also pick up rows that are in the process of being changed and/or deleted. Jay Walters wrote: > I've been playing around with changing some of my queries from read > committed to dirty read, and I'm wondering, the only difference here > should be not placing locks on the rows processed by the query, so it > can't go any slower right?
I've been playing around with changing some of my queries from read committed to dirty read, and I'm wondering, the only difference here should be not placing locks on the rows processed by the query, so it can't go any slower right?
Sorry, forgot to mention that part. My sense is that a query should run faster in dirty read isolation mode? I am trying to resolve some performance issues and just want to make sure I'm not barking up the wrong tree... Madison Pruet wrote: > Not exactly. You can also pick up rows that are in the process of being > changed and/or deleted. > > Jay Walters wrote: > > > I've been playing around with changing some of my queries from read > > committed to dirty read, and I'm wondering, the only difference here > > should be not placing locks on the rows processed by the query, so it > > can't go any slower right?
Jay Walters <jwalters@computer.org> wrote in message news:38510C70.4CAB2B94@computer.org... > Sorry, forgot to mention that part. My sense is that a query should run > faster in dirty read isolation mode? I am trying to resolve some > performance issues and just want to make sure I'm not barking up the wrong > tree... Just a little bit. Changing isolation levels is not the case for the performance tuning. Isolation levels sometimes has impact on the optimiser decisions ( choosing correct join type) depending on your OPTCOMPIND param. -- ------------------------------------------------- With best regards, Yuri Dovgart SAP R/3, Informix technical consultant, Informix Certified Professional, Senior System Consultant System Architecture and High Availability Systems, 'Telecominvest' company Email y_dovgart@tci.ukrtel.net ICQ 39284285
Jay Walters <jwalters@computer.org> schrieb in im Newsbeitrag: 38510C70.4CAB2B94@computer.org... > Sorry, forgot to mention that part. My sense is that a query should run > faster in dirty read isolation mode? I am trying to resolve some > performance issues and just want to make sure I'm not barking up the wrong > tree... > Dirty read isn´t faster than committed read except there are locks the committed read has to wait on.