Обсуждение: Context switching
Hi,
We've migrated one of our servers from pg 7.4 to 8.1 and from times to times (4 hours) the server start doing a lot of context switching and all transactions become very slow.
The average context switching for this server as vmstat shows is 1 but when the problem occurs it goes to 250000.
CPU and memory usage are ok.
What can produce this context switching storms?
It is a box with 12GB RAM and 4 processors running RedHat Enterprise Linux AS.
Thank you in advance!
Reimer
carlos.reimer@opendb.com.br
OpenDB Serviços e Treinamentos PostgreSQL e DB2
Fone: 47 3327-0878 Cel: 47 9602-0151
www.opendb.com.br
Hi,
Sorry, but this message was already post some days before!
Thank you!
Carlos
-----Mensagem original-----
De: pgsql-performance-owner@postgresql.org [mailto:pgsql-performance-owner@postgresql.org]Em nome de Carlos H. Reimer
Enviada em: quarta-feira, 1 de novembro de 2006 03:23
Para: pgsql-performance@postgresql.org
Assunto: [PERFORM] Context switching
De: pgsql-performance-owner@postgresql.org [mailto:pgsql-performance-owner@postgresql.org]Em nome de Carlos H. Reimer
Enviada em: quarta-feira, 1 de novembro de 2006 03:23
Para: pgsql-performance@postgresql.org
Assunto: [PERFORM] Context switching
Hi,We've migrated one of our servers from pg 7.4 to 8.1 and from times to times (4 hours) the server start doing a lot of context switching and all transactions become very slow.The average context switching for this server as vmstat shows is 1 but when the problem occurs it goes to 250000.CPU and memory usage are ok.What can produce this context switching storms?It is a box with 12GB RAM and 4 processors running RedHat Enterprise Linux AS.Thank you in advance!Reimer
carlos.reimer@opendb.com.br
OpenDB Serviços e Treinamentos PostgreSQL e DB2
Fone: 47 3327-0878 Cel: 47 9602-0151
www.opendb.com.br
Carlos, > We've migrated one of our servers from pg 7.4 to 8.1 and from times to > times (4 hours) the server start doing a lot of context switching and all > transactions become very slow. > > The average context switching for this server as vmstat shows is 1 but when > the problem occurs it goes to 250000. Context Switching is a symptom rather than a cause. What's most likely happening is that you have a combined heavy-CPU and heavy-IO workload, so you have bursts of CPU activity stalled by iowaits. Can you check the rate of iowaits during the "storm" periods? Also, is this Xeon? And are you saying that you *didn't* have this issue under 7.4? -- Josh Berkus PostgreSQL @ Sun San Francisco
Hi, I have not seen the iowaits numbers and yes, it is a xeon, four processors. With the 7.4 version the problem did not exist but I think Tom Lane cleared why this behavior with 8.0 and 8.1 versions inhttp://archives.postgresql.org/pgsql-performance/2006-11/msg00050.php Reimer > -----Mensagem original----- > De: Josh Berkus [mailto:josh@agliodbs.com] > Enviada em: terça-feira, 7 de novembro de 2006 15:42 > Para: pgsql-performance@postgresql.org; carlos.reimer@opendb.com.br > Assunto: Re: [PERFORM] Context switching > > > Carlos, > > > We've migrated one of our servers from pg 7.4 to 8.1 and from times to > > times (4 hours) the server start doing a lot of context > switching and all > > transactions become very slow. > > > > The average context switching for this server as vmstat shows > is 1 but when > > the problem occurs it goes to 250000. > > Context Switching is a symptom rather than a cause. What's most likely > happening is that you have a combined heavy-CPU and heavy-IO > workload, so you > have bursts of CPU activity stalled by iowaits. > > Can you check the rate of iowaits during the "storm" periods? > > Also, is this Xeon? And are you saying that you *didn't* have > this issue > under 7.4? > > -- > Josh Berkus > PostgreSQL @ Sun > San Francisco > >