Re: Postgresql performance degrading... how to diagnose the root cause

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> > I don't know that tcp-b does

>

> tpcb.jar is a java implementation of the http://www.tpc.org/tpcb/

> benchmark. It is not particularly representative of my workload, but

> gives a synthetic, db-agnostic, view of the system performance.

> We use it to have quick view to compare differents servers (different

> OS, different RDBMS, etc...).

 

For information, pgbench is a sort of limited TPC-B benchmark.

 

> That said, the test wil create tables, load them with data, and perform

> some transactions on them.

> The point that makes me wonder what happens, is that the test run on my

> main database is slow, while the same test run on a database on its own

> is quick.

 

Do you mean when you run it against already existing data vs its own TPC-B DB?

 

> This is the same postgresql cluster (same postgresql.conf), same

> tablespace (so same disks), same hardware obviously.

>

> Regarding the server activity, it seems quite flat : iostat shows that

> disks are not working much (less than 5%), top shows only one active

> core, and load average is well under 1...

>

> > http://wiki.postgresql.org/wiki/Show_database_bloat

>

> How do I interpret the output of this query ? Is 1.1 bloat level on a

> table alarming, or quite ok ?

 

quite ok. The threshold for maintenance task is around 20%.

I wonder about your system catalogs (pg_type, pg_attribute, ...)

 

You can use low level tool provided by PostgreSQL to help figure what's going wrong.

pg_buffercache, pg_stattuple come first to explore your cached data and the block content.

 

Or some weird database configuration ? (parameters in PostgreSQL can be set per DB, per role, etc...)

--

Cédric Villemain +33 (0)6 20 30 22 52

http://2ndQuadrant.fr/

PostgreSQL: Support 24x7 - Développement, Expertise et Formation

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