Re: Having performance problems.

How many rows are you expecting to be returned?

At 10:27 AM 4/4/2005, eanxgeek@comcast.net wrote:
>First let me start by saying I am pretty new to Postgresql.  To date I
>have only worked with small databases, I now have a database that isn't
>big but is big enough to create performance issues.  The database is
>roughly 450 MB.    I have two tables of interest; logs and hosts.  At one
>point I had the following sql:
>
>  SELECT * FROM hosts, logs where (logs.host_id = hosts.host_id) ORDER BY
> date DESC, time DESC;
>
>This took over 1000 seconds to execute.
>
>I then upgraded to PGSQL 8.0.1 and created tablespace logs_t and hosts_t,
>these are on separate controllers and separate disks.
>            List of tablespaces
>Name    |  Owner   |    Location
>------------+----------+-----------------
>  hosts_t    | postgres | /pgdata/hosts_t
>  logs_t     | postgres | /pgdata/logs_t
>
>I then altered the tables logs and hosts to use the new tablespace
>respectively and I changed the sql to read:
>
>SELECT hostname,facility,priority,level,tag,date,time,program,msg,seq FROM
>hosts, logs where (logs.host_id = hosts.host_id) ORDER BY date DESC, time DESC;
>
>Under 7.x my PGDATA was on /pgdata; however, for 8.x I have left it in in
>its default location of /var/lib/pgsql.  So what is happening now is:
>1. I am still seeing all 4x700 MHz CPUs go to 95%+ IOWAIT, appears that
>/var is the hardest hit.
>2. SELECT hostname,facility,priority,level,tag,date,time,program,msg,seq
>FROM hosts, logs where (logs.host_id = hosts.host_id); works but takes
>awhile; however, adding the ORDER BY condition causes the SQL to execute
>to the point that /var becomes full and the SQL exits with:
>ERROR:  could not write block 81940 of temporary file: No space left on device
>HINT:  Perhaps out of disk space?
>
>What parameters can I start "tweaking" and what can I do to addres the
>issue of /var filling up?  Below are some of my kernel and database settings:
>
>effective_cache_size           | 1000
>maintenance_work_mem           | 16384
>max_connections                | 32
>shared_buffers                 | 64
>------ Shared Memory Segments --------
>key        shmid      owner      perms      bytes      nattch     status
>0x0052e2c1 38043648   postgres  600        1540096    2
>
>
>
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