Re: Slow query + why bitmap index scan??

On 2011-01-12 15:36, Kevin Grittner wrote:
> Laszlo Nagy<gandalf@shopzeus.com>  wrote:
>
>> shared_mem = 6GB
>> work_mem = 512MB
>> total system memory=24GB
>
> In addition to the good advice from Ken, I suggest that you set
> effective_cache_size (if you haven't already).  Add whatever the OS
> shows as RAM used for cache to the shared_mem setting.
It was 1GB. Now I changed to 2GB. Although the OS shows 9GB inactive
memory, we have many concurrent connections to the database server. I
hope it is okay to use 2GB.
>
> But yeah, for your immediate problem, if you can cluster the table
> on the index involved, it will be much faster.  Of course, if the
> table is already in a useful order for some other query, that might
> get slower, and unlike some other products, CLUSTER in PostgreSQL
> doesn't *maintain* that order for the data as new rows are added --
> so this should probably become a weekly (or monthly or some such)
> maintenance operation.
Thank you! After clustering, queries are really fast. I don't worry
about other queries. This is the only way we use this table - get
details for a given id value. I put the CLUSTER command into a cron
script that runs daily. For the second time, it took 2 minutes to run so
I guess it will be fine.

Thank you for your help.

    Laszlo