Re: More shared_buffers instead of effective_cache_size?

On Thu, Sep 4, 2008 at 1:24 PM, Ulrich <ulrich(dot)mierendorff(at)gmx(dot)net> wrote:
> Hi,
> I have a virtual server with 256 MB of RAM. I am using it as a webserver,
> mailserver and for postgres. So there is something like 150MB left for
> postgres.
>
> Here are my configs (I haven't benchmarked...)
> max_connections = 12 (I think, I will not have more parallel connections,
> because I only have 10 PHP worker threads)
> shared_buffers = 24MB
> work_mem = 1MB
> maintenance_work_mem = 16MB
>
> (effective_cache_size = 80MB)
>
> Normally, the file-cache is part of the free ram. But on my virtual server,
> it looks like if there is one big file cache for the whole hardware node and
> I do not have my own reserved cached, so it is not easy to find a good value
> for effective_cache_size.
>
> I've also benchmarked the file-cache using dd (100MB file)
>
> 1. Read from HDD:
> 104857600 bytes (105 MB) copied, 8.38522 seconds, 12.5 MB/s
> 2. Read from Cache:
> 104857600 bytes (105 MB) copied, 3.48694 seconds, 30.1 MB/s
>
> That is really really slow (10 times slower than on my other machine).
>
> What would you do now? Increasing shared_buffers to 100MB and setting
> effective_cache_size to 0MB? Or increasing effective_cache_size, too?

Stop using a virtual server? I wouldn't set shared_buffers that high
just because things like vacuum and sorts need memory too.

>
> Thanks for help.
>
> Regards,
> -Ulrich
>
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