Re: High update activity, PostgreSQL vs BigDBMS

On 6-Jan-07, at 11:32 PM, Guy Rouillier wrote:

> Dave Cramer wrote:
>
>>>
>>> The box has 3 GB of memory.  I would think that BigDBMS would be
>>> hurt by this more than PG.  Here are the settings I've modified
>>> in postgresql.conf:
>> As I said you need to set shared_buffers to at least 750MB this is
>> the starting point, it can actually go higher. Additionally
>> effective cache should be set to 2.25 G turning fsync is not a
>> real world situation. Additional tuning of file systems can
>> provide some gain, however as Craig pointed out some queries may
>> need to be tweaked.
>
> Dave, thanks for the hard numbers, I'll try them.  I agree turning
> fsync off is not a production option.  In another reply to my
> original posting, Alex mentioned that BigDBMS gets an advantage
> from its async IO.  So simply as a test, I turned fsync off in an
> attempt to open wide all the pipes.
>
> Regarding shared_buffers=750MB, the last discussions I remember on
> this subject said that anything over 10,000 (8K buffers = 80 MB)
> had unproven benefits.  So I'm surprised to see such a large value
> suggested.  I'll certainly give it a try and see what happens.

That is 25% of your available memory. This is just a starting point.
There are reports that going as high as 50% can be advantageous,
however you need to measure it yourself.

>
>>>
>>> autovacuum=on
>>> stats_row_level = on
>>> max_connections = 10
>>> listen_addresses = 'db01,localhost'
>>> shared_buffers = 128MB
>>> work_mem = 16MB
>>> maintenance_work_mem = 64MB
>>> temp_buffers = 32MB
>>> max_fsm_pages = 204800
>>> checkpoint_segments = 30
>>> redirect_stderr = on
>>> log_line_prefix = '%t %d'
> --
> Guy Rouillier
>
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