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From: Dave Cramer <pg@fastcrypt.com>
Subject: Re: High update activity, PostgreSQL vs BigDBMS
Date: Sun, 7 Jan 2007 10:29:02 -0500
To: Guy Rouillier <guyr-ml1@burntmail.com>


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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