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List:       postgresql-general
Subject:    Re: [GENERAL] my.cnf to postgresql.conf Conversion
From:       "scott.marlowe" <scott.marlowe () ihs ! com>
Date:       2002-10-31 22:46:59
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On 31 Oct 2002, Kevin Old wrote:

> Hello everyone,
> 
> I have a question about setting the variables in the postgresql.conf
> file.  I have the following settings in my my.cnf file for MySQL....and
> need to know which variables in the postgresql.conf file would
> correspond to the ones below, so that I may tune my system correctly.
> 
> set-variable    = key_buffer=384M
> set-variable    = max_allowed_packet=1M
> set-variable    = table_cache=64
> set-variable    = thread_stack=64K
> set-variable    = sort_buffer=2M
> set-variable    = record_buffer=2M
> set-variable    = thread_cache=8
> # Try number of CPU's*2 for thread_concurrency
> set-variable    = thread_concurrency=8
> set-variable    = myisam_sort_buffer_size=64M

Many of these have no direct 1 to 1 correlation to Postgresql.

the only ones that are pretty similar are sort_buffer and record_buffer.

The ones to look at changing are first are:

max_connections   (the default 32 is kinda small for some servers, but 
fine for departmental servers.  You may need to adjust fs.file-max in the 
kernel (I'm assuming linux here) if you go very high here.)

shared_buffers (These are measured in 8k blocks.  I've found anywhere from 
1000 to 20000 works well, anything over that tends to be a waste of 
memory for most servers.  Note you may need to adjust the settings for 
kernel.shmall and kernel.shmmax if you want this to be very high).

sort_mem  (bigger isn't always better here.  This is the amount of memory 
EACH sort operation will grab when it runs, and it seems to be that it 
will grab all of it whether it needs it or not, so be careful not to crank 
this up.  I've found that 2048 to 8192 are suitably large (it's measured 
in k I believe.)

fsync  (Setting this to false can more than double the speed of your 
database, while slightly increasing the chance that an unscheduled power 
down (i.e. a big dummy trips over your power cord kinda thing) but in my 
testing I've never lost data by pulling the plug when running with it set 
to false or true.)

then you can look at these settings.  they are used to tell the planner 
how to execute your query.

random_page_cost  (The default of 4 here is a bit high for most people.  1 
to 2 seems a more realistic setting for machines with a bit of memory 
where a lot of your result set may be cached.)

cpu_tuple_cost 
cpu_index_tuple_cost  (setting this lower makes the machine favor using 
indexes)
cpu_operator_cost

If you are gonna update thousands of rows at a time, look at increasing 
these settings, which will let the database recover vacuumed rows from 
tables that have had massive updates.

max_fsm_relations
#max_fsm_pages


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