Re: How to

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On 06/02/2011 17:30, Kevin Grittner wrote:
> Guy Deleeuw  wrote:
>
> My hardware : lapto hp envy I7 processor with a ssd disk
>
>> Memory :
>>                      total    used     free shared buffers cached
>> Mem:               8129356 2866516  5262840      0  387172 948132
>> -/+ buffers/cache:         1531212  6598144
>> Swap:             15625208       0 15625208
>
> It looks like everything you're running, including caching the entire
> database, or at least the active part of it, fits in less than 3 GB
> on your 8 GB machine.
>
>> shared_buffers = 24MB
>
> Given your hardware, I would bump that to 2GB or so.
>
> I would also set effective_cache_size to 7GB.

Here I think it is too much because when the 2 GB of shared memory will
be used, only 6 GB of RAM will be left and maybe not entirely used for
file system cache. My way to find effective_cache_size value is to put
it to 50% of the amount of ram, drop the cache after tuning, leaving the
server live for a while and have a look at the output of free to find
the final value.

> I would set work_mem
> to at *least* 50MB; if you're only using a few connections, you could
> easily bump that to 100MB to 200MB.  Fully cached, especially if it's
> all on PostgreSQL shared memory, seq_page_cost and random_page_cost
> both to 0.05.  Between the SSD and having all data in shared memory,
> you might want to go even lower.  There is some other general tuning
> to be done, but the above will make the most difference for read-only
> queries, which is what you're asking about.
>
> [nested views, using subqueries]
>
> You should probably look at reqorking the v_stock view to use joins
> instead of subqueries -- they often optimize much better.
>
> I didn't spend a lot of time with the EXPLAIN ANALYZE output, because
> if you configure PostgreSQL to get costing factors more in line with
> actual costs for that hardware, you're likely to see totally
> different plans.  And I can pretty much guarantee that if you tune
> the costs *and* rework that view to use JOINs, you'll get completely
> different plans which will perform *much* better.
>
> I hope this helps.
>
> -Kevin
>

- --
Nicolas Thauvin
DBA
http://www.dalibo.com
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=Rdav
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