| From: | Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com> |
|---|---|
| To: | Greg Smith <greg(at)2ndquadrant(dot)com> |
| Cc: | pgsql-performance(at)postgresql(dot)org |
| Subject: | Re: SSD options, small database, ZFS |
| Date: | 2011-11-18 16:17:23 |
| Message-ID: | CAOR=d=14dTQpPsn7+rCw8WU+Um9u7cNt1xG1KGhqECnejcEktw@mail.gmail.com |
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| Thread: | |
| Lists: | pgsql-performance |
On Fri, Nov 18, 2011 at 3:09 AM, Greg Smith <greg(at)2ndquadrant(dot)com> wrote:
> On 11/17/2011 10:44 PM, CSS wrote:
>>
>> Is there any sort of simple documentation on the query planner that might
>> cover how things like increased RAM could impact how a query is executed?
>
> There is no *simple* documentation on any part of the query planner that's
> also accurate. Query planning is inherently complicated.
>
> I think this point wasn't quite made clearly. PostgreSQL has no idea how
> much memory is in your system; it doesn't try to guess or detect it.
effective_cache_size tells the db how much memory you have. Since you
have to set it, it can be anything you want, but if you've set it to
something much higher on the new machine then it can affect query
planning.
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