| From: | Claudio Freire <klaussfreire(at)gmail(dot)com> |
|---|---|
| To: | Bruce Momjian <bruce(at)momjian(dot)us> |
| Cc: | Josh Berkus <josh(at)agliodbs(dot)com>, Merlin Moncure <mmoncure(at)gmail(dot)com>, Jeff Janes <jeff(dot)janes(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: proposal: Set effective_cache_size to greater of .conf value, shared_buffers |
| Date: | 2013-09-11 18:08:25 |
| Message-ID: | CAGTBQpbu=njj9CMd224xdtLW=rZo-gkWO=i3k6G8u-TN51O8UQ@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Wed, Sep 11, 2013 at 12:27 PM, Bruce Momjian <bruce(at)momjian(dot)us> wrote:
>> > Another argument in favor: this is a default setting, and by default,
>> > shared_buffers won't be 25% of RAM.
>>
>> So, are you saying you like 4x now?
>
> Here is an arugment for 3x. First, using the documented 25% of RAM, 3x
> puts our effective_cache_size as 75% of RAM, giving us no room for
> kernel, backend memory, and work_mem usage. If anything it should be
> lower than 3x, not higher.
AFAIK, e_c_s must include shared_buffers, so 25% + 75% = 75%
And your statement seems to assume 25% + 75% = 100%. Which isn't
universally true, no matter what your math teacher probably taught you
;-)
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