| From: | Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> |
|---|---|
| To: | Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com> |
| Cc: | "pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org> |
| Subject: | Re: How to reduce writing on disk ? (90 gb on pgsql_tmp) |
| Date: | 2015-06-03 19:24:45 |
| Message-ID: | 556F547D.5040206@2ndquadrant.com |
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| Thread: | |
| Lists: | pgsql-performance |
On 06/03/15 17:09, Scott Marlowe wrote:
> On Wed, Jun 3, 2015 at 8:56 AM, Tomas Vondra
>>
>>
>> I don't see why you think you have less than 3GB used. The output you posted
>> clearly shows there's only ~300MB memory free - there's 15GB shared buffers
>> and ~45GB of page cache (file system cache).
>
> Because you subtract cached from used to see how much real spare
> memory you have. The kernel will dump cached mem as needed to free up
> space for memory usage. So 64141-61761=2380MB used.
Well, except that 15GB of that is shared_buffers, and I wouldn't call
that 'free'. Also, I don't see page cache as entirely free - you
probably want at least some caching at this level.
In any case, even if all 64GB were free, this would not be enough for
the query that needs >95GB for temp files.
--
Tomas Vondra http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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