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Re: [PERFORM] Re: [PERFORM] Re: 回复: [PERFORM] PG as in-memory db? How to warm up and re-populate buffers? How to read in all tuples into memory?

From: "Tomas Vondra" <tv(at)fuzzy(dot)cz>
To: "Claudio Freire" <klaussfreire(at)gmail(dot)com>
Cc: "Stefan Keller" <sfkeller(at)gmail(dot)com>, "Wales Wang" <wormwang(at)yahoo(dot)com>, "Jeff Janes" <jeff(dot)janes(at)gmail(dot)com>, "pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org>, "Stephen Frost" <sfrost(at)snowman(dot)net>
Subject: Re: [PERFORM] Re: [PERFORM] Re: 回复: [PERFORM] PG as in-memory db? How to warm up and re-populate buffers? How to read in all tuples into memory?
Date: 2012-02-28 13:38:57
Message-ID: 8da9b15646d973a5ee23ba49faeee8fd.squirrel@sq.gransy.com (view raw or flat)
Thread:
Lists: pgsql-performance
On 28 Únor 2012, 14:08, Claudio Freire wrote:
> On Tue, Feb 28, 2012 at 5:30 AM, Stefan Keller <sfkeller(at)gmail(dot)com> wrote:
>>
>> But what I'm finally after is a solution, where records don't get
>> pushed back to disk a.s.a.p. but rather got hold in memory as long as
>> possible assuming that there is enough memory.
>
> fsync = off ?

I don't think this is a viable idea, unless you don't care about the data.

Moreover, "fsyn=off" does not mean "not writing" and writing does not mean
"removing from shared buffers". A page written/fsynced during a checkpoint
may stay in shared buffers.

AFAIK the pages are not removed from shared buffers without a reason. So a
dirty buffer is written to a disk (because it needs to, to keep ACID) but
stays in shared buffers as "clean" (unless it was written by a backend,
which means there's not enough memory).

Tomas


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