| From: | Andres Freund <andres(at)anarazel(dot)de> |
|---|---|
| To: | pgsql-performance(at)postgresql(dot)org |
| Cc: | "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov>, "Bruce Momjian" <bruce(at)momjian(dot)us>, "Greg Smith" <greg(at)2ndquadrant(dot)com>, jd(at)commandprompt(dot)com, "Scott Marlowe" <scott(dot)marlowe(at)gmail(dot)com>, "Steve Crawford" <scrawford(at)pinpointresearch(dot)com>, "Ben Chobot" <bench(at)silentmedia(dot)com> |
| Subject: | Re: BBU Cache vs. spindles |
| Date: | 2010-10-21 20:18:09 |
| Message-ID: | 201010212218.09609.andres@anarazel.de |
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| Lists: | pgsql-performance pgsql-www |
On Thursday 21 October 2010 21:42:06 Kevin Grittner wrote:
> Bruce Momjian <bruce(at)momjian(dot)us> wrote:
> > I assume we send a full 8k to the controller, and a failure during
> > that write is not registered as a write.
>
> On what do you base that assumption? I assume that we send a full
> 8K to the OS cache, and the file system writes disk sectors
> according to its own algorithm. With either platters or BBU cache,
> the data is persisted on fsync; why do you see a risk with one but
> not the other?
At least on linux pages can certainly get written out in < 8kb batches if
youre under memory pressure.
Andres
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