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Re: [PERFORM] Re: [PERFORM] 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?



On Thu, Mar 1, 2012 at 10:13 PM, Tomas Vondra <tv@xxxxxxxx> wrote:
>
> Maybe. I still am not sure how fsync=off affects the eviction in your
> opinion. I think it does not (or just very remotely) and you were saying
> the opposite. IMHO the eviction of (dirty) buffers is either very fast
> or slow, no matter what the fsync setting is.

I was thinking page cleanup, but if you're confident it doesn't happen
on a read-only database, I'd have to agree on all your other points.

I have seen a small amount of writes on a read-only devel DB I work
with, though. Usually in the order of 100kb/s writes per 10mb/s reads
- I attributed that to page cleanup. In that case, it can add some
wait time to fsync, even though it's really a slow volume of writes.
If you're right, I'm thinking, it may be some other thing... atime
updates maybe, I'd have to check the filesystem configuration I guess.

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