From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
---|---|
To: | Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> |
Cc: | Michael Paquier <michael(dot)paquier(at)gmail(dot)com>, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: [PATCH] 2PC state files on shared memory |
Date: | 2009-08-08 15:29:05 |
Message-ID: | 15725.1249745345@sss.pgh.pa.us |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-hackers |
Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> writes:
> Tom Lane wrote:
>> Quite aside from that, the fixed size of shared memory makes this seem
>> pretty impractical.
> Most state files are small. If one doesn't fit in the area reserved for
> this, it's written to disk as usual. It's just an optimization.
What evidence do you have for that assumption? And what's "small" anyway?
I think setting the size parameter for this would be a frightfully
difficult problem; the fact that average installations wouldn't use it
doesn't make that any better for those who would. After our bad
experiences with fixed-size FSM, I'm pretty wary of introducing new
fixed-size structures that the user is expected to figure out how to
size.
> I'm a bit disappointed by the performance gains. I would've expected
> more, given a decent battery-backed-up cache to buffer the WAL fsyncs.
> But it looks like they're still causing the most overhead, even with a
> battery-backed-up cache.
If you can't demonstrate order-of-magnitude speedups, I think we
shouldn't touch this.
regards, tom lane
From | Date | Subject | |
---|---|---|---|
Next Message | Tom Lane | 2009-08-08 15:43:07 | Re: [PATCH] 2PC state files on shared memory |
Previous Message | Bruce Momjian | 2009-08-08 14:10:36 | Re: Alpha releases: How to tag |