| From: | Andres Freund <andres(at)anarazel(dot)de> |
|---|---|
| To: | Heikki Linnakangas <hlinnaka(at)iki(dot)fi> |
| Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Alexander Korotkov <a(dot)korotkov(at)postgrespro(dot)ru>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Dilip Kumar <dilipbalaut(at)gmail(dot)com>, Jeff Davis <pgsql(at)j-davis(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Greg Stark <stark(at)mit(dot)edu>, Andres Freund <andres(at)2ndquadrant(dot)com>, Rajeev rastogi <rajeev(dot)rastogi(at)huawei(dot)com>, Markus Wanner <markus(at)bluegap(dot)ch>, Ants Aasma <ants(at)cybertec(dot)at>, Bruce Momjian <bruce(at)momjian(dot)us>, obartunov <obartunov(at)postgrespro(dot)ru>, Teodor Sigaev <teodor(at)postgrespro(dot)ru> |
| Subject: | Re: Proposal for CSN based snapshots |
| Date: | 2016-08-22 17:38:52 |
| Message-ID: | 20160822173852.ivt5to662zoc5rfs@alap3.anarazel.de |
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| Lists: | pgsql-hackers |
Hi,
On 2016-08-22 20:32:42 +0300, Heikki Linnakangas wrote:
> I ran some quick pgbench tests on my laptop, but didn't see any meaningful
> benefit. I think the best I could see is about 5% speedup, when running
> "pgbench -S", with 900 idle connections sitting in the background. On the
> positive side, I didn't see much slowdown either. (Sorry, I didn't record
> the details of those tests, as I was testing many different options and I
> didn't see a clear difference either way.)
Hm. Does the picture change if those are idle in transaction, after
assigning an xid.
> It seems that Amit's PGPROC batch clearing patch was very effective.
It usually breaks down if you have a mixed read/write workload - might
be worthehile prototyping that.
> I
> remember seeing ProcArrayLock contention very visible earlier, but I can't
> hit that now. I suspect you'd still see contention on bigger hardware,
> though, my laptop has oly 4 cores. I'll have to find a real server for the
> next round of testing.
Yea, I think that's true. I can just about see ProcArrayLock contention
on my more powerful laptop, to see it really bad you need bigger
hardware / higher concurrency.
Greetings,
Andres Freund
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