Re: Proposal for CSN based snapshots

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