From: | Andres Freund <andres(at)anarazel(dot)de> |
---|---|
To: | Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> |
Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Dilip Kumar <dilipbalaut(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Andres Freund <andres(at)2ndquadrant(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Relation extension scalability |
Date: | 2016-01-07 11:23:41 |
Message-ID: | 20160107112341.5md4r2237hvanoxw@alap3.anarazel.de |
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Lists: | pgsql-hackers |
On 2016-01-07 16:48:53 +0530, Amit Kapila wrote:
> What I could understand from above e-mail is that Dilip has tried to
> extend relation multiple-pages-at-a-time and observed that it gives
> comparable or better performance as compare to Andres's idea of
> lock-free extension and it doesn't regress the low-thread count case.
I think it's a worthwhile approach to pursue. But until it actually
fixes the problem of leaving around uninitialized pages I don't think
it's very meaningful to do performance comparisons.
> Now, I think here point to discuss is that there could be multiple-ways
> for extending a relation multiple-pages-at-a-time like:
>
> a. Extend the relation page by page and add it to FSM without initializing
> it. I think this is what the current patch of Dilip seems to be doing. If
> we
> want to go via this route, then we need to ensure that whenever we get
> the page from FSM, if it is empty and not initialised, then initialise
> it.
I think that's pretty much unacceptable, for the non-error path at
least.
One very simple, linux specific, approach would be to simply do
fallocate(FALLOC_FL_KEEP_SIZE) to extend the file, that way space is
pre-allocated, but not yet marked as allocated.
Greetings,
Andres Freund
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