From: | Andres Freund <andres(at)anarazel(dot)de> |
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To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Masahiko Sawada <masahiko(dot)sawada(at)2ndquadrant(dot)com>, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Michael Paquier <michael(at)paquier(dot)xyz>, Mithun Cy <mithun(dot)cy(at)enterprisedb(dot)com>, Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: [HACKERS] Moving relation extension locks out of heavyweight lock manager |
Date: | 2020-02-14 16:47:18 |
Message-ID: | 20200214164718.bzk4ybkueqkqx6yn@alap3.anarazel.de |
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Lists: | pgsql-hackers |
Hi,
On 2020-02-14 09:42:40 -0500, Tom Lane wrote:
> In the second place, it's ludicrous to expect that the underlying
> platform/filesystem can support an infinite number of concurrent
> file-extension operations. At some level (e.g. where disk blocks
> are handed out, or where a record of the operation is written to
> a filesystem journal) it's quite likely that things are bottlenecked
> down to *one* such operation at a time per filesystem.
That's probably true to some degree from a theoretical POV, but I think
it's so far from where we are at, that it's effectively wrong. I can
concurrently extend a few files at close to 10GB/s on a set of fast
devices below a *single* filesystem. Whereas postgres bottlenecks far
far before this. Given that a lot of today's storage has latencies in
the 10-100s of microseconds, a journal flush doesn't necessarily cause
that much serialization - and OS journals do group commit like things
too.
Greetings,
Andres Freund
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