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


Andres Freund

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