Re: [HACKERS] Moving relation extension locks out of heavyweight lock manager

Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> writes:
> I think MaxBackends will generally limit the number of different
> relations that can simultaneously extend, but maybe tables with many
> partitions might change the situation. You are right that some tests
> might suggest a good number, let Mahendra write a patch and then we
> can test it. Do you have any better idea?

In the first place, there certainly isn't more than one extension
happening at a time per backend, else the entire premise of this
thread is wrong. Handwaving about partitions won't change that.

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. So I'm not
that concerned about occasional false-sharing limiting our ability
to issue concurrent requests. There are probably worse restrictions
at lower levels.

regards, tom lane