Re: [HACKERS] WAL logging problem in 9.4.3?

At Tue, 27 Aug 2019 15:49:32 +0900 (Tokyo Standard Time), Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com> wrote in <20190827(dot)154932(dot)250364935(dot)horikyota(dot)ntt(at)gmail(dot)com>
> 128GB shared buffers contain 16M buffers. On my
> perhaps-Windows-Vista-era box, such loop takes 15ms. (Since it
> has only 6GB, the test is ignoring the effect of cache that comes
> from the difference of the buffer size). (attached 1)
...
> For a 16MB file, the cost of write-fsyncing cost is almost the
> same to that of WAL-emitting cost. It was about 200 ms on the
> Vista-era machine with non-performant rotating magnetic disks
> with xfs. (attached 2, 3) Although write-fsyncing of relation
> file makes no lock conflict with other backends, WAL-emitting
> delays other backends' commits at most by that milliseconds.

FWIW, the attached are the programs I used to take the numbers.

testloop.c: to take time to loop over buffers in FlushRelationBuffers

testfile.c: to take time to sync a heap file. (means one file for the size)

testfile2.c: to take time to emit a wal record. (means 16MB per file)

regards.

--
Kyotaro Horiguchi
NTT Open Source Software Center