On Sat, Jan 14, 2023 at 12:34 PM Andres Freund <andres@anarazel.de> wrote:
Hi,
On 2023-01-14 00:48:52 -0800, Jeff Davis wrote: > On Mon, 2022-12-26 at 14:20 +0530, Bharath Rupireddy wrote: > > Please review the attached v2 patch further. > > I'm still unclear on the performance goals of this patch. I see that it > will reduce syscalls, which sounds good, but to what end? > > Does it allow a greater number of walsenders? Lower replication > latency? Less IO bandwidth? All of the above?
One benefit would be that it'd make it more realistic to use direct IO for WAL - for which I have seen significant performance benefits. But when we afterwards have to re-read it from disk to replicate, it's less clearly a win.
+1. Archive modules rely on reading the wal files for PITR. Direct IO for WAL requires reading these files from disk anyways for archival. However, Archiving using utilities like pg_receivewal can take advantage of this patch together with direct IO for WAL.
