On Tue, Mar 07, 2023 at 12:39:13PM +0530, Bharath Rupireddy wrote: > On Tue, Mar 7, 2023 at 3:30 AM Nathan Bossart <nathandboss...@gmail.com> > wrote: >> Is it possible to memcpy more than a page at a time? > > It would complicate things a lot there; the logic to figure out the > last page bytes that may or may not fit in the whole page gets > complicated. Also, the logic to verify each page's header gets > complicated. We might lose out if we memcpy all the pages at once and > start verifying each page's header in another loop.
Doesn't the complicated logic you describe already exist to some extent in the patch? You are copying a page at a time, which involves calculating various addresses and byte counts. >> + elog(DEBUG1, "read %zu bytes out of %zu bytes from WAL buffers for >> given LSN %X/%X, Timeline ID %u", >> + *read_bytes, count, LSN_FORMAT_ARGS(startptr), tli); >> >> I definitely don't think we should put an elog() in this code path. >> Perhaps this should be guarded behind WAL_DEBUG. > > Placing it behind WAL_DEBUG doesn't help users/developers. My > intention was to let users know that the WAL read hit the buffers, > it'll help them report if any issue occurs and also help developers to > debug that issue. I still think an elog() is mighty expensive for this code path, even when it doesn't actually produce any messages. And when it does, I think it has the potential to be incredibly noisy. -- Nathan Bossart Amazon Web Services: https://aws.amazon.com
