On Sat, Jan 27, 2024 at 1:04 AM Jeff Davis <pg...@j-davis.com> wrote: > > All of these things are functionally equivalent -- the same thing is > happening at the end. This is just a discussion about API style and how > that will interact with hypothetical callers that don't exist today. > And it can also be easily changed later, so we aren't stuck with > whatever decision happens here.
I'll leave that up to you. I'm okay either ways - 1) ensure the caller doesn't use XLogReadFromBuffers, 2) XLogReadFromBuffers returning as-if nothing was read when in recovery or on a different timeline. > > Imagine, implementing an extension (may be for fun or learning or > > educational or production purposes) to read unflushed WAL directly > > from WAL buffers using XLogReadFromBuffers as page_read callback with > > xlogreader facility. > > That makes sense, I didn't realize you intended to use this fron an > extension. I'm fine considering that as a separate patch that could > potentially be committed soon after this one. Yes, I've turned that into 0002 patch. > I'd like some more details, but can I please just commit the basic > functionality now-ish? +1. > > Tried to keep wal_writer quiet with wal_writer_delay=10000ms and > > wal_writer_flush_after = 1GB to not to flush WAL in the background. > > Also, disabled autovacuum, and set checkpoint_timeout to a higher > > value. All of this is done to generate minimal WAL so that WAL > > buffers > > don't get overwritten. Do you see any problems with it? > > Maybe check it against pg_current_wal_lsn(), and see if the Write > pointer moved ahead? Perhaps even have a (limited) loop that tries > again to catch it at the right time? Adding a loop seems to be reasonable here and done in v21-0003. Also, I've added wal_level = minimal per src/test/recovery/t/039_end_of_wal.pl introduced by commit bae868caf22 which also tries to keep WAL activity to minimum. > > Can the WAL summarizer ever read the WAL on current TLI? I'm not so > > sure about it, I haven't explored it in detail. > > Let's just not call XLogReadFromBuffers from there. Removed. PSA v21 patch set. -- Bharath Rupireddy PostgreSQL Contributors Team RDS Open Source Databases Amazon Web Services: https://aws.amazon.com
v21-0001-Add-XLogReadFromBuffers.patch
Description: Binary data
v21-0002-Allow-XLogReadFromBuffers-to-wait-for-in-progres.patch
Description: Binary data
v21-0003-Add-test-module-for-verifying-WAL-read-from-WAL-.patch
Description: Binary data
v21-0004-Use-XLogReadFromBuffers-in-more-places.patch
Description: Binary data
