On Sat, Nov 4, 2023 at 1:17 AM Jeff Davis <pg...@j-davis.com> wrote: > > > > I think it needs something like: > > > > > > pg_atomic_write_u64(&XLogCtl->xlblocks[nextidx], > > > InvalidXLogRecPtr); > > > pg_write_barrier(); > > > > > > before the MemSet. > > > > I think it works. First, xlblocks needs to be turned to an array of > > 64-bit atomics and then the above change. > > Does anyone see a reason we shouldn't move to atomics here? > > > > > pg_write_barrier(); > > > > *((volatile XLogRecPtr *) &XLogCtl->xlblocks[nextidx]) = > > NewPageEndPtr; > > I am confused why the "volatile" is required on that line (not from > your patch). I sent a separate message about that: > > https://www.postgresql.org/message-id/784f72ac09061fe5eaa5335cc347340c367c73ac.ca...@j-davis.com > > > I think the 3 things that helps read from WAL buffers without > > WALBufMappingLock are: 1) couple of the read barriers in > > XLogReadFromBuffers, 2) atomically initializing xlblocks[idx] to > > InvalidXLogRecPtr plus a write barrier in AdvanceXLInsertBuffer(), 3) > > the following sanity check to see if the read page is valid in > > XLogReadFromBuffers(). If it sounds sensible, I'll work towards > > coding > > it up. Thoughts? > > I like it. I think it will ultimately be a fairly simple loop. And by > moving to atomics, we won't need the delicate comment in > GetXLogBuffer().
I'm attaching the v15 patch set implementing the above ideas. Please have a look. -- Bharath Rupireddy PostgreSQL Contributors Team RDS Open Source Databases Amazon Web Services: https://aws.amazon.com
v15-0001-Use-64-bit-atomics-for-xlblocks-array-elements.patch
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v15-0002-Allow-WAL-reading-from-WAL-buffers.patch
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v15-0003-Add-test-module-for-verifying-WAL-read-from-WAL-.patch
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