Andres Freund <> writes:
>>> The issue is likely that either Alexander or I somehow made
>>> MarkLocalBufferDirty() use pg_atomic_fetch_or_u32(), instead of the
>>> proper pg_atomic_read_u32()/pg_atomic_write_u32().

> Ok, so the theory above fits.

Yah, especially in view of localbuf.c:297 ;-)

> Will fix (both initialization and use of pg_atomic_fetch_or_u32), and
> expand the documentation on why only atomic read/write are supposed to
> be used.

FWIW, I'd vote against adding a SpinLockInit there.  What it would mostly
do is prevent noticing future mistakes of the same ilk.  It would be
better no doubt if we didn't have to rely on a nearly-dead platform
to detect this; but having such detection of a performance bug is better
than having no detection.

                        regards, tom lane

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