Re: Re: [COMMITTERS] pgsql: Allow Pin/UnpinBuffer to operate in a lockfree manner.

Andres Freund <andres(at)anarazel(dot)de> 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