Re: OOM in spgist insert

On 2021-May-13, Tom Lane wrote:

> BTW, another nasty thing I discovered while testing this is that
> the CHECK_FOR_INTERRUPTS() at line 2146 is useless, because
> we're holding a buffer lock there so InterruptHoldoffCount > 0.
> So once you get into this loop you can't even cancel the query.
> Seems like that needs a fix, too.

This comment made me remember a patch I've had for a while, which splits
the CHECK_FOR_INTERRUPTS() definition in two -- one of them is
INTERRUPTS_PENDING_CONDITION() which let us test the condition
separately; that allows the lock we hold to be released prior to
actually processing the interrupts.

The btree code modified was found to be an actual problem in production
when a btree is corrupted in such a way that vacuum would get an
infinite loop. I don't remember the exact details but I think we saw
vacuum running for a couple of weeks, and had to restart the server in
order to terminate it (since it wouldn't respond to signals).

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