Re: locks in CREATE TRIGGER, ADD FK

Neil Conway wrote:
> So I think it should be possible to lock both the heap relation and the
> index with ExclusiveLock, which would allow SELECTs on them. This would
> apply to both the single relation and multiple relation variants of
> CLUSTER (since we do each individual clustering in its own transaction).
>
> ... except that when we rebuild the relation's indexes, we acquire an
> AccessExclusiveLock on the index. This would introduce the risk of
> deadlock. It seems necessary to acquire an AccessExclusiveLock when
> rebuilding shared indexes, since we do the index build in-place, but I
> think we can get by with an ExclusiveLock in the non-shared case, for
> similar reasons as above: we build the new index and then swap relfilenodes.

Certainly we need to upgrade to an exclusive table lock to replace the
heap table. Do we want to get a shared lock and possibly starve waiting
for an exclusive lock on the table to swap the new one in? Do we do
such escallation anywhere else?

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