Reduce memory consumption for pending invalidation messages.
The existing data structures in inval.c are fairly inefficient for
the common case of a command or subtransaction that registers a small
number of cache invalidation events. While this doesn't matter if we
commit right away, it can build up to a lot of bloat in a transaction
that contains many DDL operations. By making a few more assumptions
about the expected use-case, we can switch to a representation using
densely-packed arrays. Although this eliminates some data-copying,
it doesn't seem to make much difference time-wise. But the space
consumption decreases substantially.
Patch by me; thanks to Nathan Bossart for review.
Discussion: https://postgr.es/m/
2380555.
1622395376@sss.pgh.pa.us