This patch is a no-op patch which is intended to reduce the chances
of failures of omission once the functional part of the "snapshot
too old" patch goes in. It adds parameters for snapshot, relation,
and an enum to specify whether the snapshot age check needs to be
done for the page at this point. This initial patch passes NULL
for the first two new parameters and BGP_NO_SNAPSHOT_TEST for the
third. The follow-on patch will change the places where the test
needs to be made.
The code was supposing that rd_amcache wouldn't disappear from under it
during a scan; which is wrong. Copy the data out of the relcache rather
than trying to reference it there.
Looking at result of buildfarm member jaguarundi it seems to me that
BloomOptions isn't inited sometime, but I don't see yet how it's possible.
Nevertheless, check of signature length's is missed, so, add
a limit of it. Also add missed GenericXLogAbort() in case of already
deleted page in vacuum + minor code refactoring.
Module provides new access method. It is actually a simple Bloom filter
implemented as pgsql's index. It could give some benefits on search
with large number of columns.
Module is a single way to test generic WAL interface committed earlier.
Author: Teodor Sigaev, Alexander Korotkov
Reviewers: Aleksander Alekseev, Michael Paquier, Jim Nasby
