Hi, I was just doing some cleanup on the main patch in this set and realized that it was missing a few things. One of which is forbidding the BUFFER_USAGE_LIMIT with VACUUM FULL since VACUUM FULL does not use a BAS_VACUUM strategy.
VACUUM FULL technically uses a bulkread buffer access strategy for reading the original relation if its number of blocks is > number of shared buffers / 4 (see initscan()). The new rel writing is done using smgrextend/write directly and doesn't go through shared buffers. I think it is a stretch to try and use the size passed in to VACUUM by BUFFER_USAGE_LIMIT for the bulkread strategy ring. As for forbidding the combination, I noticed that when VACUUM FULL is specified with INDEX_CLEANUP OFF, there is no syntax error but the INDEX_CLEANUP option is simply ignored. This is documented behavior. I somehow feel like VACUUM (FULL, BUFFER_USAGE_LIMIT 'x') should error out instead of silently not using the buffer usage limit, though. I am looking for others' opinions. - Melanie
