Jinyu <call_jinyu(at)126(dot)com> writes:
> Proposal: vacuum full table takes an ExclusiveLock on relation instead of AccessExclusiveLock at start. It can' block select statement before call function "finish_heap_swap". and select statement is safe because vacuum full table copys tuples from old relation to new relation before calling function "finish_heap_swap". But it must take an AccessExclusiveLock on relation when call function "finish_heap_swap" in order to block select statement on the same relation.
> This solution can improve the concurency. the following shows the reasons.
What it's more likely to do is cause the vacuum full to fail altogether,
after doing a lot of work. Lock upgrade is a bad thing because it tends
to result in deadlocks.
regards, tom lane