On Wed, May 6, 2020 at 1:06 PM Alvaro Herrera <alvhe...@2ndquadrant.com> wrote: > Good question. I agree that BRIN summarization is not at all related to > what other index AMs do during the cleanup phase. However, if the > index_cleanup feature is there to make it faster to process a table > that's nearing wraparound hazards (or at least the warnings), then I > think it makes sense to complete the vacuum as fast as possible -- which > includes not trying to summarize it for brin indexes.
I forgot about the fact that the AutoVacuumRequestWork() interface exists at all until just now. That's how "autosummarize = on" makes sure that autosummarization takes place. These work items are not affected by the fact that the VACUUM happens to be a "index_cleanup off" VACUUM. Fortunately, the user is required to explicitly opt-in to autosummarization (by setting "autosummarize = on") in order for autovacuum to spend extra time processing work items when it might be important to advance relfrozenxid ASAP. (My initial assumption was that the autosummarization business happened within brinvacuumcleanup(), but I now see that I was mistaken.) There is a separate question (nothing to do with summarization) about the cleanup steps performed in brinvacuumcleanup(), which are unlike any of the cleanup/maintenance that we expect for an amvacuumcleanup routine in general. As I said in my last e-mail, these steps have nothing to do with garbage tuples. Rather, it's deferred maintenance that we need to do even with append-only workloads (including when autosummarization has not been enabled). What about that? Is that okay? ISTM that the fundamental issue is that BRIN imagines that it is in control, which isn't quite true in light of the "index_cleanup off" stuff -- a call to brinvacuumcleanup() is expected to take place at fairly consistent intervals to take care of revmap processing, which, in general, might not happen now. I blame commit a96c41feec6 for this, not BRIN. ISTM that whatever behavior we deem appropriate, the proper place to decide on it is within BRIN. Not within vacuumlazy.c. -- Peter Geoghegan
