Re: [HACKERS] Re: PANIC: invalid index offnum: 186 when processingBRIN indexes in VACUUM

Tom Lane wrote:

> I really don't understand how any of this "let's release the buffer
> lock and then take it back later" logic is supposed to work reliably.

So summarize_range first inserts the placeholder tuple, which is there
purposefully for other processes to update concurrently; then, without
blocking any other process, scan the page range and update the
placeholder tuple (this could take a long time, so it'd be a bad idea
to hold buffer lock for that long).

I think what we should do is rethink the locking considerations in
brin_doupdate vs. brinGetTupleForHeapBlock, and how they are used in
summarize_range and brininsert.  In summarize_range, instead of hoping
that in some cases we will not need to re-obtain the placeholder tuple,
just do that in all cases keeping the buffer locked until the tuple is
updated.

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services


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