Re: BRIN index and aborted transaction

Tatsuo Ishii wrote:

> When a transaction aborts, it seems a BRIN index leaves summary data
> which is not valid any more. Is this an expected behavior? I guess
> the answer is yes, because it does not affect correctness of a query
> result, but I would like to make sure.

You're right, that is not rolled back (just like any other index type,
actually).

> Second question is when the wrong summary data is gone? It seems
> vacuum does not help. Do I have to recreate the index (or reindex)?

Yeah, that's a bit of an open problem: we don't have any mechanism to
mark a block range as needing resummarization, yet. I don't have any
great ideas there, TBH. Some options that were discussed but never led
anywhere:

1. whenever a heap tuple is deleted that's minimum or maximum for a
column, mark the index tuple as needing resummarization. One a future
vacuuming pass the index would be updated. (I think this works for
minmax, but I don't see how to apply it to inclusion).

2. have block ranges be resummarized randomly during vacuum.

3. Have index tuples last for only X number of transactions, marking the
as needing summarization when that expires.

4. Have a user-invoked function that re-runs summarization. That way
the user can implement any of the above policies, or others.

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Álvaro Herrera http://www.2ndQuadrant.com/
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