Horton

Re: [HACKERS] [WIP] Effective storage of duplicates in B-tree index.

Peter Geoghegan <pg@bowt.ie>

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From: Peter Geoghegan <pg@bowt.ie>
To: Anastasia Lubennikova <a.lubennikova@postgrespro.ru>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2019-09-18T18:01:19Z
Lists: pgsql-hackers 
On Wed, Sep 18, 2019 at 10:43 AM Peter Geoghegan <pg@bowt.ie> wrote:
> This also suggests that making _bt_dedup_one_page() do raw page adds
> and page deletes to the page in shared_buffers (i.e. don't use a temp
> buffer page) could pay off. As I went into at the start of this
> e-mail, unnecessarily doing expensive things like copying large
> posting lists around is a real concern. Even if it isn't truly useful
> for _bt_dedup_one_page() to operate in a very incremental fashion,
> incrementalism is probably still a good thing to aim for -- it seems
> to make deduplication faster in all cases.

I think that I forgot to mention that I am concerned that the
kill_prior_tuple/LP_DEAD optimization could be applied less often
because _bt_dedup_one_page() operates too aggressively. That is a big
part of my general concern.

Maybe I'm wrong about this -- who knows? I definitely think that
LP_DEAD setting by _bt_check_unique() is generally a lot more
important than LP_DEAD setting by the kill_prior_tuple optimization,
and the patch won't affect unique indexes. Only very serious
benchmarking can give us a clear answer, though.

-- 
Peter Geoghegan

Commits

  1. Teach pageinspect about nbtree deduplication.

  2. Doc: Fix deduplicate_items index term.

  3. Revise BTP_HAS_GARBAGE nbtree VACUUM comments.

  4. Remove unneeded "pin scan" nbtree VACUUM code.

  5. Cleanup code in reloptions.h regarding reloption handling

  6. Catch invalid typlens in a couple of places

  7. Compute XID horizon for page level index vacuum on primary.

  8. Make heap TID a tiebreaker nbtree index column.

  9. Avoid pin scan for replay of XLOG_BTREE_VACUUM in all cases

  10. Revert buggy optimization of index scans

  11. Restructure index access method API to hide most of it at the C level.

  12. Reduce pinning and buffer content locking for btree scans.

  13. Avoid scanning nulls at the beginning of a btree index scan.