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: 2019-11-19T01:26:37Z
Lists: pgsql-hackers

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On Fri, Nov 15, 2019 at 5:02 PM Peter Geoghegan <pg@bowt.ie> wrote:
> What I saw suggests that we will need to remove the new "postingoff"
> field from xl_btree_insert. (We can create a new XLog record for leaf
> page inserts that also need to split a posting list, without changing
> much else.)

Attached is v24. This revision doesn't fix the problem with
xl_btree_insert record bloat, but it does fix the bitrot against the
master branch that was caused by commit 50d22de9. (This patch has had
a surprisingly large number of conflicts against the master branch
recently.)

Other changes:

* The pageinspect patch has been cleaned up. I now propose that it be
committed alongside the main patch.

The big change here is that posting lists are represented as an array
of TIDs within bt_page_items(), much like gin_leafpage_items(). Also
added documentation that goes into the ways in which ctid can be used
to encode information (arguably some of this should have been included
with the Postgres 12 B-Tree work).

* Basic tests that cover deduplication within unique indexes. We ought
to have code coverage of the case where _bt_check_unique() has to step
right (actually, we don't have that on the master branch either).

-- 
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.