Horton

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

Bruce Momjian <bruce@momjian.us>

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From: Bruce Momjian <bruce@momjian.us>
To: Peter Geoghegan <pg@bowt.ie>
Cc: Anastasia Lubennikova <a.lubennikova@postgrespro.ru>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2019-12-18T01:17:58Z
Lists: pgsql-hackers 
On Tue, Dec 17, 2019 at 03:30:33PM -0800, Peter Geoghegan wrote:
> With many real world unique indexes, the true reason behind most or
> all B-Tree page splits is "version churn". I view these page splits as
> a permanent solution to a temporary problem -- we *permanently*
> degrade the index structure in order to deal with a *temporary* burst
> in versions that need to be stored. That's really bad.

Yes, I was thinking why do we need to optimize duplicates in a unique
index but then remembered is a version problem.

-- 
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

+ As you are, so once was I.  As I am, so you will be. +
+                      Ancient Roman grave inscription +

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.