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: 2019-12-17T21:58:25Z
Lists: pgsql-hackers 
On Thu, Dec 12, 2019 at 06:21:20PM -0800, Peter Geoghegan wrote:
> On Tue, Dec 3, 2019 at 12:13 PM Peter Geoghegan <pg@bowt.ie> wrote:
> > The new criteria/heuristic for unique indexes is very simple: If a
> > unique index has an existing item that is a duplicate on the incoming
> > item at the point that we might have to split the page, then apply
> > deduplication. Otherwise (when the incoming item has no duplicates),
> > don't apply deduplication at all -- just accept that we'll have to
> > split the page. We already cache the bounds of our initial binary
> > search in insert state, so we can reuse that information within
> > _bt_findinsertloc() when considering deduplication in unique indexes.
> 
> Attached is v26, which adds this new criteria/heuristic for unique
> indexes. We now seem to consistently get good results with unique
> indexes.

In the past we tried to increase the number of cases where HOT updates
can happen but were unable to.  Would this help with non-HOT updates? 
Do we have any benchmarks where non-HOT updates cause slowdowns that we
can test on this?

-- 
  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.