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: 2019-08-31T08:04:01Z
Lists: pgsql-hackers 
On Thu, Aug 29, 2019 at 10:10 PM Peter Geoghegan <pg@bowt.ie> wrote:
> I see some Valgrind errors on v9, all of which look like the following
> two sample errors I go into below.

I've found a fix for these Valgrind issues. It's a matter of making
sure that _bt_truncate() sizes new pivot tuples properly, which is
quite subtle:

--- a/src/backend/access/nbtree/nbtutils.c
+++ b/src/backend/access/nbtree/nbtutils.c
@@ -2155,8 +2155,11 @@ _bt_truncate(Relation rel, IndexTuple lastleft,
IndexTuple firstright,
         {
             BTreeTupleClearBtIsPosting(pivot);
             BTreeTupleSetNAtts(pivot, keepnatts);
-            pivot->t_info &= ~INDEX_SIZE_MASK;
-            pivot->t_info |= BTreeTupleGetPostingOffset(firstright);
+            if (keepnatts == natts)
+            {
+                pivot->t_info &= ~INDEX_SIZE_MASK;
+                pivot->t_info |=
MAXALIGN(BTreeTupleGetPostingOffset(firstright));
+            }
         }

I'm varying how the new pivot tuple is sized here according to whether
or not index_truncate_tuple() just does a CopyIndexTuple(). This very
slightly changes the behavior of the nbtsplitloc.c stuff, but that's
not a concern for me.

I will post a patch with this and other tweaks next week.

--
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.