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Revert changes in HOT handling of BRIN indexes

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This reverts commits 5753d4ee32 and fe60b67250 that modified HOT to
ignore BRIN indexes. The commit message for 5753d4ee32 claims that:

    When determining whether an index update may be skipped by using
    HOT, we can ignore attributes indexed only by BRIN indexes. There
    are no index pointers to individual tuples in BRIN, and the page
    range summary will be updated anyway as it relies on visibility
    info.

This is partially incorrect - it's true BRIN indexes don't point to
individual tuples, so HOT chains are not an issue, but the visibitlity
info is not sufficient to keep the index up to date. This can easily
result in corrupted indexes, as demonstrated in the hackers thread.

This does not mean relaxing the HOT restrictions for BRIN is a lost
cause, but it needs to handle the two aspects (allowing HOT chains and
updating the page range summaries) as separate. But that requires a
major changes, and it's too late for that in the current dev cycle.

Reported-by: Tomas Vondra
Discussion: https://postgr.es/m/05ebcb44-f383-86e3-4f31-0a97a55634cf@enterprisedb.com
This commit is contained in:
Tomas Vondra
2022-06-16 15:02:48 +02:00
parent 664da2a389
commit e3fcca0d0d
17 changed files with 27 additions and 502 deletions
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11
doc/src/sgml/indexam.sgml
View File

@ -126,8 +126,6 @@ typedef struct IndexAmRoutine
bool amcaninclude;
/* does AM use maintenance_work_mem? */
bool amusemaintenanceworkmem;
/* does AM block HOT update? */
bool amhotblocking;
/* OR of parallel vacuum flags */
uint8 amparallelvacuumoptions;
/* type of data stored in index, or InvalidOid if variable */
@ -248,15 +246,6 @@ typedef struct IndexAmRoutine
null, independently of <structfield>amoptionalkey</structfield>.
</para>
<para>
The <structfield>amhotblocking</structfield> flag indicates whether the
access method blocks <acronym>HOT</acronym> when an indexed attribute is
updated. Access methods without pointers to individual tuples (like
<acronym>BRIN</acronym>) may allow <acronym>HOT</acronym> even in this
case. This does not apply to attributes referenced in index predicates;
an update of such attribute always disables <acronym>HOT</acronym>.
</para>
</sect1>
<sect1 id="index-functions">