Feedback-ID: ia2694551:Fastmail
Date: Wed, 9 Aug 2023 11:11:55 +0200
From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: pgsql-hackers@lists.postgresql.org
Cc: Matthias van de Meent <boekewurm+postgres@gmail.com>,
	Tomas Vondra <tomas.vondra@postgresql.org>,
	Josef =?utf-8?B?xaBpbcOhbmVr?= <josef.simanek@gmail.com>
Subject: Re: pgsql: Ignore BRIN indexes when checking for HOT udpates
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On 2021-Nov-30, Tomas Vondra wrote:

> Ignore BRIN indexes when checking for HOT udpates

I was trying to use RelationGetIndexAttrBitmap for something and
realized that its header comment does not really explain things very
well.  That was already the case before this commit, but it (this
commit) did add new possible values without mentioning them.  I propose
the attached comment-only patch.

-- 
Álvaro Herrera               48°01'N 7°57'E  —  https://www.EnterpriseDB.com/
Al principio era UNIX, y UNIX habló y dijo: "Hello world\n".
No dijo "Hello New Jersey\n", ni "Hello USA\n".

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	filename="0001-Document-RelationGetIndexAttrBitmap-better.patch"

From db4c89d15d121bf0e15c4160cb2f0770bc98195a Mon Sep 17 00:00:00 2001
From: Alvaro Herrera <alvherre@alvh.no-ip.org>
Date: Wed, 12 Jul 2023 14:19:23 +0200
Subject: [PATCH] Document RelationGetIndexAttrBitmap better

Commit 19d8e2308bc5 changed the list of set-of-columns that can be
returned by RelationGetIndexAttrBitmap, but didn't update its
"documentation".  That was pretty hard to read already, so rewrite to
make it more comprehensible, adding the missing values while at it.

Backpatch to 16, like that commit.
---
 src/backend/utils/cache/relcache.c | 12 +++++++++---
 src/include/utils/relcache.h       |  3 +++
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/src/backend/utils/cache/relcache.c b/src/backend/utils/cache/relcache.c
index 8e28335915..8e08ca1c68 100644
--- a/src/backend/utils/cache/relcache.c
+++ b/src/backend/utils/cache/relcache.c
@@ -5150,9 +5150,15 @@ RelationGetIndexPredicate(Relation relation)
  * simple index keys, but attributes used in expressions and partial-index
  * predicates.)
  *
- * Depending on attrKind, a bitmap covering the attnums for all index columns,
- * for all potential foreign key columns, or for all columns in the configured
- * replica identity index is returned.
+ * Depending on attrKind, a bitmap covering attnums for certain columns is
+ * returned:
+ *	INDEX_ATTR_BITMAP_KEY			Columns in non-partial unique indexes not
+ *									in expressions (i.e., usable for FKs)
+ *	INDEX_ATTR_BITMAP_PRIMARY_KEY	Columns in the table's primary key
+ *	INDEX_ATTR_BITMAP_IDENTITY_KEY	Columns in the table's replica identity
+ *									index (empty if FULL)
+ *	INDEX_ATTR_BITMAP_HOT_BLOCKING	Columns that block updates from being HOT
+ *	INDEX_ATTR_BITMAP_SUMMARIZED	Columns included in summarizing indexes
  *
  * Attribute numbers are offset by FirstLowInvalidHeapAttributeNumber so that
  * we can include system attributes (e.g., OID) in the bitmap representation.
diff --git a/src/include/utils/relcache.h b/src/include/utils/relcache.h
index beeb28b83c..38524641f4 100644
--- a/src/include/utils/relcache.h
+++ b/src/include/utils/relcache.h
@@ -54,6 +54,9 @@ extern List *RelationGetIndexPredicate(Relation relation);
 extern Datum *RelationGetIndexRawAttOptions(Relation indexrel);
 extern bytea **RelationGetIndexAttOptions(Relation relation, bool copy);
 
+/*
+ * Which set of columns to return by RelationGetIndexAttrBitmap.
+ */
 typedef enum IndexAttrBitmapKind
 {
 	INDEX_ATTR_BITMAP_KEY,
-- 
2.39.2


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