>From be59001586a9baa731876744fa84cf7987b59fe3 Mon Sep 17 00:00:00 2001
From: Andres Freund <andres@anarazel.de>
Date: Mon, 19 Aug 2013 13:24:30 +0200
Subject: [PATCH 3/8] wal_decoding: Add information about a tables primary key
 to struct RelationData

'rd_primary' now contains the Oid of an index over uniquely identifying
columns. Several types of indexes are interesting and are collected in that
order:
* Primary Key
* oid index
* the first (OID order) unique, immediate, non-partial and
  non-expression index over one or more NOT NULL'ed columns

To gather rd_primary value RelationGetIndexList() needs to have been called.

This is helpful because for logical replication we frequently - on the sending
and receiving side - need to lookup that index and RelationGetIndexList already
gathers all the necessary information.

This could be used to replace tablecmd.c's transformFkeyGetPrimaryKey, but
would change the meaning of that, so it seems to require additional discussion.
---
 src/backend/utils/cache/relcache.c | 52 +++++++++++++++++++++++++++++++++++---
 src/include/utils/rel.h            | 12 +++++++++
 2 files changed, 61 insertions(+), 3 deletions(-)

diff --git a/src/backend/utils/cache/relcache.c b/src/backend/utils/cache/relcache.c
index b4cc6ad..44dd0d2 100644
--- a/src/backend/utils/cache/relcache.c
+++ b/src/backend/utils/cache/relcache.c
@@ -3462,7 +3462,9 @@ RelationGetIndexList(Relation relation)
 	ScanKeyData skey;
 	HeapTuple	htup;
 	List	   *result;
-	Oid			oidIndex;
+	Oid			oidIndex = InvalidOid;
+	Oid			pkeyIndex = InvalidOid;
+	Oid			candidateIndex = InvalidOid;
 	MemoryContext oldcxt;
 
 	/* Quick exit if we already computed the list. */
@@ -3519,17 +3521,61 @@ RelationGetIndexList(Relation relation)
 		Assert(!isnull);
 		indclass = (oidvector *) DatumGetPointer(indclassDatum);
 
+		if (!IndexIsValid(index))
+			continue;
+
 		/* Check to see if it is a unique, non-partial btree index on OID */
-		if (IndexIsValid(index) &&
-			index->indnatts == 1 &&
+		if (index->indnatts == 1 &&
 			index->indisunique && index->indimmediate &&
 			index->indkey.values[0] == ObjectIdAttributeNumber &&
 			indclass->values[0] == OID_BTREE_OPS_OID &&
 			heap_attisnull(htup, Anum_pg_index_indpred))
 			oidIndex = index->indexrelid;
+
+		if (index->indisunique &&
+			index->indimmediate &&
+			heap_attisnull(htup, Anum_pg_index_indpred))
+		{
+			/* always prefer primary keys */
+			if (index->indisprimary)
+				pkeyIndex = index->indexrelid;
+			else if (!OidIsValid(pkeyIndex)
+					&& !OidIsValid(oidIndex)
+					&& !OidIsValid(candidateIndex))
+			{
+				int key;
+				bool found = true;
+				for (key = 0; key < index->indnatts; key++)
+				{
+					int16 attno = index->indkey.values[key];
+					Form_pg_attribute attr;
+					/* internal column, like oid */
+					if (attno <= 0)
+						continue;
+
+					attr = relation->rd_att->attrs[attno - 1];
+					if (!attr->attnotnull)
+					{
+						found = false;
+						break;
+					}
+				}
+				if (found)
+					candidateIndex = index->indexrelid;
+			}
+		}
 	}
 
 	systable_endscan(indscan);
+
+	if (OidIsValid(pkeyIndex))
+		relation->rd_primary = pkeyIndex;
+	/* prefer oid indexes over normal candidate ones */
+	else if (OidIsValid(oidIndex))
+		relation->rd_primary = oidIndex;
+	else if (OidIsValid(candidateIndex))
+		relation->rd_primary = candidateIndex;
+
 	heap_close(indrel, AccessShareLock);
 
 	/* Now save a copy of the completed list in the relcache entry. */
diff --git a/src/include/utils/rel.h b/src/include/utils/rel.h
index 589c9a8..0281b4b 100644
--- a/src/include/utils/rel.h
+++ b/src/include/utils/rel.h
@@ -111,6 +111,18 @@ typedef struct RelationData
 	TriggerDesc *trigdesc;		/* Trigger info, or NULL if rel has none */
 
 	/*
+	 * The 'best' primary or candidate key that has been found, only set
+	 * correctly if RelationGetIndexList has been called/rd_indexvalid > 0.
+	 *
+	 * Indexes are chosen in the following order:
+	 * * Primary Key
+	 * * oid index
+	 * * the first (OID order) unique, immediate, non-partial and
+	 *   non-expression index over one or more NOT NULL'ed columns
+	 */
+	Oid rd_primary;
+
+	/*
 	 * rd_options is set whenever rd_rel is loaded into the relcache entry.
 	 * Note that you can NOT look into rd_rel for this data.  NULL means "use
 	 * defaults".
-- 
1.8.4.21.g992c386.dirty