Preserve index data in pg_statistic across REINDEX CONCURRENTLY

Statistics associated to an index got lost after running REINDEX
CONCURRENTLY, while the non-concurrent case preserves these correctly.
The concurrent and non-concurrent operations need to be consistent for
the end-user, and missing statistics would force to wait for a new
analyze to happen, which could take some time depending on the activity
of the existing autovacuum workers.  This issue is fixed by copying any
existing entries in pg_statistic associated to the old index to the new
one.  Note that this copy is already done with the data of the index in
the stats collector.

Reported-by: Fabrízio de Royes Mello
Author: Michael Paquier, Fabrízio de Royes Mello
Reviewed-by: Justin Pryzby
Discussion: https://postgr.es/m/CAFcNs+qpFPmiHd1oTXvcPdvAHicJDA9qBUSujgAhUMJyUMb+SA@mail.gmail.com
Backpatch-through: 12

2 files changed, 44 insertions, 0 deletions

diff --git a/src/backend/catalog/heap.c b/src/backend/catalog/heap.c
index 67144aa3c94..9ccf378d45b 100644
--- a/src/backend/catalog/heap.c
+++ b/src/backend/catalog/heap.c
@@ -3142,6 +3142,47 @@ cookConstraint(ParseState *pstate,
 	return expr;
 }
 
+/*
+ * CopyStatistics --- copy entries in pg_statistic from one rel to another
+ */
+void
+CopyStatistics(Oid fromrelid, Oid torelid)
+{
+	HeapTuple	tup;
+	SysScanDesc scan;
+	ScanKeyData key[1];
+	Relation	statrel;
+
+	statrel = table_open(StatisticRelationId, RowExclusiveLock);
+
+	/* Now search for stat records */
+	ScanKeyInit(&key[0],
+				Anum_pg_statistic_starelid,
+				BTEqualStrategyNumber, F_OIDEQ,
+				ObjectIdGetDatum(fromrelid));
+
+	scan = systable_beginscan(statrel, StatisticRelidAttnumInhIndexId,
+							  true, NULL, 1, key);
+
+	while (HeapTupleIsValid((tup = systable_getnext(scan))))
+	{
+		Form_pg_statistic statform;
+
+		/* make a modifiable copy */
+		tup = heap_copytuple(tup);
+		statform = (Form_pg_statistic) GETSTRUCT(tup);
+
+		/* update the copy of the tuple and insert it */
+		statform->starelid = torelid;
+		CatalogTupleInsert(statrel, tup);
+
+		heap_freetuple(tup);
+	}
+
+	systable_endscan(scan);
+
+	table_close(statrel, RowExclusiveLock);
+}
 
 /*
  * RemoveStatistics --- remove entries in pg_statistic for a rel or column
diff --git a/src/backend/catalog/index.c b/src/backend/catalog/index.c
index 0974f3e23a2..a18cc7cad30 100644
--- a/src/backend/catalog/index.c
+++ b/src/backend/catalog/index.c
@@ -1711,6 +1711,9 @@ index_concurrently_swap(Oid newIndexId, Oid oldIndexId, const char *oldName)
 		}
 	}
 
+	/* Copy data of pg_statistic from the old index to the new one */
+	CopyStatistics(oldIndexId, newIndexId);
+
 	/* Close relations */
 	table_close(pg_class, RowExclusiveLock);
 	table_close(pg_index, RowExclusiveLock);