[Nathan Bossart <nathandbossart@gmail.com>]

While examining pg_upgrade on a cluster with many tables (created with the
command in [0]), I noticed that a huge amount of pg_dump time goes towards
the binary_upgrade_set_pg_class_oids() function.  This function executes a
rather expensive query for a single row, and this function appears to be
called for most of the rows in pg_class.

The attached work-in-progress patch speeds up 'pg_dump --binary-upgrade'
for this case.  Instead of executing the query in every call to the
function, we can execute it once during the first call and store all the
required information in a sorted array that we can bsearch() in future
calls.  For the aformentioned test, pg_dump on my machine goes from ~2
minutes to ~18 seconds, which is much closer to the ~14 seconds it takes
without --binary-upgrade.

One downside of this approach is the memory usage.  This was more-or-less
the first approach that crossed my mind, so I wouldn't be surprised if
there's a better way.  I tried to keep the pg_dump output the same, but if
that isn't important, maybe we could dump all the pg_class OIDs at once
instead of calling binary_upgrade_set_pg_class_oids() for each one.

[0] https://postgr.es/m/3612876.1689443232%40sss.pgh.pa.us

-- 
Nathan Bossart
Amazon Web Services: https://aws.amazon.com

Attachments:

v1-0001-Improve-performance-of-pg_dump-binary-upgrade.patch (text/x-diff, 7.5K) download
From 27b4a3249dd97376f13a7c99505330ab7cd78e3f Mon Sep 17 00:00:00 2001
From: Nathan Bossart <nathan@postgresql.org>
Date: Wed, 17 Apr 2024 22:55:27 -0500
Subject: [PATCH v1 1/1] Improve performance of pg_dump --binary-upgrade.

---
 src/bin/pg_dump/pg_dump.c        | 113 +++++++++++++++++++------------
 src/tools/pgindent/typedefs.list |   1 +
 2 files changed, 70 insertions(+), 44 deletions(-)

diff --git a/src/bin/pg_dump/pg_dump.c b/src/bin/pg_dump/pg_dump.c
index c52e961b30..d93d974108 100644
--- a/src/bin/pg_dump/pg_dump.c
+++ b/src/bin/pg_dump/pg_dump.c
@@ -55,6 +55,7 @@
 #include "catalog/pg_trigger_d.h"
 #include "catalog/pg_type_d.h"
 #include "common/connect.h"
+#include "common/int.h"
 #include "common/relpath.h"
 #include "compress_io.h"
 #include "dumputils.h"
@@ -99,6 +100,17 @@ typedef enum OidOptions
 	zeroAsNone = 4,
 } OidOptions;
 
+typedef struct
+{
+	Oid			oid;
+	char		relkind;
+	RelFileNumber relfilenode;
+	Oid			reltoastrelid;
+	RelFileNumber toast_relfilenode;
+	Oid			indexrelid;
+	RelFileNumber toast_index_relfilenode;
+} BinaryUpgradeClassOids;
+
 /* global decls */
 static bool dosync = true;		/* Issue fsync() to make dump durable on disk. */
 
@@ -5392,19 +5404,56 @@ binary_upgrade_set_type_oids_by_rel(Archive *fout,
 												 pg_type_oid, false, false);
 }
 
+static int
+BinaryUpgradeClassOidsCmp(const void *p1, const void *p2)
+{
+	BinaryUpgradeClassOids v1 = *((const BinaryUpgradeClassOids *) p1);
+	BinaryUpgradeClassOids v2 = *((const BinaryUpgradeClassOids *) p2);
+
+	return pg_cmp_u32(v1.oid, v2.oid);
+}
+
 static void
 binary_upgrade_set_pg_class_oids(Archive *fout,
 								 PQExpBuffer upgrade_buffer, Oid pg_class_oid,
 								 bool is_index)
 {
-	PQExpBuffer upgrade_query = createPQExpBuffer();
-	PGresult   *upgrade_res;
-	RelFileNumber relfilenumber;
-	Oid			toast_oid;
-	RelFileNumber toast_relfilenumber;
-	char		relkind;
-	Oid			toast_index_oid;
-	RelFileNumber toast_index_relfilenumber;
+	static BinaryUpgradeClassOids *oids = NULL;
+	static int	oids_len = 0;
+	BinaryUpgradeClassOids key = {0, '?', 0, 0, 0, 0, 0};
+	BinaryUpgradeClassOids *entry;
+
+	if (oids == NULL)
+	{
+		PGresult   *res;
+
+		res = ExecuteSqlQuery(fout,
+							  "SELECT c.oid, c.relkind, c.relfilenode, c.reltoastrelid, ct.relfilenode AS toast_relfilenode, "
+							  "i.indexrelid, cti.relfilenode AS toast_index_relfilenode "
+							  "FROM pg_catalog.pg_class c LEFT JOIN "
+							  "pg_catalog.pg_index i ON (c.reltoastrelid = i.indrelid AND i.indisvalid) "
+							  "LEFT JOIN pg_catalog.pg_class ct ON (c.reltoastrelid = ct.oid) "
+							  "LEFT JOIN pg_catalog.pg_class AS cti ON (i.indexrelid = cti.oid) "
+							  "ORDER BY c.oid;",
+							  PGRES_TUPLES_OK);
+
+		oids_len = PQntuples(res);
+		oids = (BinaryUpgradeClassOids *)
+			pg_malloc(oids_len * sizeof(BinaryUpgradeClassOids));
+
+		for (int i = 0; i < oids_len; i++)
+		{
+			oids[i].oid = atooid(PQgetvalue(res, i, 0));
+			oids[i].relkind = *PQgetvalue(res, i, 1);
+			oids[i].relfilenode = atooid(PQgetvalue(res, i, 2));
+			oids[i].reltoastrelid = atooid(PQgetvalue(res, i, 3));
+			oids[i].toast_relfilenode = atooid(PQgetvalue(res, i, 4));
+			oids[i].indexrelid = atooid(PQgetvalue(res, i, 5));
+			oids[i].toast_index_relfilenode = atooid(PQgetvalue(res, i, 6));
+		}
+
+		PQclear(res);
+	}
 
 	/*
 	 * Preserve the OID and relfilenumber of the table, table's index, table's
@@ -5417,29 +5466,9 @@ binary_upgrade_set_pg_class_oids(Archive *fout,
 	 * by the new backend, so we can copy the files during binary upgrade
 	 * without worrying about this case.
 	 */
-	appendPQExpBuffer(upgrade_query,
-					  "SELECT c.relkind, c.relfilenode, c.reltoastrelid, ct.relfilenode AS toast_relfilenode, i.indexrelid, cti.relfilenode AS toast_index_relfilenode "
-					  "FROM pg_catalog.pg_class c LEFT JOIN "
-					  "pg_catalog.pg_index i ON (c.reltoastrelid = i.indrelid AND i.indisvalid) "
-					  "LEFT JOIN pg_catalog.pg_class ct ON (c.reltoastrelid = ct.oid) "
-					  "LEFT JOIN pg_catalog.pg_class AS cti ON (i.indexrelid = cti.oid) "
-					  "WHERE c.oid = '%u'::pg_catalog.oid;",
-					  pg_class_oid);
-
-	upgrade_res = ExecuteSqlQueryForSingleRow(fout, upgrade_query->data);
-
-	relkind = *PQgetvalue(upgrade_res, 0, PQfnumber(upgrade_res, "relkind"));
-
-	relfilenumber = atooid(PQgetvalue(upgrade_res, 0,
-									  PQfnumber(upgrade_res, "relfilenode")));
-	toast_oid = atooid(PQgetvalue(upgrade_res, 0,
-								  PQfnumber(upgrade_res, "reltoastrelid")));
-	toast_relfilenumber = atooid(PQgetvalue(upgrade_res, 0,
-											PQfnumber(upgrade_res, "toast_relfilenode")));
-	toast_index_oid = atooid(PQgetvalue(upgrade_res, 0,
-										PQfnumber(upgrade_res, "indexrelid")));
-	toast_index_relfilenumber = atooid(PQgetvalue(upgrade_res, 0,
-												  PQfnumber(upgrade_res, "toast_index_relfilenode")));
+	key.oid = pg_class_oid;
+	entry = bsearch(&key, oids, oids_len, sizeof(BinaryUpgradeClassOids),
+					BinaryUpgradeClassOidsCmp);
 
 	appendPQExpBufferStr(upgrade_buffer,
 						 "\n-- For binary upgrade, must preserve pg_class oids and relfilenodes\n");
@@ -5455,35 +5484,33 @@ binary_upgrade_set_pg_class_oids(Archive *fout,
 		 * partitioned tables have a relfilenumber, which should not be
 		 * preserved when upgrading.
 		 */
-		if (RelFileNumberIsValid(relfilenumber) && relkind != RELKIND_PARTITIONED_TABLE)
+		if (RelFileNumberIsValid(entry->relfilenode) && entry->relkind != RELKIND_PARTITIONED_TABLE)
 			appendPQExpBuffer(upgrade_buffer,
 							  "SELECT pg_catalog.binary_upgrade_set_next_heap_relfilenode('%u'::pg_catalog.oid);\n",
-							  relfilenumber);
+							  entry->relfilenode);
 
 		/*
 		 * In a pre-v12 database, partitioned tables might be marked as having
 		 * toast tables, but we should ignore them if so.
 		 */
-		if (OidIsValid(toast_oid) &&
-			relkind != RELKIND_PARTITIONED_TABLE)
+		if (OidIsValid(entry->reltoastrelid) &&
+			entry->relkind != RELKIND_PARTITIONED_TABLE)
 		{
 			appendPQExpBuffer(upgrade_buffer,
 							  "SELECT pg_catalog.binary_upgrade_set_next_toast_pg_class_oid('%u'::pg_catalog.oid);\n",
-							  toast_oid);
+							  entry->reltoastrelid);
 			appendPQExpBuffer(upgrade_buffer,
 							  "SELECT pg_catalog.binary_upgrade_set_next_toast_relfilenode('%u'::pg_catalog.oid);\n",
-							  toast_relfilenumber);
+							  entry->toast_relfilenode);
 
 			/* every toast table has an index */
 			appendPQExpBuffer(upgrade_buffer,
 							  "SELECT pg_catalog.binary_upgrade_set_next_index_pg_class_oid('%u'::pg_catalog.oid);\n",
-							  toast_index_oid);
+							  entry->indexrelid);
 			appendPQExpBuffer(upgrade_buffer,
 							  "SELECT pg_catalog.binary_upgrade_set_next_index_relfilenode('%u'::pg_catalog.oid);\n",
-							  toast_index_relfilenumber);
+							  entry->toast_index_relfilenode);
 		}
-
-		PQclear(upgrade_res);
 	}
 	else
 	{
@@ -5493,12 +5520,10 @@ binary_upgrade_set_pg_class_oids(Archive *fout,
 						  pg_class_oid);
 		appendPQExpBuffer(upgrade_buffer,
 						  "SELECT pg_catalog.binary_upgrade_set_next_index_relfilenode('%u'::pg_catalog.oid);\n",
-						  relfilenumber);
+						  entry->relfilenode);
 	}
 
 	appendPQExpBufferChar(upgrade_buffer, '\n');
-
-	destroyPQExpBuffer(upgrade_query);
 }
 
 /*
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index d551ada325..c8062a1a20 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -255,6 +255,7 @@ BernoulliSamplerData
 BgWorkerStartTime
 BgwHandleStatus
 BinaryArithmFunc
+BinaryUpgradeClassOids
 BindParamCbData
 BipartiteMatchState
 BitString
-- 
2.25.1