Use CREATE DATABASE ... STRATEGY = FILE_COPY in pg_upgrade.

While this strategy is ordinarily quite costly because it requires
performing two checkpoints, testing shows that it tends to be a
faster choice than WAL_LOG during pg_upgrade, presumably because
fsync is turned off.  Furthermore, we can skip the checkpoints
altogether because the problems they are intended to prevent don't
apply to pg_upgrade.  Instead, we just need to CHECKPOINT once in
the new cluster after making any changes to template0 and before
restoring the rest of the databases.  This ensures that said
template0 changes are written out to disk prior to creating the
databases via FILE_COPY.

Co-authored-by: Matthias van de Meent
Reviewed-by: Ranier Vilela, Dilip Kumar, Robert Haas, Michael Paquier
Discussion: https://postgr.es/m/Zl9ta3FtgdjizkJ5%40nathan

1 files changed, 15 insertions, 3 deletions

diff --git a/src/backend/commands/dbcommands.c b/src/backend/commands/dbcommands.c
index be629ea92cf..7026352bc99 100644
--- a/src/backend/commands/dbcommands.c
+++ b/src/backend/commands/dbcommands.c
@@ -563,9 +563,14 @@ CreateDatabaseUsingFileCopy(Oid src_dboid, Oid dst_dboid, Oid src_tsid,
 	 * happened while we're copying files, a file might be deleted just when
 	 * we're about to copy it, causing the lstat() call in copydir() to fail
 	 * with ENOENT.
+	 *
+	 * In binary upgrade mode, we can skip this checkpoint because pg_upgrade
+	 * is careful to ensure that template0 is fully written to disk prior to
+	 * any CREATE DATABASE commands.
 	 */
-	RequestCheckpoint(CHECKPOINT_IMMEDIATE | CHECKPOINT_FORCE |
-					  CHECKPOINT_WAIT | CHECKPOINT_FLUSH_ALL);
+	if (!IsBinaryUpgrade)
+		RequestCheckpoint(CHECKPOINT_IMMEDIATE | CHECKPOINT_FORCE |
+						  CHECKPOINT_WAIT | CHECKPOINT_FLUSH_ALL);
 
 	/*
 	 * Iterate through all tablespaces of the template database, and copy each
@@ -657,10 +662,17 @@ CreateDatabaseUsingFileCopy(Oid src_dboid, Oid dst_dboid, Oid src_tsid,
 	 * seem to be much we can do about that except document it as a
 	 * limitation.
 	 *
+	 * In binary upgrade mode, we can skip this checkpoint because neither of
+	 * these problems applies: we don't ever replay the WAL generated during
+	 * pg_upgrade, and we don't support taking base backups during pg_upgrade
+	 * (not to mention that we don't concurrently modify template0, either).
+	 *
 	 * See CreateDatabaseUsingWalLog() for a less cheesy CREATE DATABASE
 	 * strategy that avoids these problems.
 	 */
-	RequestCheckpoint(CHECKPOINT_IMMEDIATE | CHECKPOINT_FORCE | CHECKPOINT_WAIT);
+	if (!IsBinaryUpgrade)
+		RequestCheckpoint(CHECKPOINT_IMMEDIATE | CHECKPOINT_FORCE |
+						  CHECKPOINT_WAIT);
 }
 
 /*