Fix memory leak and inefficiency in CREATE DATABASE ... STRATEGY WAL_LOG

RelationCopyStorageUsingBuffer() did not free the strategies used to access
the source / target relation. They memory was released at the end of the
transaction, but when using a template database with a lot of relations, the
temporary leak can become big prohibitively big.

RelationCopyStorageUsingBuffer() acquired the buffer for the target relation
with RBM_NORMAL, therefore requiring a read of a block guaranteed to be
zero. Use RBM_ZERO_AND_LOCK instead.

Reviewed-by: Robert Haas <robertmhaas@gmail.com>
Discussion: https://postgr.es/m/20230321070113.o2vqqxogjykwgfrr@awork3.anarazel.de
Backpatch: 15-, where STRATEGY WAL_LOG was introduced

diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index 0a05577b68df21349fe1dc2a1018b2985e66dbb8..95212a39416eece3a448f12cb8f82dc53a9f78e7 100644 (file)
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -3833,11 +3833,9 @@ RelationCopyStorageUsingBuffer(RelFileLocator srclocator,
        LockBuffer(srcBuf, BUFFER_LOCK_SHARE);
        srcPage = BufferGetPage(srcBuf);
 
-       /* Use P_NEW to extend the destination relation. */
        dstBuf = ReadBufferWithoutRelcache(dstlocator, forkNum, blkno,
-                                          RBM_NORMAL, bstrategy_dst,
+                                          RBM_ZERO_AND_LOCK, bstrategy_dst,
                                           permanent);
-       LockBuffer(dstBuf, BUFFER_LOCK_EXCLUSIVE);
        dstPage = BufferGetPage(dstBuf);
 
        START_CRIT_SECTION();
@@ -3855,6 +3853,9 @@ RelationCopyStorageUsingBuffer(RelFileLocator srclocator,
        UnlockReleaseBuffer(dstBuf);
        UnlockReleaseBuffer(srcBuf);
    }
+
+   FreeAccessStrategy(bstrategy_src);
+   FreeAccessStrategy(bstrategy_dst);
 }
 
 /* ---------------------------------------------------------------------