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-rw-r--r--src/backend/storage/smgr/md.c8
1 files changed, 7 insertions, 1 deletions
diff --git a/src/backend/storage/smgr/md.c b/src/backend/storage/smgr/md.c
index 5458cbdda42..c0e41c7053b 100644
--- a/src/backend/storage/smgr/md.c
+++ b/src/backend/storage/smgr/md.c
@@ -33,7 +33,13 @@
/* interval for calling AbsorbFsyncRequests in mdsync */
#define FSYNCS_PER_ABSORB 10
-/* special values for the segno arg to RememberFsyncRequest */
+/*
+ * Special values for the segno arg to RememberFsyncRequest.
+ *
+ * Note that CompactBgwriterRequestQueue assumes that it's OK to remove an
+ * fsync request from the queue if an identical, subsequent request is found.
+ * See comments there before making changes here.
+ */
#define FORGET_RELATION_FSYNC (InvalidBlockNumber)
#define FORGET_DATABASE_FSYNC (InvalidBlockNumber-1)
#define UNLINK_RELATION_REQUEST (InvalidBlockNumber-2)