Use a fd opened for read/write when syncing slots during startup, take 2.

Cribbing from dfbaed45975:
    Some operating systems, including the reporter's windows, return EBADFD
    or similar when fsync() is invoked on a O_RDONLY file descriptor.
    Unfortunately RestoreSlotFromDisk() does exactly that; which causes
    failures after restarts in at least some scenarios.

    If you hit the bug the error message will be something like
    ERROR: could not fsync file "pg_replslot/$name/state": Bad file descriptor

    Simply use O_RDWR instead of O_RDONLY when opening the relevant file
    descriptor to fix the bug.

Unfortunately this fix was undone in 82a5649fb9db. Re-apply, and add a
comment.

Bug: 16039
Reported-By: Hans Buschmann
Author: Andres Freund
Discussion: https://postgr.es/m/16039-196fc97cc05e141c@postgresql.org
Backpatch: 12-, as 82a5649fb9db

diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index b1bcd93345dacd459c73e548198d48f7e5c90e17..21ae8531b3ccb4974cde2c09580e519c63a289af 100644 (file)
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1386,7 +1386,8 @@ RestoreSlotFromDisk(const char *name)
 
        elog(DEBUG1, "restoring replication slot from \"%s\"", path);
 
-       fd = OpenTransientFile(path, O_RDONLY | PG_BINARY);
+       /* on some operating systems fsyncing a file requires O_RDWR */
+       fd = OpenTransientFile(path, O_RDWR | PG_BINARY);
 
        /*
         * We do not need to handle this as we are rename()ing the directory into