Don't forget about failed fsync() requests.

If fsync() fails, md.c must keep the request in its bitmap, so that
future attempts will try again.

Back-patch to all supported releases.

Author: Thomas Munro
Reviewed-by: Amit Kapila
Reported-by: Andrew Gierth
Discussion: https://postgr.es/m/87y3i1ia4w.fsf%40news-spur.riddles.org.uk

diff --git a/src/backend/storage/smgr/md.c b/src/backend/storage/smgr/md.c
index 86013a5c8b2f093724d40d05c82d6d315bf04fde..04c1069a60b994f1851210c975cc3bb731648a36 100644 (file)
--- a/src/backend/storage/smgr/md.c
+++ b/src/backend/storage/smgr/md.c
@@ -1123,10 +1123,8 @@ mdsync(void)
         * The bitmap manipulations are slightly tricky, because we can call
         * AbsorbFsyncRequests() inside the loop and that could result in
         * bms_add_member() modifying and even re-palloc'ing the bitmapsets.
-        * This is okay because we unlink each bitmapset from the hashtable
-        * entry before scanning it.  That means that any incoming fsync
-        * requests will be processed now if they reach the table before we
-        * begin to scan their fork.
+        * So we detach it, but if we fail we'll merge it with any new
+        * requests that have arrived in the meantime.
         */
        for (forknum = 0; forknum <= MAX_FORKNUM; forknum++)
        {
@@ -1136,7 +1134,8 @@ mdsync(void)
            entry->requests[forknum] = NULL;
            entry->canceled[forknum] = false;
 
-           while ((segno = bms_first_member(requests)) >= 0)
+           segno = -1;
+           while ((segno = bms_next_member(requests, segno)) >= 0)
            {
                int         failures;
 
@@ -1217,6 +1216,7 @@ mdsync(void)
                            longest = elapsed;
                        total_elapsed += elapsed;
                        processed++;
+                       requests = bms_del_member(requests, segno);
                        if (log_checkpoints)
                            elog(DEBUG1, "checkpoint sync: number=%d file=%s time=%.3f msec",
                                 processed,
@@ -1245,10 +1245,23 @@ mdsync(void)
                     */
                    if (!FILE_POSSIBLY_DELETED(errno) ||
                        failures > 0)
+                   {
+                       Bitmapset  *new_requests;
+
+                       /*
+                        * We need to merge these unsatisfied requests with
+                        * any others that have arrived since we started.
+                        */
+                       new_requests = entry->requests[forknum];
+                       entry->requests[forknum] =
+                           bms_join(new_requests, requests);
+
+                       errno = save_errno;
                        ereport(ERROR,
                                (errcode_for_file_access(),
                                 errmsg("could not fsync file \"%s\": %m",
                                        path)));
+                   }
                    else
                        ereport(DEBUG1,
                                (errcode_for_file_access(),