Fix initial sync of slot parent directory when restoring status

At the beginning of recovery, information from replication slots is
recovered from disk to memory.  In order to ensure the durability of the
information, the status file as well as its parent directory are
synced.  It happens that the sync on the parent directory was done
directly using the status file path, which is logically incorrect, and
the current code has been doing a sync on the same object twice in a
row.

Reported-by: Konstantin Knizhnik
Diagnosed-by: Konstantin Knizhnik
Author: Michael Paquier
Discussion: https://postgr.es/m/9eb1a6d5-b66f-2640-598d-c5ea46b8f68a@postgrespro.ru
Backpatch-through: 9.4-

diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index af47cdab0ebe08d5d56ef0924f85586a5bcf91e2..a538ae17541597b9c88b2fbc6833098568200680 100644 (file)
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1101,6 +1101,7 @@ RestoreSlotFromDisk(const char *name)
 {
    ReplicationSlotOnDisk cp;
    int         i;
+   char        slotdir[MAXPGPATH + 12];
    char        path[MAXPGPATH + 22];
    int         fd;
    bool        restored = false;
@@ -1110,13 +1111,14 @@ RestoreSlotFromDisk(const char *name)
    /* no need to lock here, no concurrent access allowed yet */
 
    /* delete temp file if it exists */
-   sprintf(path, "pg_replslot/%s/state.tmp", name);
+   sprintf(slotdir, "pg_replslot/%s", name);
+   sprintf(path, "%s/state.tmp", slotdir);
    if (unlink(path) < 0 && errno != ENOENT)
        ereport(PANIC,
                (errcode_for_file_access(),
                 errmsg("could not remove file \"%s\": %m", path)));
 
-   sprintf(path, "pg_replslot/%s/state", name);
+   sprintf(path, "%s/state", slotdir);
 
    elog(DEBUG1, "restoring replication slot from \"%s\"", path);
 
@@ -1149,7 +1151,7 @@ RestoreSlotFromDisk(const char *name)
 
    /* Also sync the parent directory */
    START_CRIT_SECTION();
-   fsync_fname(path, true);
+   fsync_fname(slotdir, true);
    END_CRIT_SECTION();
 
    /* read part of statefile that's guaranteed to be version independent */
@@ -1224,13 +1226,11 @@ RestoreSlotFromDisk(const char *name)
     */
    if (cp.slotdata.persistency != RS_PERSISTENT)
    {
-       sprintf(path, "pg_replslot/%s", name);
-
-       if (!rmtree(path, true))
+       if (!rmtree(slotdir, true))
        {
            ereport(WARNING,
                    (errcode_for_file_access(),
-                    errmsg("could not remove directory \"%s\"", path)));
+                    errmsg("could not remove directory \"%s\"", slotdir)));
        }
        fsync_fname("pg_replslot", true);
        return;