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 17e00c4d5c68b0748e0c71eecd0c29f88abe654e..9c05dabaf7abf0472f5ce2e4f738509942d3519f 100644 (file)
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -1346,6 +1346,7 @@ RestoreSlotFromDisk(const char *name)
 {
    ReplicationSlotOnDisk cp;
    int         i;
+   char        slotdir[MAXPGPATH + 12];
    char        path[MAXPGPATH + 22];
    int         fd;
    bool        restored = false;
@@ -1355,13 +1356,14 @@ 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);
 
@@ -1396,7 +1398,7 @@ 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 */
@@ -1475,13 +1477,11 @@ 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;