Fix handling of pg_stat_statements.stat temporary file

Write the file to a temporary name and then rename() it into the
permanent name, to ensure it can't end up half-written and corrupt
in case of a crash during shutdown.

Unlink the file after it has been read so it's removed from the data
directory and not included in base backups going to replication slaves.

diff --git a/contrib/pg_stat_statements/pg_stat_statements.c b/contrib/pg_stat_statements/pg_stat_statements.c
index 8347c8e9887a8baea8113d6697fa961a471ed960..06869fa344e8a5b23c613574f26787dd2e424fb8 100644 (file)
--- a/contrib/pg_stat_statements/pg_stat_statements.c
+++ b/contrib/pg_stat_statements/pg_stat_statements.c
@@ -511,6 +511,13 @@ pgss_shmem_startup(void)
 
    pfree(buffer);
    FreeFile(file);
+
+   /*
+    * Remove the file so it's not included in backups/replication
+    * slaves, etc. A new file will be written on next shutdown.
+    */
+   unlink(PGSS_DUMP_FILE);
+
    return;
 
 error:
@@ -552,7 +559,7 @@ pgss_shmem_shutdown(int code, Datum arg)
    if (!pgss_save)
        return;
 
-   file = AllocateFile(PGSS_DUMP_FILE, PG_BINARY_W);
+   file = AllocateFile(PGSS_DUMP_FILE ".tmp", PG_BINARY_W);
    if (file == NULL)
        goto error;
 
@@ -578,16 +585,25 @@ pgss_shmem_shutdown(int code, Datum arg)
        goto error;
    }
 
+   /*
+    * Rename file into place, so we atomically replace the old one.
+    */
+   if (rename(PGSS_DUMP_FILE ".tmp", PGSS_DUMP_FILE) != 0)
+       ereport(LOG,
+               (errcode_for_file_access(),
+                errmsg("could not rename pg_stat_statement file \"%s\": %m",
+                       PGSS_DUMP_FILE ".tmp")));
+
    return;
 
 error:
    ereport(LOG,
            (errcode_for_file_access(),
             errmsg("could not write pg_stat_statement file \"%s\": %m",
-                   PGSS_DUMP_FILE)));
+                   PGSS_DUMP_FILE  ".tmp")));
    if (file)
        FreeFile(file);
-   unlink(PGSS_DUMP_FILE);
+   unlink(PGSS_DUMP_FILE ".tmp");
 }
 
 /*