Don't ignore sync message from frontend when query cache is enabled.

While returning cached query result, sync message sent from frontend
is discarded. This is harmless because "ready for query" messages is
sent to frontend afterward. Problem is, AccessShareLock held by
previous parse message processing is not released until sync message
is received by the backend. Fix is, forwarding the sync message to
backend and discarding "ready for query" message returned from
backend.

Per [pgpool-hackers: 1787].

diff --git a/pool_memqcache.c b/pool_memqcache.c
index a39e605dd5f7dbff99e415efa8eb75456a90e7e6..67b551eb76029b2501aeed8c180522e9ef711504 100644 (file)
--- a/pool_memqcache.c
+++ b/pool_memqcache.c
@@ -3,7 +3,7 @@
  * pgpool: a language independent connection pool server for PostgreSQL
  * written by Tatsuo Ishii
  *
- * Copyright (c) 2003-2014     PgPool Global Development Group
+ * Copyright (c) 2003-2016     PgPool Global Development Group
  *
  * Permission to use, copy, modify, and distribute this software and
  * its documentation for any purpose and without fee is hereby
@@ -579,14 +579,17 @@ POOL_STATUS pool_fetch_from_memory_cache(POOL_CONNECTION *frontend,
                free(qcache);
 
                /*
-                * If we are doing extended query, wait and discard Sync
-                * message from frontend. This is neccessary to prevent
-                * receiving Sync message after Sending Ready for query.
+                * If we are doing extended query, forward sync message from frontend to
+                * backend. This is necessary to prevent receiving Sync message after
+                * Sending Ready for query.
                 */
                if (pool_is_doing_extended_query_message())
                {
                        char kind;
                        int32 len;
+                       POOL_SESSION_CONTEXT *session_context;
+                       POOL_CONNECTION *target_backend;
+                       char buf[5];
 
                        if (pool_flush(frontend))
                                return POOL_END;
@@ -595,6 +598,16 @@ POOL_STATUS pool_fetch_from_memory_cache(POOL_CONNECTION *frontend,
                        pool_debug("pool_fetch_from_memory_cache: expecting sync: %c", kind);
                        if (pool_read(frontend, &len, sizeof(len)))
                                return POOL_END;
+
+                       /* Forward "Sync" message to backend */
+                       session_context = pool_get_session_context();
+                       target_backend = CONNECTION(backend, session_context->load_balance_node_id);
+                       pool_write(target_backend, &kind, 1);
+                       pool_write_and_flush(target_backend, &len, sizeof(len));
+
+                       /* Read and discard "Ready for query" message from backend */
+                       pool_read(target_backend, &kind, 1);
+                       pool_read(target_backend, buf, sizeof(buf));
                }
 
                /*