Fix query cache hang when used by node.js.

node.js sends a query in following pattern:

Parse
Bind
Describe
Execute
Flush
Sync

Notice the "Flush" message. This is unnecessary message and Pgpool-II
did not prepare for it. Since Pgpool-I supposed that next message to
Execute is "Sync" in pool_fetch_from_memory_cache(), it actually read
the "Flush" message and forwarded to backend, then discarded
subsequent "Ready for query" message, which was actually a "Sync"
message. That results in no "ready for query" message from backend.

Fix is, do not have any assumption regarding messages after Execute,
instead returns to the message processing loop. This way, whatever
messages coming after Execute should be properly processed.

Following is the test data for pgproto.

'Q'	"DROP TABLE IF EXISTS pgproto_test1"
'Y'
'Q'	"CREATE TABLE pgproto_test1(i INT)"
'Y'
'Q'	"INSERT INTO pgproto_test1 VALUES(1)"
'Y'

'P'	"S2"	"SELECT 1 FROM pgproto_test1"	0
'B'	""	"S2"	0	0	0
'D'	'S'	"S2"
'E'	""	0
'H'
'C'	'S'	"S2"
'S'
'Y'

'P'	"S2"	"SELECT 1 FROM pgproto_test1"	0
'B'	""	"S2"	0	0	0
'D'	'S'	"S2"
'E'	""	0
'H'
'C'	'S'	"S2"
'S'
'Y'
'X'

Discussion: http://www.pgpool.net/pipermail/pgpool-general/2017-May/005569.html

diff --git a/src/query_cache/pool_memqcache.c b/src/query_cache/pool_memqcache.c
index eee34dafb0cd66d293ebaeb60c2291b554dc8daf..73b9751a4f45ff77937102d1af61eb7a4de02d9e 100644 (file)
--- a/src/query_cache/pool_memqcache.c
+++ b/src/query_cache/pool_memqcache.c
@@ -645,43 +645,9 @@ POOL_STATUS pool_fetch_from_memory_cache(POOL_CONNECTION *frontend,
        pfree(qcache);
 
        /*
-        * 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.
+        * Send a "READY FOR QUERY" if not in extended 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;
-               if (pool_read(frontend, &kind, 1))
-                       return POOL_END;
-
-               ereport(DEBUG2,
-                               (errmsg("memcache: fetching from memory cache: expecting sync: kind '%c'", kind)));
-               if (pool_read(frontend, &len, sizeof(len)))
-                       return POOL_END;
-
-               /* Forward "Sync" message to backend */
-               session_context = pool_get_session_context(true);
-               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));
-       }
-
-       /*
-        * send a "READY FOR QUERY"
-        */
-       if (MAJOR(backend) == PROTO_MAJOR_V3)
+       if (!pool_is_doing_extended_query_message() && MAJOR(backend) == PROTO_MAJOR_V3)
        {
                signed char state;
 
@@ -691,10 +657,7 @@ POOL_STATUS pool_fetch_from_memory_cache(POOL_CONNECTION *frontend,
                state = MASTER(backend)->tstate;
                send_message(frontend, 'Z', 5, (char *)&state);
        }
-       else
-       {
-               pool_write(frontend, "Z", 1);
-       }
+
        if (pool_flush(frontend))
        {
                return POOL_END;