#490 message missing in handle_response

peace zone — Fri, 26 Sep 2014 03:04:37 -0000

Thanks for your explanation, I will do as you say

#490 message missing in handle_response

peace zone — Fri, 26 Sep 2014 02:29:56 -0000

Thanks for your response!
1. I found this condition during doing the make check.
2. Do we have a plan to adding this feature?

message missing in handle_response

peace zone — Mon, 22 Sep 2014 09:41:32 -0000

I execute a user define function and get two different results. Both the two results appear randomly, the result2 is expected.

Results
results1:
postgres=# select trap_foreign_key(2);
NOTICE: caught foreign_key_violation
ERROR: failed to send COMMIT command to node

results2:
postgres=# select trap_foreign_key(2);
NOTICE: caught foreign_key_violation
trap_foreign_key
------------------
0
(1 row)

Object definition
CREATE TABLE master(f1 int primary key);
CREATE TABLE slave(f1 int references master deferrable);

CREATE FUNCTION trap_foreign_key(int) RETURNS INT AS $$
BEGIN
begin -- start transaction
insert into slave values($1);
exception
when foreign_key_violation then
raise notice 'caught foreign_key_violation';
return 0;
end;
return 1;
end$$ language plpgsql;

select trap_foreign_key(2); – detects FK violation

Debug output

I add a elog in handle_reponse() of coordinator:

msg_type = get_message(conn, &msg_len, &msg);
elog(WARNING, "Received message type: %c", msg_type);

The debug output is in the attachment.
As the debug output shows, the result1 misses the N, Z messages from datanode.

Reason

The reason is when the coordinator in justifing message buffer,
the datanode has not yet send the messages.The coordinator thinks
there is no message now, and return, the later messages from datanode is missed.

The coordinator code:
if (!HAS_MESSAGE_BUFFERED(conn))
return RESPONSE_EOF;

The N,Z messages comes later than the check above.

Recent changes to 490: message missing in handle_response

#490 message missing in handle_response

#490 message missing in handle_response

message missing in handle_response