[pgpool-hackers: 4402] [pgpool-hackers] ERROR: unable to read message kind from backend

[Sadhuprasad Patro]

Hi Everyone,

I am running a Java customer application with PgPool LB feature with 2 DB nodes.
After some analysis, I figured out something as below:

In pool_pending_message_query_context_dest_set(), it sets
where_to_send field in query context, which tells to which node the
msg was sent.

/* Save where_to_send map */
memcpy(s->where_to_send_save, query_context->where_to_send,
sizeof(s->where_to_send_save));
s->need_to_restore_where_to_send = true;

 /* Rewrite where_to_send map */
memset(query_context->where_to_send, 0, sizeof(query_context->where_to_send));

for (i = 0; i < MAX_NUM_BACKENDS; i++)
{
      if (message->node_ids[i])
           query_context->where_to_send[i] = 1;
}

Here where_to_send field has been stored in session_context and memset
to 0 in query_context. Then we are setting it back only w.r.t nodeid
for which the msg has been sent.

At the end of the function, where_to_send field will be set to 1 only
for Node0, but for all other nodes, it will be 0.

LOG:  Message is SHOW TRANSACTION ISOLATION LEVEL
LOG:  pool_pending_message_query_context_dest_set:1251: Where to send
for Node0 is 1 & Where to send for Node1 is 0

Next it is going to “read_kind_from_one_backend()“, with MAIN_NODE_ID
as 1, for which where_to_send is already set to 0 as explained above.
Here we are considering the backend node 1 is not valid and raising
the error as:
ERROR: unable to read message kind from backend
Detail: 1 th backend is not valid

I am focusing further if the MAIN_NODE_ID is set wrong somehow. But
any help or suggestions ? Please let me know..

Thanks & Regards
SadhuPrasad