[pgpool-hackers: 4404] Re: [pgpool-hackers] ERROR: unable to read message kind from backend

[Sadhuprasad Patro]

Hi Tatsuo Ishii,

 Issue is happening in PgPool 4.4.2 version.
And this issue is happening with EDB PgPool actually. Customer
testcase has some EDB specific msg. But the suspected code is same as
the Community PgPool code.

Some guidance on how & what to check further will also may help..

Thanks & Regards
SadhuPrasad

On Fri, Sep 29, 2023 at 12:21 PM Tatsuo Ishii <ishii at sraoss.co.jp> wrote:
>
> > 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..
>
> Hard to tell without knowing what Pgpool-II version you are using.
> Also a self contained test case would be useful.
>
> Best reagards,
> --
> Tatsuo Ishii
> SRA OSS LLC
> English: http://www.sraoss.co.jp/index_en/
> Japanese:http://www.sraoss.co.jp



-- 
thank u
               SADHU PRASAD