[pgpool-hackers: 1645] Re: kind does not match error in pgpool

[Muhammad Usama]

Hi Ishii-San

Can you please have a look at the attached patch, It try to solve this
"Kind does not match .." problem by ignoring the notice messages while
reading the backend response in read_kind_from_backend() function

Best Regards
Muhammad Usama





On Tue, Apr 19, 2016 at 1:50 PM, Ahsan Hadi <ahsan.hadi at enterprisedb.com>
wrote:

> I agree this cause lot of annoyance to pgpool users and something we
> should address for 3.6.
>
> Usama,
> Is this added to 3.6 wiki?
>
> On Fri, Apr 15, 2016 at 11:46 AM, Muhammad Usama <m.usama at gmail.com>
> wrote:
>
>> Hi
>>
>> pgpool throws ".. kind does not match.." error message when all the
>> attached backend nodes do not return the same response to the query. Although
>> this error message can be a symptom of the backend node sync issue in
>> most cases, but in case when the message kind of backend nodes differs
>> because one of the backend returned the notice response while the other
>> returned some other kind then that case should not be considered as an
>> error case.
>>
>> Consider the scenario where a pgpool is connected to three backend nodes
>> and pgpool is expecting to receive "[C] command complete" message from
>> all nodes for the last query. But while processing the query one of the
>> backend also produced a warning message.
>>
>> ... WARNING: database "testdb" must be vacuum within 11000000 transaction
>>
>> Please note that the query was successful on all attached backend, but
>> one backend also produced an extra warning message along with the command
>> complete message.
>>
>> Now pgpool will throw an error something like
>>
>> ERROR: pid 720: read_kind_from_backend: 1 th kind N does not match
>> with master or majority connection kind C
>>
>> But since the node would also have sent the expected command complete
>> message after that warning notice, So Ideally, pgpool should ignore the
>> WARNING message and compare the subsequent message, and only throw an error
>> if the message from nodes after ignoring notification messages differs.
>>
>> What are your thoughts on this?
>>
>> Kind regards
>> Muhammad Usama
>>
>>
>> _______________________________________________
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>> pgpool-hackers at pgpool.net
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>>
>>
>
>
> --
> Ahsan Hadi
> Snr Director Product Development
> EnterpriseDB Corporation
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diff --git a/src/protocol/pool_process_query.c b/src/protocol/pool_process_query.c
index 2625628..da88ac1 100644
--- a/src/protocol/pool_process_query.c
+++ b/src/protocol/pool_process_query.c
@@ -3334,32 +3334,43 @@ void read_kind_from_backend(POOL_CONNECTION *frontend, POOL_CONNECTION_POOL *bac
 						 errdetail("backend:%d kind:'%c'",i, kind)));
 
 				/*
-				 * Read and discard parameter status
+				 * Read and discard parameter status and notice messages
 				 */
-				if (kind != 'S')
+				if (kind == 'N')
 				{
-					break;
+					char *message = NULL;
+					if (pool_extract_error_message(false, CONNECTION(backend, i), MAJOR(backend), false, &message) == 1)
+					{
+						ereport(LOG,
+							(errmsg("Notice message received from backend %d while reading backend data packet kind",i),
+								 errdetail("message : \"%s\"",message)));
+						pfree(message);
+					}
 				}
-
-				pool_read(CONNECTION(backend, i), &len, sizeof(len));
-				len = htonl(len) - 4;
-				p = pool_read2(CONNECTION(backend, i), len);
-				if (p)
+				else if (kind == 'S')
 				{
-					value = p + strlen(p) + 1;
-					ereport(DEBUG1,
-						(errmsg("reading backend data packet kind"),
-							 errdetail("parameter name: %s value: \"%s\"", p, value)));
+					pool_read(CONNECTION(backend, i), &len, sizeof(len));
+					len = htonl(len) - 4;
+					p = pool_read2(CONNECTION(backend, i), len);
+					if (p)
+					{
+						value = p + strlen(p) + 1;
+						ereport(DEBUG1,
+							(errmsg("reading backend data packet kind"),
+								 errdetail("parameter name: %s value: \"%s\"", p, value)));
 
-					if (IS_MASTER_NODE_ID(i))
-						pool_add_param(&CONNECTION(backend, i)->params, p, value);
+						if (IS_MASTER_NODE_ID(i))
+							pool_add_param(&CONNECTION(backend, i)->params, p, value);
+					}
+					else
+					{
+						ereport(WARNING,
+							(errmsg("failed to read parameter status packet from backend %d", i),
+								 errdetail("read from backend failed")));
+					}
 				}
-				else
-					ereport(WARNING,
-						(errmsg("failed to read parameter status packet from backend %d", i),
-							 errdetail("read from backend failed")));
 
-			} while (kind == 'S');
+			} while (kind == 'S' || kind == 'N' );
 
 #ifdef DEALLOCATE_ERROR_TEST
 			if (i == 1 && kind == 'C' &&