[pgpool-hackers: 1534] Re: Allow to access to pgpool while doing health checking
Tatsuo Ishii
ishii at postgresql.org
Wed May 4 09:53:36 JST 2016
Usama,
Thank you for testing the patch. Shall I commit/push it after you fix
the regression test issue? Or shall I commit/push it now? Either is
fine for me.
Best regards,
--
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
Japanese:http://www.sraoss.co.jp
> Hi Ishii-San
>
> I have tested the patch, It successfully takes care of the very annoying
> problem and it is working as expected.
>
> Best regards
> Muhammad Usama
>
>
> On Tue, May 3, 2016 at 5:25 PM, Tatsuo Ishii <ishii at postgresql.org> wrote:
>
>> Currently any attempt to connect to pgpool fails if pgpool is doing
>> health check against failed node even if fail_over_on_backend_error is
>> off because pgpool child first tries to connect to all backend
>> including the failed one and exits if it fails to connect to a backend
>> (of course it fails). This is a temporary situation and will be
>> resolved before pgpool executes failover. However if the health check
>> is retrying, the temporary situation keeps longer depending on the
>> setting of health_check_max_retries and health_check_retry_delay. This
>> is not good. Attached patch tries to mitigate the problem:
>>
>> - When an attempt to connect to backend fails, give up connecting to
>> the failed node and skip to other node, rather than exiting the
>> process if operating in streaming replication mode and the node is
>> not primary node.
>>
>> - Mark the local status of the failed node to "down".
>>
>> - This will let the primary node be selected as a load balance node
>> and every queries will be sent to the primary node. If there's other
>> healthy standby nodes, one of them will be chosen as the load
>> balance node.
>>
>> - After the session is over, the child process will suicide to not
>> retain the local status.
>>
>> Comments?
>> --
>> Tatsuo Ishii
>> SRA OSS, Inc. Japan
>> English: http://www.sraoss.co.jp/index_en.php
>> Japanese:http://www.sraoss.co.jp
>>
>> diff --git a/src/include/pool.h b/src/include/pool.h
>> index 4c6e82f..1f43efd 100644
>> --- a/src/include/pool.h
>> +++ b/src/include/pool.h
>> @@ -323,6 +323,7 @@ extern int my_master_node_id;
>> */
>> #define PRIMARY_NODE_ID (Req_info->primary_node_id >=0?\
>>
>> Req_info->primary_node_id:REAL_MASTER_NODE_ID)
>> +#define IS_PRIMARY_NODE_ID(node_id) (node_id == PRIMARY_NODE_ID)
>>
>> /*
>> * Real primary node id. If not in the mode or there's no primary
>> diff --git a/src/protocol/pool_connection_pool.c
>> b/src/protocol/pool_connection_pool.c
>> index b7cc946..7c33366 100644
>> --- a/src/protocol/pool_connection_pool.c
>> +++ b/src/protocol/pool_connection_pool.c
>> @@ -812,8 +812,8 @@ static POOL_CONNECTION_POOL_SLOT
>> *create_cp(POOL_CONNECTION_POOL_SLOT *cp, int s
>> }
>>
>> /*
>> - * create actual connections to backends
>> - * new connection resides in TopMemoryContext
>> + * Create actual connections to backends.
>> + * New connection resides in TopMemoryContext.
>> */
>> static POOL_CONNECTION_POOL *new_connection(POOL_CONNECTION_POOL *p)
>> {
>> @@ -851,12 +851,34 @@ static POOL_CONNECTION_POOL
>> *new_connection(POOL_CONNECTION_POOL *p)
>> ereport(FATAL,
>> (errmsg("failed to create a
>> backend connection"),
>> errdetail("executing
>> failover on backend")));
>> - }
>> + }
>> else
>> {
>> - ereport(FATAL,
>> - (errmsg("failed to create a
>> backend connection"),
>> - errdetail("not executing
>> failover because fail_over_on_backend_error is off")));
>> + /*
>> + * If we are in streaming replication mode
>> and the node is a
>> + * standby node, then we skip this node to
>> avoid fail over.
>> + */
>> + if (STREAM && !IS_PRIMARY_NODE_ID(i))
>> + {
>> + ereport(LOG,
>> + (errmsg("failed to
>> create a backend %d connection", i),
>> + errdetail("skip
>> this backend because because fail_over_on_backend_error is off and we are
>> in streaming replication mode and node is standby node")));
>> +
>> + /* set down status to local status
>> area */
>> + *(my_backend_status[i]) = CON_DOWN;
>> +
>> + /* make sure that we need to
>> restart the process after
>> + * finishing this session
>> + */
>> +
>> pool_get_my_process_info()->need_to_restart = 1;
>> + continue;
>> + }
>> + else
>> + {
>> + ereport(FATAL,
>> + (errmsg("failed to
>> create a backend %d connection", i),
>> + errdetail("not
>> executing failover because fail_over_on_backend_error is off")));
>> + }
>> }
>> child_exit(POOL_EXIT_AND_RESTART);
>> }
>> diff --git a/src/utils/pool_process_reporting.c
>> b/src/utils/pool_process_reporting.c
>> index 9b190c7..6cfd860 100644
>> --- a/src/utils/pool_process_reporting.c
>> +++ b/src/utils/pool_process_reporting.c
>> @@ -5,7 +5,7 @@
>> * pgpool: a language independent connection pool server for PostgreSQL
>> * written by Tatsuo Ishii
>> *
>> - * Copyright (c) 2003-2015 PgPool Global Development Group
>> + * Copyright (c) 2003-2016 PgPool Global Development Group
>> *
>> * Permission to use, copy, modify, and distribute this software and
>> * its documentation for any purpose and without fee is hereby
>>
>> _______________________________________________
>> pgpool-hackers mailing list
>> pgpool-hackers at pgpool.net
>> http://www.pgpool.net/mailman/listinfo/pgpool-hackers
>>
>>
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