[pgpool-hackers: 1533] Re: Allow to access to pgpool while doing health checking
Muhammad Usama
m.usama at gmail.com
Wed May 4 05:37:05 JST 2016
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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