[pgpool-general: 8780] Re: Difference between pgpool 'primary' and Watchdog 'MASTER' versus the 'load_balance_node'
Tatsuo Ishii
ishii at sraoss.co.jp
Mon May 29 17:40:31 JST 2023
>> Hi pgpool experts,
>>
>> Can you please clarify the below?
>> *During failover, Is the '*primary*' or '*MASTER*' or ' *load_balance_node*
>> failure taken into account?*
>
> It's hard to answer your question as the question is too vague. Anyway I try it...
>
> - primary failure is taken into account because it triggers failover.
> See https://www.pgpool.net/docs/44/en/html/runtime-config-failover.html for more details.
>
> - MASTER and other watchdog nodes are taken into account in failover.
> See
> https://www.pgpool.net/docs/44/en/html/runtime-watchdog-config.html#CONFIG-WATCHDOG-FAILOVER-BEHAVIOR
> for more details.
>
> - Load balance node is not taken into account in streaming replication mode.
> See note #2 in https://www.pgpool.net/docs/44/en/html/runtime-config-failover.html for more details.
Sorry, I meant "Load balance node is taken into account".
>>
>> *Thanks*
>> *Gopi*
>>
>>
>> On Tue, May 16, 2023 at 10:56 AM Gopikrishnan <nksgopikrishnan at gmail.com>
>> wrote:
>>
>>> Thank you for your response!
>>>
>>> Can you also kindly clarify this:
>>> During failover, Is the '*primary*' or '*MASTER*' or '
>>> *load_balance_node* failure taken into account?
>>>
>>> *Thanks*
>>> *Gopi*
>>>
>>>
>>> On Tue, May 16, 2023 at 10:26 AM Bo Peng <pengbo at sraoss.co.jp> wrote:
>>>
>>>> Hi,
>>>>
>>>> > Regd. which I couldn't gather much from the docs at:
>>>> > https://www.pgpool.net/docs/pgpool-II-4.0.4/
>>>> >
>>>> >
>>>> > 1. primary
>>>> > 2. MASTER
>>>> > 3. load_balance_node
>>>>
>>>> 1. primary:
>>>> It is the role of *PostgreSQL* nodes.
>>>> The role of PostgreSQL nodes can be primary or standby
>>>> in streaming replication mode.
>>>>
>>>> 2. MASTER:
>>>> I think you are asking the status name shown
>>>> in the result of pcp_watchdog_info command.
>>>> The status name MASTER/STANDBY is the role of *Pgpool-II* node.
>>>> If you have multiple Pgpool-II nodes using watchdog feature,
>>>> one of them will be elected as MASTER and others will be STANDBY.
>>>>
>>>> 3. load_balance_node
>>>> Pgpool-II supports for load balancing of SELECT queries.
>>>> When a session starts, pgpool will randomly elect one PostgreSQL node
>>>> as the load balance node (load_balance_node) and routes SELECTs to
>>>> the load_balance_node.
>>>>
>>>> On Mon, 15 May 2023 15:54:53 +0530
>>>> Gopikrishnan <nksgopikrishnan at gmail.com> wrote:
>>>>
>>>> > Hi folks,
>>>> >
>>>> > Need your help in clearing a confusion regd. basic terminologies:
>>>> >
>>>> > Regd. which I couldn't gather much from the docs at:
>>>> > https://www.pgpool.net/docs/pgpool-II-4.0.4/
>>>> >
>>>> >
>>>> > 1. primary
>>>> > 2. MASTER
>>>> > 3. load_balance_node
>>>> >
>>>> > I have a pgpool with 3 nodes. I have a confusion between the pgpool
>>>> primary and
>>>> > the watchdog *MASTER* and the `*load_balance_node*`
>>>> >
>>>> > In my setup, the pgpool primary node (according to show pool_nodes
>>>> output)
>>>> > is : *10.108.104.31, *and also the node designated *load_balance_node*.
>>>> >
>>>> > While the MASTER node, according to pgpool watchdog, is:
>>>> *10.108.104.32* And
>>>> > the *cluster virtual IP* is attached to this node.
>>>> >
>>>> > I have the following questions in mind:
>>>> >
>>>> >
>>>> > 1. What do the terms '*primary*' and '*MASTER*' and
>>>> *load_balance_node*
>>>> > mean?
>>>> > 2. During failover, Is the '*primary*' or '*MASTER*' or '
>>>> > *load_balance_node* failure taken into account?
>>>> > 3. What is the difference (or any relation) between the '*primary*'
>>>> and '
>>>> > *MASTER*' and *load_balance_node* nodes?
>>>> > 4. If the cluster virtual IP is on the non '*primary*' node,
>>>> wouldn't it
>>>> > affect the performance of the HA setup?
>>>> >
>>>> > Below are the outputs for *show pool_nodes *and* watchdog *info:
>>>> >
>>>> > psql -h delegateIP -p 9999 -U pgpool postgres -c "show pool_nodes"
>>>> > Password for user pgpool:
>>>> > node_id | hostname | port | status | lb_weight | role |
>>>> > select_cnt | load_balance_node | replication_delay |
>>>> >
>>>> last_status_change---------+---------------+------+--------+-----------+---------+------------+-------------------+-------------------+---------------------
>>>> > 0 | 10.108.104.31 | 5432 | up | 0.333333 | primary | 0
>>>> > | true | 0 | 2023-05-12 12:07:13
>>>> > 1 | 10.108.104.32 | 5432 | up | 0.333333 | standby | 0
>>>> > | false | 0 | 2023-05-12 12:07:13
>>>> > 2 | 10.108.104.33 | 5432 | down | 0.333333 | standby | 0
>>>> > | false | 0 | 2023-05-12 12:07:13
>>>> > (3 rows)
>>>> >
>>>> > And the Watchdog info:
>>>> >
>>>> > pcp_watchdog_info -h localhost -vw -U pgpool
>>>> > Watchdog Cluster Information
>>>> > Total Nodes : 3
>>>> > Remote Nodes : 2
>>>> > Quorum state : QUORUM EXIST
>>>> > Alive Remote Nodes : 2
>>>> > VIP up on local node : NO
>>>> > Master Node Name : vm-104-32.eng.dev.com:9999 Linux
>>>> vm-104-32.eng.dev.com
>>>> > Master Host Name : 10.108.104.32
>>>> >
>>>> > Watchdog Node Information
>>>> > Node Name : vm-104-31.eng.dev.com:9999 Linux vm-104-31.eng.dev.com
>>>> > Host Name : vm-104-31.eng.dev.com
>>>> > Delegate IP : 10.108.104.34
>>>> > Pgpool port : 9999
>>>> > Watchdog port : 9000
>>>> > Node priority : 1
>>>> > Status : 7
>>>> > Status Name : STANDBY
>>>> >
>>>> > Node Name : vm-104-32.eng.dev.com:9999 Linux vm-104-32.eng.dev.com
>>>> > Host Name : 10.108.104.32
>>>> > Delegate IP : 10.108.104.34
>>>> > Pgpool port : 9999
>>>> > Watchdog port : 9000
>>>> > Node priority : 1
>>>> > Status : 4
>>>> > Status Name : MASTER
>>>> >
>>>> > Node Name : vm-104-33.eng.dev.com:9999 Linux vm-104-33.eng.dev.com
>>>> > Host Name : 10.108.104.33
>>>> > Delegate IP : 10.108.104.34
>>>> > Pgpool port : 9999
>>>> > Watchdog port : 9000
>>>> > Node priority : 1
>>>> > Status : 7
>>>> > Status Name : STANDBY
>>>> >
>>>> >
>>>> >
>>>> > *Thanks & Regards*
>>>> > *Gopi*
>>>>
>>>>
>>>> --
>>>> Bo Peng <pengbo at sraoss.co.jp>
>>>> SRA OSS LLC
>>>> https://www.sraoss.co.jp/
>>>>
>>>
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