[pgpool-general: 8777] Re: Difference between pgpool 'primary' and Watchdog 'MASTER' versus the 'load_balance_node'

[Gopikrishnan]

Hi pgpool experts,

Can you please clarify the below?
*During failover, Is the '*primary*' or '*MASTER*' or ' *load_balance_node*
failure 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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