[pgpool-hackers: 2006] Re: Proposal to make backend node failover mechanism quorum aware

[Ahsan Hadi]

On Wed, Jan 25, 2017 at 12:11 PM, Ahsan Hadi <ahsan.hadi at enterprisedb.com>
wrote:

>
>
> On Wed, Jan 25, 2017 at 9:22 AM, Tatsuo Ishii <ishii at sraoss.co.jp> wrote:
>
>> > You can also understand "auto-failover" as preserving the connection.
>> Right
>> > now if you have a connection with a master and a stand-by node, the
>> pgpool
>> > "show pool_nodes" gives you this...
>> >
>> > [ec2-user at ip-172-25-1-32 bin]$ ./edb-psql  edb -p 9999 -U ec2-user
>> >
>> > edb-psql (9.6.1.6, server 9.5.3.8)
>> >
>> > Type "help" for help.
>> >
>> > edb=# show pool_nodes;
>> >
>> >  node_id |  hostname   | port | status | lb_weight |  role   |
>> select_cnt |
>> > load_balance_node | replication_delay
>> >
>> > ---------+-------------+------+--------+-----------+--------
>> -+------------+-------------------+-------------------
>> >
>> >  0       | 172.25.1.33 | 5444 | up     | 0.500000  | primary | 0
>>   |
>> > false             | 0
>> >
>> >  1       | 172.25.1.34 | 5444 | up     | 0.500000  | standby | 0
>>   |
>> > true              | 0
>> > (2 rows)
>> >
>> > if you bring down the stand-by node, the health-check will kick in and
>> if
>> > you run the same query again it will fail.
>>
>> That's only happens if the client uses the standby.
>>
>
> Correct...After the feature you added to 3.6, if a standby fails that is
> not being used by the client, the client won't be affected. That was good
> step in the right direction. The next step is that if the stand-by fails
> and the master is still available the client is still not affected, that's
> what i am proposing...
>
>
>>
>> > What i mean by auto-failover is if the master (primary server) is
>> > available, the auto-failover feature should failover to the master
>> instead
>> > of throwing an error.
>> >
>> > Does that make sense?
>>
>> To make it possible we need to think about followings:
>>
>> 1) We need to migrate all the session properties set in the previous
>>    session to the new master connection.
>>
>> 2) If the client was receiving data row from Pgpool-II, it's hard to
>>    continue it in the new session.
>>
>> 3) If the client was in the middle of a transaction, it's hard to
>>    continue it in the new session.
>>
>> These are not trivial, and I think it's not worth the problem, to be
>> honest.
>>
>
> Well i think it is debatable whether the feature is worth the effort of
> not. It affects an application continuity to work if we don't have the
> complete auto-failover feature. Do you think it becomes less complex of we
> don't provide 3 in the first phase?
>

Btw this is similar functionality that Oracle offers called Transparent
Application Failover (TAF)...

>
>
>>
>> Best regards,
>> --
>> Tatsuo Ishii
>> SRA OSS, Inc. Japan
>> English: http://www.sraoss.co.jp/index_en.php
>> Japanese:http://www.sraoss.co.jp
>>
>
>
>
> --
> Ahsan Hadi
> Snr Director Product Development
> EnterpriseDB Corporation
> The Enterprise Postgres Company
>
> Phone: +92-51-8358874 <(051)%208358874>
> Mobile: +92-333-5162114 <0333%205162114>
>
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-- 
Ahsan Hadi
Snr Director Product Development
EnterpriseDB Corporation
The Enterprise Postgres Company

Phone: +92-51-8358874
Mobile: +92-333-5162114

Website: www.enterprisedb.com
EnterpriseDB Blog: http://blogs.enterprisedb.com/
Follow us on Twitter: http://www.twitter.com/enterprisedb

This e-mail message (and any attachment) is intended for the use of the
individual or entity to whom it is addressed. This message contains
information from EnterpriseDB Corporation that may be privileged,
confidential, or exempt from disclosure under applicable law. If you are
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