Re: Fast switchover
| От | Ron Johnson |
|---|---|
| Тема | Re: Fast switchover |
| Дата | |
| Msg-id | CANzqJaDPo-tLSZuOLxTic1yx-=X7EuXS8X9f22aD92-D4RDrYw@mail.gmail.com обсуждение исходный текст |
| Ответ на | Fast switchover (legrand legrand <legrand_legrand@hotmail.com>) |
| Ответы |
RE: Fast switchover
|
| Список | pgsql-general |
On Mon, Sep 8, 2025 at 11:03 AM legrand legrand <legrand_legrand@hotmail.com> wrote:
Hello all the readers,For some projects we need a fast manual switchover to address Near Zero downtime maintenance(not speaking here about automated failover like those provided by HA tools, but just planned, controlled operations)Database Physical replication switchover itself:- initial replication (before switchover) should be synchronous or replication LAG should be controlled to prevent data loss.- Switchover duration seems not "compressible" under a few seconds (because of primary shutdown, promotion, new standby catch up, ...)- Application retry strategy (after disconnection) should be tuned using proper retry delay. Pooler or specific driver may help.
There will always be a few seconds delay while the applications reconnect.
Do the applications connect via a VIP? That's simpler for the application.
This is what I do from the not-yet-new-primary:
- psql -h $CurrentPrimary -c "ALTER SYSTEM SET synchronous_standby_names TO '*';"
- Wait a few seconds.
- ssh $CurrentPrimary sudo ip del $VIP # cmd is more complicated, but you get the idea
- ssh $CurrentPrimary pg_ctl stop -mfast # to kill connections, has to happen, no matter the solution.
- pg_ctl promote
- sudo ip add $VIP
- Replicate from new-primary to new-replica "at leisure".
No retry delay, since the application directly goes to the new server.
Steps 3-6 are in a script, and what pgpool does, except I do it. #4 is by far the slowest. ssh authentication delay in #3 and #4 are nonexistent if you have "pre-created" an ssh socket.
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