Re: postgres hot-standby questions.

>
> Hello everyone,
>
> Two questions, grateful for any feedback anyone can share. They relate to
> switchover between master and hot-standby.
>
>
> 1. What exactly is the behaviour of the master/primary during shutdown
> when it has a hot standby?
>
> https://wiki.postgresql.org/wiki/Hot_Standby
> http://www.postgresql.org/docs/current/static/hot-standby.html
>
> If I shut down the master, then afterwards when it is finished, I shut
> down the standby, will they contain identical logical databases & WAL
> records, e.g. assuming possible network failure?
>
> i.e.
> - Is the primary shutdown delayed until it has received notice from the
> standby that all WAL has been received?    ( my guess is: no)
> - Is the primary shutdown delayed until it has received notice from the
> standby that all WAL has been applied?    ( my guess is: no)
> - Can the primary generate any new WAL (e.g. checkpoint) or logical data
> changes during the shutdown process that might not be sent to the standby?
>   (my guess is: no)
>
> For example,
> https://vibhorkumar.wordpress.com/2014/06/30/switchoverswitchback-in-postgresql-9-3/
> "With this patch, the walsender process tries to send all outstanding WAL
> records to the standby in replication when the user shuts down the
> master."
> "tries"?
>
> That page also makes it seem like you have to manually check the WAL
> status. (section 2)
> Is there any way to make the primary's completion of shutdown
> automatically synchronous with completion of WAL on standby(s)?


What you used for you repltación? aplication u other.

>
> 2. Let's assume for the moment I have some crazy reason to prefer to avoid
> rsync where possible, such as its historical weird behaviour on HFS+
> filesystems or its present unreliable heuristic for syncing hard-links or
> its default behaviour of not using checksums. Can a controlled switchover
> (not failover) be built on wal_keep_segments alone?
>
> wal_keep_segments could be set to a fairly high number, maybe 10000
> (160GB) to allow standby catchup even after a day. Let's assume here than
> 99% of maintenance takes less than an hour, and that we're keeping rsync
> as a fallback for the worst case.
>
> e.g. here's the whole switchover process...
>
> shutdown A (Master)
> shutdown B (Standby)
> (A and B  should be identical in terms of WAL and logical data at this
> point).
> swap M/S configurations around
> start B (Master)
>
> do some work on A for an hour
> finish work on A
>
> start A (Standby)
> A catches up with B from wal_keep_segments.
>
>
> shutdown B (Master)
> shutdown A (Standby)
> (A and B  should be identical in terms of WAL and logical data at this
> point).
> swap M/S configurations around
> start A (Master)
> start B (Standby)
>

Remeber init the slave igual firt moment.

> Graeme Bell
>
>
>
>
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Saludos,
Gilberto Castillo
La Habana, Cuba
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