Re: Streaming replication status

On 9/01/2010 6:20 AM, Josh Berkus wrote:
> On 1/8/10 1:16 PM, Heikki Linnakangas wrote:
>> * A standby that connects to master, initiates streaming, and then sits
>> idle without stalls recycling of old WAL files in the master. That will
>> eventually lead to a full disk in master. Do we need some kind of a
>> emergency valve on that?
>
> WARNING: I haven't thought about how this would work together with HS yes.
>
> I think this needs to be administrator-configurable.
>
> I'd suggest a GUC approach:
>
> archiving_lag_action = { ignore, shutdown, stop }
>
> "Ignore" would be the default. Some users would rather have the master
> shut down if the slave has stopped taking segments; that's "shutdown".
> Otherwise, it's "stop" which simply stops archiving and starts recylcing
> when we reach that number of segments.

IMO "stop" would be *really* bad without some sort of administrator
alert support (scream for help) and/or the ability to refresh the
slave's base backup when it started responding again. We'd start seeing
mailing list posts along the lines of "my master failed over to the
slave, and it's missing the last 3 months of data! Help!".

Personally, I'd be uncomfortable enabling something like that without
_both_ an admin alert _and_ the ability to refresh the slave's base
backup without admin intervention.

It'd also be necessary to define what exactly "lag" means here,
preferably in a way that doesn't generally need admin tuning for most
users. Ideally there'd be separate thresholds for "scream to the admin
for help, something's wrong" and "forced to act, slave is holding up the
master".

--
Craig Ringer