Re: Core team statement on replication in PostgreSQL

Josh Berkus wrote:
> Bruce,
> 
> > Another idea I discussed with Tom is having the slave _delay_ applying
> > WAL files until all slave snapshots are ready.
> > 
> 
> Well, again, that only works for async mode.  I personally think that's 
> the correct solution for async.  But for synch mode, I think we need to 
> push the xids back to the master; generally if a user is running in 
> synch mode they're concerned about failover time and zero data loss, so 
> holding back the WAL files doesn't make sense.

You send the WAL to the slave, but the slave doesn't apply them right
away --- it isn't related to async.

> Also, if you did delay applying WAL files on an async slave, you'd reach 
> a point (perhaps after a 6-hour query) where it'd actually be cheaper to 
> rebuild the slave than to apply the pent-up WAL files.

True.

--  Bruce Momjian  <bruce@momjian.us>        http://momjian.us EnterpriseDB
http://enterprisedb.com
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