Re: proposal: CREATE DATABASE vs. (partial) CHECKPOINT

Heikki Linnakangas <hlinnakangas@vmware.com> writes:
> On 10/27/2014 03:21 PM, Tomas Vondra wrote:
>> Thinking about this a bit more, do we really need a full checkpoint? That
>> is a checkpoint of all the databases in the cluster? Why checkpointing the
>> source database is not enough?

> A full checkpoint ensures that you always begin recovery *after* the 
> DBASE_CREATE record. I.e. you never replay a DBASE_CREATE record during 
> crash recovery (except when you crash before the transaction commits, in 
> which case it doesn't matter if the new database's directory is borked).

Yeah.  After re-reading the 2005 thread, I wonder if we shouldn't just
bite the bullet and redesign CREATE DATABASE as you suggest, ie, WAL-log
all the copied files instead of doing a "cp -r"-equivalent directory copy.
That would fix a number of existing replay hazards as well as making it
safe to do what Tomas wants.  In the small scale this would cause more I/O
(2 copies of the template database's data) but in production situations
we might well come out ahead by avoiding a forced checkpoint of the rest
of the cluster.  Also I guess we could skip WAL-logging if WAL archiving
is off, similarly to the existing optimization for CREATE INDEX etc.
        regards, tom lane