Re: logical changeset generation v6

On 09/20/2013 06:33 AM, Andres Freund wrote:
> Hi,
>

> The points I find daunting are the semantics, like:
> * How do we control whether a standby is allowed prevent WAL file
> removal. What if archiving is configured?
> * How do we control whether a standby is allowed to peg xmin?
> * How long do we peg an xmin/wal file removal if the standby is gone
> * How does the userinterface look to remove a slot if a standby is gone
> * How do we decide/control which commands use a slot in which cases?

I think we are going to want to be flexible enough to support users with
a couple of different points of use-cases.
* Some people will want to keep xmin pegged and prevent WAL removal so a
standby with a slot can always catch up, and wi
* Most people will want to say keep X megabytes of WA (if needed by a
behind slot) and keep xmin pegged so that the WAL can be consumed by a
logical plugin.

I can see us also implementing a restore_command that the walsender
could use to get archived segments but for logical replication xmin
would still need to be low enough

I don't think the current patch set is incompatible with us later
implementing any of the above. I'd rather see us focus on getting the
core functionality committed and worry about a good interface for
managing slots later.

> Greetings, Andres Freund

Steve