Re: [PATCH 10/16] Introduce the concept that wal has a 'origin' node

On 13 June 2012 19:28, Andres Freund <andres(at)2ndquadrant(dot)com> wrote:

> This adds a new configuration parameter multimaster_node_id which determines
> the id used for wal originating in one cluster.

Looks good and it seems this aspect at least is commitable in this CF.

Design decisions I think we need to review are

* Naming of field. I think origin is the right term, borrowing from Slony.

* Can we add the origin_id dynamically to each WAL record? Probably no
need, but lets consider why and document that.

* Size of field. 16 bits is enough for 32,000 master nodes, which is
quite a lot. Do we need that many? I think we may have need for a few
flag bits, so I'd like to reserve at least 4 bits for flag bits, maybe
8 bits. Even if we don't need them in this release, I'd like to have
them. If they remain unused after a few releases, we may choose to
redeploy some of them as additional nodeids in future. I don't foresee
complaints that 256 master nodes is too few anytime soon, so we can
defer that decision.

* Do we want origin_id as a parameter or as a setting in pgcontrol?
IIRC we go to a lot of trouble elsewhere to avoid problems with
changing on/off parameter values. I think we need some discussion to
validate where that should live.

* Is there any overhead from CRC of WAL record because of this? I'd
guess not, but just want to double check thinking.

Presumably there is no issue wrt Heikki's WAL changes? I assume not,
but ask since I know you're reviewing that also.

--
 Simon Riggs                   http://www.2ndQuadrant.com/
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