Horton

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

Simon Riggs <simon@2ndquadrant.com>

View thread
From: Simon Riggs <simon@2ndQuadrant.com>
To: Andres Freund <andres@2ndquadrant.com>
Cc: pgsql-hackers@postgresql.org
Date: 2012-06-18T15:35:40Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Don't waste the last segment of each 4GB logical log file.

  2. Stamp HEAD as 9.3devel.

  3. Wake WALSender to reduce data loss at failover for async commit.

  4. Make the visibility map crash-safe.

On 13 June 2012 19:28, Andres Freund <andres@2ndquadrant.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/
 PostgreSQL Development, 24x7 Support, Training & Services