Re: Undo logs

On 24 May 2018 at 23:22, Thomas Munro <thomas.munro@enterprisedb.com> wrote:

> As announced elsewhere[1][2][3], at EnterpriseDB we are working on a
> proposal to add in-place updates with undo logs to PostgreSQL.  The
> goal is to improve performance and resource usage by recycling space
> better.

Cool

> The lowest level piece of this work is a physical undo log manager,

> 1.  Efficient appending of new undo data from many concurrent
> backends.  Like logs.
> 2.  Efficient discarding of old undo data that isn't needed anymore.
> Like queues.
> 3.  Efficient buffered random reading of undo data.  Like relations.

Like an SLRU?

> [4] https://github.com/EnterpriseDB/zheap/tree/undo-log-storage/src/backend/access/undo
> [5] https://github.com/EnterpriseDB/zheap/tree/undo-log-storage/src/backend/storage/smgr

I think there are quite a few design decisions there that need to be
discussed, so lets crack on and discuss them please.

-- 
Simon Riggs                http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services