Re: Proposal: Snapshot cloning

On Thu, 2007-01-25 at 22:19 -0500, Jan Wieck wrote:

> The idea is to clone an existing serializable transactions snapshot 
> visibility information from one backend to another. The semantics would 
> be like this:
> 
>      backend1: start transaction;
>      backend1: set transaction isolation level serializable;
>      backend1: select pg_backend_pid();
>      backend1: select publish_snapshot(); -- will block

Great idea. It can also be used by pg_dump to publish its snapshot so
that we can make VACUUM continue to process effectively while it pg_dump
is running.

Two questions:
- why does it have to block? I don't see any reason - the first process
can begin doing useful work. The second process might fail or itself be
blocked by something.

- why just serializable snapshots?

--  Simon Riggs              EnterpriseDB   http://www.enterprisedb.com