Re: [COMMITTERS] pgsql: Keep track of transaction commit timestamps

On 12/19/2014 11:30 AM, Petr Jelinek wrote:
> as promised I am sending code-comment patch that explains the use of
> commit timestamps + nodeid C api for the conflict resolution, comments
> welcome.

That's a little bit better, but I have to say I'm still not impressed. 
There are so many implicit assumptions in the system. The first 
assumption is that a 32-bit node id is sufficient. I'm sure it is for 
many replication systems, but might not be for all. Then there's the 
assumption that the node id should be "sticky", i.e. it's set for the 
whole session. Again, I'm sure that's useful for many systems, but I 
could just as easily imagine that you'd want it to reset after every commit.

To be honest, I think this patch should be reverted. Instead, we should 
design a system where extensions can define their own SLRUs to store 
additional per-transaction information. That way, each extension can 
have as much space per transaction as needed, and support functions that 
make most sense with the information. Commit timestamp tracking would be 
one such extension, and for this node ID stuff, you could have another 
one (or include it in the replication extension).

- Heikki