Re: Why we lost Uber as a user

On Tue, Aug  2, 2016 at 10:33:15PM -0400, Bruce Momjian wrote:
> I saw from the Uber article that they weren't going to per-row logical
> replication but _statement_ replication, which is very hard to do
> because typical SQL doesn't record what concurrent transactions
> committed before a new statement's transaction snapshot is taken, and
> doesn't record lock order for row updates blocked by concurrent activity
> --- both of which affect the final result from the query.
> 
> So, for statement replication, it is not a question of whether the code
> has bugs, but that the replay is not 100% possible in all cases, unless
> you switch to some statement-row-lock hybrid ability.

Oh, and one more problem with statement-level replication is that the
overhead of statement replay is high, as high as it was on the master. 
That leaves minimal server resources left to handle read-only workloads
on the slave.

--  Bruce Momjian          http://momjian.us EnterpriseDB                             http://enterprisedb.com

+ As you are, so once was I. As I am, so you will be. +
+                     Ancient Roman grave inscription +