Hi, On 2019-03-02 18:11:43 -0500, Tom Lane wrote: > I wonder what test cases Andres has been looking at that convince > him that we need a reimplementation of Lists.
My main observation was from when the expression evaluation was using lists all over. List iteration overhead was very substantial there. But that's not a problem anymore, because all of those are gone now due to the expression rewrite. I personally wasn't actually advocating for a new list implementation, I was/am advocating that we should move some tasks over to a more optimized representation. I still regularly see list overhead matter in production workloads. A lot of it being memory allocator overhead, which is why I'm concerned with a rewrite that doesn't reduce the number of memory allocations. And a lot of it is stuff that you won't see in pgbench - e.g. there's a lot of production queries that join a bunch of tables with a few dozen columns, where e.g. all the targetlists are much longer than what you'd see in pgbench -S. Greetings, Andres Freund
