Re: WIP: expression evaluation improvements

Hi,

On 2021-11-05 09:48:16 -0700, Andres Freund wrote:
> On 2021-11-05 08:34:26 -0400, Robert Haas wrote:
> > I'm not sure why that requires all of this relative pointer stuff,
> > honestly. Under that problem statement, we don't need everything to be
> > one contiguous allocation. We just need it to have the same lifespan
> > as the JITted code.  If you introduced no relative pointers at all,
> > you could still solve this problem: create a new memory context that
> > contains all of the EvalExprSteps and all of the allocations upon
> > which they depend, make sure everything you care about is allocated in
> > that context, and don't destroy any of it until you destroy it all.
> 
> I don't see how that works - the same expression can be evaluated multiple
> times at once, recursively. So you can't have things like FunctionCallInfoData
> shared. One key point of separating out the mutable data into something that
> can be relocated is precisely so that every execution can have its own
> "mutable" data area, without needing to change anything else.

Oh, and the other bit is that the absolute addresses make it much harder to
generate efficient code. If I remove the code setting
FunctionCallInfo->{context,flinfo} to the constant pointers (obviously
incorrect, but works for functions not using either), E.g. TPCH-Q1 gets about
20% faster.

Greetings,

Andres Freund