Re: [PATCH] Push limit to sort through a subquery

>
> No.  You can't easily avoid recursion for the merge-append case, since
> that has to descend to multiple children.


Agreed. That's why it's not in the while loop in my sketch of the suggested
rework.


>   TBH I dislike the fact that
> you did the subquery case randomly differently from the existing cases;
> it should just have been added as an additional recursive case.  Since
> this is done only once at query startup, worrying about hypothetical
> micro-performance issues seems rather misguided.
>

Habit mostly - why write code with potential performance problems when the
alternative is just as easy to read?

I disagree with saying "it's just done at query startup so don't worry
about it too much". Back in my days with DB2 we were working on the TPCC
benchmark (when it was still relevant) and we found that the startup cost
was a huge factor when doing rapid fire, cached, simple queries. In many
cases the startup cost was >50% of the overall query execution time. Our
testing here in Salesforce is showing a similar pattern in some of our
workloads and PostgreSQL.

I'm not trying to argue that this particular issue of recurse/don't recurse
is going to make or break anything. It's just where my head's at when I
look at the code.

- Doug
Salesforce