Re: updated SORT/LIMIT patch

"Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:

> Gregory Stark <stark(at)enterprisedb(dot)com> writes:
>> What does the executor do differently in the case of a subplan with a
>> parameter that makes it re-execute the plan from scratch and not just do a
>> simple rescan?
>
> Look at the chgParam signaling. Since a Sort node itself has no
> parameters, it historically has only had to re-sort if its input node
> suffers a parameter change, which it checks in ExecReScanSort. But now
> the bound effectively acts like a parameter, and has to force a
> recomputation.

Hm, that all makes sense now. But then there's something mysterious going on
still as the regression test I tried to write for this actually does work:

edb=# select (select ROW(int_array_aggregate(empno::integer),min(sal),round(avg(sal)),max(sal)) as sal from (select * from emp order by sal offset 3*bucket limit 3) as x) from generate_series(0,(select count(*) from emp)/3) as bucket;
LOG: begin tuple sort: nkeys = 1, workMem = 1024, randomAccess = f
LOG: switching to bounded heap sort at 7 tuples
LOG: performsort starting: CPU 0.00s/0.00u sec elapsed 0.00 sec
LOG: doing unheapify of 3 tuples
LOG: performsort done: CPU 0.00s/0.00u sec elapsed 0.00 sec
LOG: internal sort ended, 17 KB used: CPU 0.00s/0.00u sec elapsed 0.00 sec
LOG: begin tuple sort: nkeys = 1, workMem = 1024, randomAccess = f
LOG: switching to bounded heap sort at 13 tuples
LOG: performsort starting: CPU 0.00s/0.00u sec elapsed 0.00 sec
LOG: doing unheapify of 6 tuples
LOG: performsort done: CPU 0.00s/0.00u sec elapsed 0.00 sec
LOG: internal sort ended, 17 KB used: CPU 0.00s/0.00u sec elapsed 0.00 sec
LOG: begin tuple sort: nkeys = 1, workMem = 1024, randomAccess = f
LOG: performsort starting: CPU 0.00s/0.00u sec elapsed 0.00 sec
LOG: doing qsort of 14 tuples
LOG: performsort done: CPU 0.00s/0.00u sec elapsed 0.00 sec
LOG: internal sort ended, 18 KB used: CPU 0.00s/0.00u sec elapsed 0.00 sec
LOG: begin tuple sort: nkeys = 1, workMem = 1024, randomAccess = f
LOG: performsort starting: CPU 0.00s/0.00u sec elapsed 0.00 sec
LOG: doing qsort of 14 tuples
LOG: performsort done: CPU 0.00s/0.00u sec elapsed 0.00 sec
LOG: internal sort ended, 18 KB used: CPU 0.00s/0.00u sec elapsed 0.00 sec
LOG: begin tuple sort: nkeys = 1, workMem = 1024, randomAccess = f
LOG: performsort starting: CPU 0.00s/0.00u sec elapsed 0.00 sec
LOG: doing qsort of 14 tuples
LOG: performsort done: CPU 0.00s/0.00u sec elapsed 0.00 sec
LOG: internal sort ended, 18 KB used: CPU 0.00s/0.00u sec elapsed 0.00 sec
?column?
-------------------------------------------
("{7369,7900,7876}",800.00,950,1100.00)
("{7654,7521,7934}",1250.00,1267,1300.00)
("{7844,7499,7782}",1500.00,1850,2450.00)
("{7698,7566,7902}",2850.00,2942,3000.00)
("{7788,7839}",3000.00,4000,5000.00)
(5 rows)

--
Gregory Stark
EnterpriseDB http://www.enterprisedb.com