Re: Update on sort-compression stuff

Martijn van Oosterhout <kleptog@svana.org> writes:
> - Test a way of storing tuples with less overhead than a HeapTuple
> header. If you could do it for in-memory sorts, that'd mean you could
> fit more tuples in memory before spilling to disk. Given the
> "compression" in that case is extremely cheap, it'd be much more likely
> to be beneficial.

I looked into this and decided that trimming the headers for the
in-memory copies is not as attractive as all that.  The killer problem
is that comparetup_heap() needs to be able to apply heap_getattr() to
the stored tuples to extract sort keys.  Unless we want to support a
variant copy of the heap_getattr() infrastructure just for sort tuples,
it ain't gonna work.  Another issue is that we'd be increasing the
palloc traffic for in-memory sorts, because tuplesort_gettuple() would
have to cons up a freshly palloc'd complete tuple to hand back to the
caller.

However, we can definitely trim a lot of overhead from what gets written
to "tape", so I'll have a go at doing that.
        regards, tom lane