Re: Inlining comparators as a performance optimisation

On Tue, Dec 6, 2011 at 4:23 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Robert Haas <robertmhaas@gmail.com> writes:
>> On Tue, Dec 6, 2011 at 1:07 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>>> I'll take another crack at it.  I'm not entirely sold yet on merging
>>> the two structs; I think first we'd better look and see what the needs
>>> are in the other potential callers I mentioned.  If we'd end up
>>> cluttering the struct with half a dozen weird fields, it'd be better to
>>> stick to a minimal interface struct with various wrapper structs, IMO.
>
>> OK.  I'll defer to whatever you come up with after looking at it.
>
> OK, it looks like nodeMergeAppend.c could use something exactly like the
> draft SortKey struct, while nodeMergejoin.c could embed such a struct in
> MergeJoinClauseData.  The btree stuff needs something more nearly
> equivalent to a ScanKey, including a datum-to-compare-to and a flags
> field.  I'm inclined to think the latter would be too specialized to put
> in the generic struct.  On the other hand, including the reverse and
> nulls_first flags in the generic struct is clearly a win since it allows
> ApplyComparator() to be defined as a generic function.  So the only
> thing that's really debatable is the attno field, and I'm not anal
> enough to insist on a separate level of struct just for that.
>
> I am however inclined to stick with the shortened struct name SortSupport
> rather than using SortKey.  The presence of the function pointer fields
> (especially the inlined-qsort pointers, assuming we adopt some form of
> Peter's patch) changes the struct's nature in my view; it's not really
> describing just a sort key (ie an ORDER BY column specification).

Works for me.  I think we should go ahead and get this part committed
first, and then we can look at the inlining stuff as a further
optimization for certain cases...

--
Robert Haas
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