Re: WIP: further sorting speedup

"Luke Lonergan" <llonergan(at)greenplum(dot)com> writes:
> So you know, we=B9ve done some more work on the external sort to remove the
> =B3tape=B2 abstraction from the code, which makes a significant improvement.

Improvement where? That code's down in the noise so far as I can tell.
I see results like this (with the patched code):

CPU: P4 / Xeon with 2 hyper-threads, speed 2793.08 MHz (estimated)
Counted GLOBAL_POWER_EVENTS events (time during which processor is not stopped)
with a unit mask of 0x01 (mandatory) count 240000
samples % symbol name
147310 31.9110 tuplesort_heap_siftup
68381 14.8130 comparetup_index
34063 7.3789 btint4cmp
22573 4.8899 AllocSetAlloc
19317 4.1845 writetup_index
18953 4.1057 tuplesort_gettuple_common
18100 3.9209 mergepreread
17083 3.7006 GetMemoryChunkSpace
12527 2.7137 LWLockAcquire
11686 2.5315 LWLockRelease
6172 1.3370 tuplesort_heap_insert
5392 1.1680 index_form_tuple
5323 1.1531 PageAddItem
4943 1.0708 LogicalTapeWrite
4525 0.9802 LogicalTapeRead
4487 0.9720 LockBuffer
4217 0.9135 heapgettup
3891 0.8429 IndexBuildHeapScan
3862 0.8366 ltsReleaseBlock

It appears that a lot of the cycles blamed on tuplesort_heap_siftup are
due to cache misses associated with referencing memtuples[] entries
that have fallen out of L2 cache. Not sure how to improve that though.

regards, tom lane