On Fri, Nov 15, 2013 at 3:03 AM, Heikki Linnakangas <hlinnakan...@vmware.com > wrote:
> On 14.11.2013 14:38, David Rowley wrote: > >> I've just completed some more benchmarking of this. I didn't try dropping >> the threshold down to 2 or 0 but I did tests at the cut over point and >> really don't see much difference in performance between the list at 32 and >> the hashtable at 33 sequences. The hash table version excels in the 16000 >> sequence test in comparison to the unpatched version. >> >> Times are in milliseconds of the time it took to call currval() 100000 >> times for 1 sequence. >> Patched Unpatched increased by 1 in cache 1856.452 1844.11 -1% 32 >> in >> cache 1841.84 1802.433 -2% 33 in cache 1861.558 not tested N/A 16000 in >> cache 1963.711 10329.22 426% >> > > If I understand those results correctly, the best case scenario with the > current code takes about 1800 ms. There's practically no difference with N > <= 32, where N is the number of sequences touched. The hash table method > also takes about 1800 ms when N=33. The performance of the hash table is > O(1), so presumably we can extrapolate from that that it's the same for any > N. > > I think that means that we should just completely replace the list with > the hash table. The difference with a small N is lost in noise, so there's > no point in keeping the list as a fast path for small N. That'll make the > patch somewhat simpler. > - Heikki > I had thought that maybe the biggest type of workloads might only touch 1 or 2 sequences, though it may be small but I had thought there would be an overhead in both cycles and memory usage in creating a hash table for these light usages of sequence backends. It would certainly make the patch more simple by removing this and it would also mean that I could remove the sometimes unused ->next member from the SeqTableData struct which is just now set to NULL when in hash table mode. If you think it's the way to go then I can make the change, though maybe I'll hold off the refactor for now as it looks like other ideas have come up around rel cache. Regards David Rowley