Hey there, reviving this thread. To clarify: In order to show this patch is worth doing, I should index a bunch of natural-language documents (whichever language that is) and show that the patch brings a performance benefit?
(Just clarifying, because at least inside ElasticSearch for the logs use-case, it turns out that it does provide a performance benefit -- but I want to make sure I understand what the Lucene community wishes to see as "evidence" this is worth pursuing :-) Cheers, Thomas On Tue, Apr 25, 2023 at 8:14 PM Walter Underwood <wun...@wunderwood.org> wrote: > I would recommend some non-English tests. Non-Latin scripts (CJK, Arabic, > Hebrew) will have longer byte strings because of UTF8. German has large > compound words. > > wunder > Walter Underwood > wun...@wunderwood.org > http://observer.wunderwood.org/ (my blog) > > On Apr 25, 2023, at 10:57 AM, Thomas Dullien > <thomas.dull...@elastic.co.INVALID> wrote: > > Hey all, > > ok, attached is a second patch that adds some unit tests; I am happy to > add more. > > This brings me back to my original question: I'd like to run some pretty > thorough benchmarking on Lucene, both for this change and for possible > other future changes, largely focused on indexing performance. What are > good command lines to do so? What are good corpora? > > Cheers, > Thomas > > On Tue, Apr 25, 2023 at 6:04 PM Thomas Dullien <thomas.dull...@elastic.co> > wrote: > >> Hey, >> >> ok, I've done some digging: Unfortunately, MurmurHash3 does not publish >> official test vectors, see the following URLs: >> https://github.com/aappleby/smhasher/issues/6 >> >> https://github.com/multiformats/go-multihash/issues/135#issuecomment-791178958 >> There is a link to a pastebin entry in the first issue, which leads to >> https://pastebin.com/kkggV9Vx >> >> Now, the test vectors in that pastebin do not match either the output of >> pre-change Lucene's murmur3, nor the output of the Python mmh3 package. >> That said, the pre-change Lucene and the mmh3 package agree, just not with >> the published list. >> >> There *are* test vectors in the source code for the mmh3 python package, >> which I could use, or cook up a set of bespoke ones, or both (I share the >> concern about 8-byte boundaries and signedness). >> >> https://github.com/hajimes/mmh3/blob/3bf1e5aef777d701305c1be7ad0550e093038902/test_mmh3.py#L75 >> >> Cheers, >> Thomas >> >> On Tue, Apr 25, 2023 at 5:15 PM Robert Muir <rcm...@gmail.com> wrote: >> >>> i dont think we need a ton of random strings. But if you want to >>> optimize for strings of length 8, at a minimum there should be very >>> simple tests ensuring correctness for some boundary conditions (e.g. >>> string of length exactly 8). i would also strongly recommend testing >>> non-ascii since java is a language with signed integer types so it may >>> be susceptible to bugs where the input bytes have the "sign bit" set. >>> >>> IMO this could be 2 simple unit tests. >>> >>> usually at least with these kinds of algorithms you can also find >>> published "test vectors" that intend to seek out the corner cases. if >>> these exist for murmurhash, we should fold them in too. >>> >>> On Tue, Apr 25, 2023 at 11:08 AM Thomas Dullien >>> <thomas.dull...@elastic.co> wrote: >>> > >>> > Hey, >>> > >>> > I offered to run a large number of random-string-hashes to ensure that >>> the output is the same pre- and post-change. I can add an arbitrary number >>> of such tests to TestStringHelper.java, just specify the number you wish. >>> > >>> > If your worry is that my change breaches the inlining bytecode limit: >>> Did you check whether the old version was inlineable or not? The new >>> version is 263 bytecode instructions, the old version was 110. The default >>> inlining limit appears to be 35 bytecode instructions on cursory checking >>> (I may be wrong on this, though), so I don't think it was ever inlineable >>> in default configs. >>> > >>> > On your statement "we haven't seen performance gains" -- the starting >>> point of this thread was a friendly request to please point me to >>> instructions for running a broad range of Lucene indexing benchmarks, so I >>> can gather data for further discussion; from my perspective, we haven't >>> even gathered any data, so obviously we haven't seen any gains. >>> > >>> > Cheers, >>> > Thomas >>> > >>> > On Tue, Apr 25, 2023 at 4:27 PM Robert Muir <rcm...@gmail.com> wrote: >>> >> >>> >> There is literally one string, all-ascii. This won't fail if all the >>> >> shifts and masks are wrong. >>> >> >>> >> About the inlining, i'm not talking about cpu stuff, i'm talking about >>> >> java. There are limits to the size of methods that get inlined (e.g. >>> >> -XX:MaxInlineSize). If we make this method enormous like this, it may >>> >> have performance consequences. >>> >> >>> >> We still haven't seen any performance gain from this. Elasticsearch >>> >> putting huge unique IDs into indexed terms doesnt count. >>> >> >>> >> On Tue, Apr 25, 2023 at 10:25 AM Thomas Dullien >>> >> <thomas.dull...@elastic.co> wrote: >>> >> > >>> >> > Hey, >>> >> > >>> >> > so there are unit tests in TestStringHelper.java that test strings >>> of length greater than 8, and my change passes them. Could you explain what >>> you want tested? >>> >> > >>> >> > Cheers, >>> >> > Thomas >>> >> > >>> >> > On Tue, Apr 25, 2023 at 4:21 PM Robert Muir <rcm...@gmail.com> >>> wrote: >>> >> >> >>> >> >> sure, but "if length > 8 return 1" might pass these same tests too, >>> >> >> yet cause a ton of hash collisions. >>> >> >> >>> >> >> I just think if you want to optimize for super-long strings, there >>> >> >> should be a unit test. >>> >> >> >>> >> >> On Tue, Apr 25, 2023 at 10:20 AM Thomas Dullien >>> >> >> <thomas.dull...@elastic.co> wrote: >>> >> >> > >>> >> >> > Hey, >>> >> >> > >>> >> >> > I am pretty confident about correctness. The change passes both >>> Lucene and ES regression tests and my careful reading of the code is pretty >>> certain that the output is the same. If you want me to randomly test the >>> result for a few hundred million random strings, I'm happy to do that, too, >>> if you have other suggestions for correctness testing, let me know. >>> >> >> > >>> >> >> > The change does increase the method size and may impact inlining >>> - but so does literally any code change, particularly in a JIT'ed >>> environment where placement of code (and hence things like instruction >>> cache conflicts) depend on the precise history of execution. The way I >>> understand it, one deals with this by benchmarking and measuring. >>> >> >> > >>> >> >> > FWIW, several indexing-heavy ES benchmarks show a noticeable >>> improvement in indexing speed - this is why I was asking about a broad >>> range of Lucene benchmarks; to verify that this is indeed the case for >>> Lucene-only, too. >>> >> >> > >>> >> >> > Let me know what data you'd like to see to decide whether this >>> patch is a good idea, and if there is consensus among the Lucene committers >>> that those are reasonable criteria, I'll work on producing that data. >>> >> >> > >>> >> >> > Cheers, >>> >> >> > Thomas >>> >> >> > >>> >> >> > >>> >> >> > >>> >> >> > On Tue, Apr 25, 2023 at 4:02 PM Robert Muir <rcm...@gmail.com> >>> wrote: >>> >> >> >> >>> >> >> >> well there is some cost, as it must add additional checks to >>> see if >>> >> >> >> its longer than 8. in your patch, additional loops. it >>> increases the >>> >> >> >> method size and may impact inlining and other things. also we >>> can't >>> >> >> >> forget about correctness, if the hash function does the wrong >>> thing it >>> >> >> >> could slow everything to a crawl. >>> >> >> >> >>> >> >> >> On Tue, Apr 25, 2023 at 9:56 AM Thomas Dullien >>> >> >> >> <thomas.dull...@elastic.co> wrote: >>> >> >> >> > >>> >> >> >> > Ah, I see what you mean. >>> >> >> >> > >>> >> >> >> > You are correct -- the change will not speed up a 5-byte >>> word, but it *will* speed up all 8+-byte words, at no cost to the shorter >>> words. >>> >> >> >> > >>> >> >> >> > On Tue, Apr 25, 2023 at 3:20 PM Robert Muir <rcm...@gmail.com> >>> wrote: >>> >> >> >> >> >>> >> >> >> >> if a word is of length 5, processing 8 bytes at a time isn't >>> going to >>> >> >> >> >> speed anything up. there aren't 8 bytes to process. >>> >> >> >> >> >>> >> >> >> >> On Tue, Apr 25, 2023 at 9:17 AM Thomas Dullien >>> >> >> >> >> <thomas.dull...@elastic.co.invalid> wrote: >>> >> >> >> >> > >>> >> >> >> >> > Is average word length <= 4 realistic though? I mean, even >>> the english wiki corpus has ~5, which would require two calls to the lucene >>> layer instead of one; e.g. multiple layers of virtual dispatch that are >>> unnecessary? >>> >> >> >> >> > >>> >> >> >> >> > You're not going to pay any cycles for reading 8 bytes >>> instead of 4 bytes, so the cost of doing so will be the same - while >>> speeding up in cases where 4 isn't quite enough? >>> >> >> >> >> > >>> >> >> >> >> > Cheers, >>> >> >> >> >> > Thomas >>> >> >> >> >> > >>> >> >> >> >> > On Tue, Apr 25, 2023 at 3:07 PM Robert Muir < >>> rcm...@gmail.com> wrote: >>> >> >> >> >> >> >>> >> >> >> >> >> i think from my perspective it has nothing to do with >>> cpus being >>> >> >> >> >> >> 32-bit or 64-bit and more to do with the average length >>> of terms in >>> >> >> >> >> >> most languages being smaller than 8. for the languages >>> with longer >>> >> >> >> >> >> word length, its usually because of complex morphology >>> that most users >>> >> >> >> >> >> would stem away. so doing 4 bytes at a time seems optimal >>> IMO. >>> >> >> >> >> >> languages from nature don't care about your cpu. >>> >> >> >> >> >> >>> >> >> >> >> >> On Tue, Apr 25, 2023 at 8:52 AM Michael McCandless >>> >> >> >> >> >> <luc...@mikemccandless.com> wrote: >>> >> >> >> >> >> > >>> >> >> >> >> >> > For a truly "pure" indexing test I usually use a single >>> thread for indexing, and SerialMergeScheduler (using that single thread to >>> also do single-threaded merging). It makes the indexing take forever lol >>> but it produces "comparable" results. >>> >> >> >> >> >> > >>> >> >> >> >> >> > But ... this sounds like a great change anyway? Do we >>> really need to gate it on benchmark results? Do we think there could be a >>> downside e.g. slower indexing on (the dwindling) 32 bit CPUs? >>> >> >> >> >> >> > >>> >> >> >> >> >> > Mike McCandless >>> >> >> >> >> >> > >>> >> >> >> >> >> > http://blog.mikemccandless.com >>> >> >> >> >> >> > >>> >> >> >> >> >> > >>> >> >> >> >> >> > On Tue, Apr 25, 2023 at 7:39 AM Robert Muir < >>> rcm...@gmail.com> wrote: >>> >> >> >> >> >> >> >>> >> >> >> >> >> >> I think the results of the benchmark will depend on >>> the properties of >>> >> >> >> >> >> >> the indexed terms. For english wikipedia (luceneutil) >>> the average word >>> >> >> >> >> >> >> length is around 5 bytes so this optimization may not >>> do much. >>> >> >> >> >> >> >> >>> >> >> >> >> >> >> On Tue, Apr 25, 2023 at 1:58 AM Patrick Zhai < >>> zhai7...@gmail.com> wrote: >>> >> >> >> >> >> >> > >>> >> >> >> >> >> >> > I did a quick run with your patch, but since I >>> turned on the CMS as well as TieredMergePolicy I'm not sure how fair the >>> comparison is. Here's the result: >>> >> >> >> >> >> >> > Candidate: >>> >> >> >> >> >> >> > Indexer: indexing done (890209 msec); total 33332620 >>> docs >>> >> >> >> >> >> >> > Indexer: waitForMerges done (71622 msec) >>> >> >> >> >> >> >> > Indexer: finished (961877 msec) >>> >> >> >> >> >> >> > Baseline: >>> >> >> >> >> >> >> > Indexer: indexing done (909706 msec); total 33332620 >>> docs >>> >> >> >> >> >> >> > Indexer: waitForMerges done (54775 msec) >>> >> >> >> >> >> >> > Indexer: finished (964528 msec) >>> >> >> >> >> >> >> > >>> >> >> >> >> >> >> > For more accurate comparison I guess it's better to >>> use LogxxMergePolicy and turn off CMS? If you want to run it yourself you >>> can find the lines I quoted from the log file. >>> >> >> >> >> >> >> > >>> >> >> >> >> >> >> > Patrick >>> >> >> >> >> >> >> > >>> >> >> >> >> >> >> > On Mon, Apr 24, 2023 at 12:34 PM Thomas Dullien < >>> thomas.dull...@elastic.co.invalid> wrote: >>> >> >> >> >> >> >> >> >>> >> >> >> >> >> >> >> Hey all, >>> >> >> >> >> >> >> >> >>> >> >> >> >> >> >> >> I've been experimenting with fixing some >>> low-hanging performance fruit in the ElasticSearch codebase, and came >>> across the fact that the MurmurHash implementation that is used by >>> ByteRef.hashCode() is reading 4 bytes per loop iteration (which is likely >>> an artifact from 32-bit architectures, which are ever-less-important). I >>> made a small fix to change the implementation to read 8 bytes per loop >>> iteration; I expected a very small impact (2-3% CPU or so over an indexing >>> run in ElasticSearch), but got a pretty nontrivial throughput improvement >>> over a few indexing benchmarks. >>> >> >> >> >> >> >> >> >>> >> >> >> >> >> >> >> I tried running Lucene-only benchmarks, and >>> succeeded in running the example from >>> https://github.com/mikemccand/luceneutil - but I couldn't figure out >>> how to run indexing benchmarks and how to interpret the results. >>> >> >> >> >> >> >> >> >>> >> >> >> >> >> >> >> Could someone help me in running the benchmarks for >>> the attached patch? >>> >> >> >> >> >> >> >> >>> >> >> >> >> >> >> >> Cheers, >>> >> >> >> >> >> >> >> Thomas >>> >> >> >> >> >> >> >> >>> >> >> >> >> >> >> >> >>> --------------------------------------------------------------------- >>> >> >> >> >> >> >> >> To unsubscribe, e-mail: >>> dev-unsubscr...@lucene.apache.org >>> >> >> >> >> >> >> >> For additional commands, e-mail: >>> dev-h...@lucene.apache.org >>> >> >> >> >> >> >> >>> >> >> >> >> >> >> >>> --------------------------------------------------------------------- >>> >> >> >> >> >> >> To unsubscribe, e-mail: >>> dev-unsubscr...@lucene.apache.org >>> >> >> >> >> >> >> For additional commands, e-mail: >>> dev-h...@lucene.apache.org >>> >> >> >> >> >> >> >>> >> >> >> >> >> >>> >> >> >> >> >> >>> --------------------------------------------------------------------- >>> >> >> >> >> >> To unsubscribe, e-mail: dev-unsubscr...@lucene.apache.org >>> >> >> >> >> >> For additional commands, e-mail: >>> dev-h...@lucene.apache.org >>> >> >> >> >> >> >>> >> <murmur-tests.patch> > --------------------------------------------------------------------- > To unsubscribe, e-mail: dev-unsubscr...@lucene.apache.org > For additional commands, e-mail: dev-h...@lucene.apache.org > > >
