Hey all,
apologies if the chart is incorrect. Anyhow, I think the more important
questions are:
1) Which benchmarks does the Lucene community have that y'all would like to
see an improvement on before accepting this (or any other future)
performance patches?
I'm guessing the reason why the patch improves http_log performance is
because that benchmark indexes many IP addresses, which tend to be 9-15
bytes in length. That does not strike me as an atypical workload.
I've also done some quick experiments to estimate the average UTF-8 word
size of languages in non-ASCII scripts (for example Hindi), and it seems to
me the average word size is 2-3 times larger than english because most
indic characters will encode to 2-3 bytes. The following excerpt from Hindi
Wikipedia is 2242 bytes, but just 146 words
==== begin hindi-example.txt ====
१० वीं शताब्दी के बाद घुमन्तु मुस्लिम वंशों ने जातियता तथा धर्म द्वारा
संघठित तेज घोड़ों से युक्त बड़ी सेना के द्वारा उत्तर-पश्चिमी मैदानों पर बार
बार आकर्मण किया, अंततः १२०६ [[दिल्ली सल्तनत|इस्लामीक दिल्ली सल्तनत]] की
स्थापना हुई।{{sfn|Ludden|2002|p = 68}} उन्हें उतर भारत को
धिक नियंत्रित करना था तथा दक्षिण भारत पर आकर्मण करना था। भारतीय कुलीन वर्ग
के विघटनकारी सल्तनत ने बड़े पैमाने पर गैर-मुस्लिमों को स्वयं के रीतिरिवाजों
पर छोड़ दिया।{{sfn|Asher|Talbot|2008|p = 47}}{{sfn|Metcalf|Metcalf|2006|p =
6}} १३ वीं शताब्दी में [[मंगोल साम्राज्
य|मंगोलों]] द्वारा किये के विनाशकारी आकर्मण से भारत की रक्षा की। सल्तनत के
पतन के कारण स्वशासित [[विजयनगर साम्राज्य|विजयनगर साम्राज्य]] का मार्ग
प्रशस्त हुआ।{{sfn|Asher|Talbot|2008|p = 53}} एक मजबूत [[शैव|शैव परंपरा]] और
सल्तनत की सैन्य तकनीक पर निर्माण करते हुए साम्रा
ज्य ने भारत के विशाल भाग पर शासन किया और इसके बाद लंबे समय तक दक्षिण भारतीय
समाज को प्रभावित किया।{{sfn|Metcalf|Metcalf|2006|p =
12}}{{sfn|Asher|Talbot|2008|p = 53}}
==== end hindi-example.txt ====
cat hindi-example.txt | wc -w
146
2242 divided by 146 yields a word length of ~15 bytes, so I'd be surprised
if average word length of Hindi wikipedia was below 12 bytes.
Do y'all wish for me to create another benchmark for indexing indic scripts
and large corpora of IPv4 and IPv6 addresses (both things that seem not
very niche), and if the patch shows improvement there, will y'all accept it?
2) It'd be great if there was some public documentation about "what we want
to see from a performance improvement before we accept it". I personally
find the discussion around this patch to be bewilderingly long, and I am
happy to help work on such a guideline with others -- IMO having a clear
set of hurdles is preferable to the back-and-forth we've had so far?
Cheers,
Thomas
On Fri, Aug 25, 2023 at 3:38 PM Robert Muir <rcm...@gmail.com> wrote:
> chart is wrong, average word length for english is like 5.
>
> On Fri, Aug 25, 2023 at 9:35 AM Thomas Dullien
> <thomas.dull...@elastic.co.invalid> wrote:
> >
> > Hey all,
> >
> > another data point: There's a diagram with the relevant distributions of
> word lengths in various languages here:
> >
> >
> https://www.reddit.com/r/languagelearning/comments/h9eao2/average_word_length_of_languages_in_europe_except/
> >
> > While English is close to the 8-byte limit, average word length in
> German is 11+ bytes, and Mongolian and Finnish will likewise be 11+ bytes.
> I'll gather some averages over the various Wikipedia indices.
> >
> > Cheers,
> > Thomas
> >
> > On Thu, Aug 24, 2023 at 2:09 PM Thomas Dullien <
> thomas.dull...@elastic.co> wrote:
> >>
> >> 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
> >>>>> >> >> >> >> >> >> >>
> >>>>> >> >> >> >> >> >> >>
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> >>>>> >> >> >> >> >> >>
> >>>>> >> >> >> >> >> >>
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> >>>>> >> >> >> >> >>
> >>>>> >> >> >> >> >>
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> >>>
> >>> <murmur-tests.patch>
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