As a follow-up, I ran a test using the same parameters as above, only
changing M=200 to M=16. This did result in a single segment in both
cases (9.3, 9.4) and the performance was pretty similar; within noise
I think. The main difference I saw was that the 9.3 index was written
using CFS:
9.4:
recall latency nDoc fanout maxConn beamWidth visited index ms
0.755 1.36 1000000 100 16 100 200 891402 1.00
post-filter
-rw-r--r-- 1 sokolovm amazon 382M Sep 13 13:06
_0_Lucene94HnswVectorsFormat_0.vec
-rw-r--r-- 1 sokolovm amazon 262K Sep 13 13:06
_0_Lucene94HnswVectorsFormat_0.vem
-rw-r--r-- 1 sokolovm amazon 131M Sep 13 13:06
_0_Lucene94HnswVectorsFormat_0.vex
9.3:
recall latency nDoc fanout maxConn beamWidth visited index ms
0.775 1.34 1000000 100 16 100 4033 977043
rw-r--r-- 1 sokolovm amazon 297 Sep 13 13:26 _0.cfe
-rw-r--r-- 1 sokolovm amazon 516M Sep 13 13:26 _0.cfs
-rw-r--r-- 1 sokolovm amazon 340 Sep 13 13:26 _0.si
On Tue, Sep 13, 2022 at 8:50 AM Michael Sokolov <msoko...@gmail.com> wrote:
>
> I ran another test. I thought I had increased the RAM buffer size to
> 8G and heap to 16G. However I still see two segments in the index that
> was created. And looking at the infostream I see:
>
> dir=MMapDirectory@/local/home/sokolovm/workspace/knn-perf/glove-100-angular.hdf5-train-200-200.index
> lockFactory=org\
> .apache.lucene.store.NativeFSLockFactory@4466af20
> index=
> version=9.4.0
> analyzer=org.apache.lucene.analysis.standard.StandardAnalyzer
> ramBufferSizeMB=8000.0
> maxBufferedDocs=-1
> ...
> perThreadHardLimitMB=1945
> ...
> DWPT 0 [2022-09-13T02:42:53.329404950Z; main]: flush postings as
> segment _6 numDocs=555373
> IW 0 [2022-09-13T02:42:53.330671171Z; main]: 0 msec to write norms
> IW 0 [2022-09-13T02:42:53.331113184Z; main]: 0 msec to write docValues
> IW 0 [2022-09-13T02:42:53.331320146Z; main]: 0 msec to write points
> IW 0 [2022-09-13T02:42:56.424195657Z; main]: 3092 msec to write vectors
> IW 0 [2022-09-13T02:42:56.429239944Z; main]: 4 msec to finish stored fields
> IW 0 [2022-09-13T02:42:56.429593512Z; main]: 0 msec to write postings
> and finish vectors
> IW 0 [2022-09-13T02:42:56.430309031Z; main]: 0 msec to write fieldInfos
> DWPT 0 [2022-09-13T02:42:56.431721622Z; main]: new segment has 0 deleted docs
> DWPT 0 [2022-09-13T02:42:56.431921144Z; main]: new segment has 0
> soft-deleted docs
> DWPT 0 [2022-09-13T02:42:56.435738086Z; main]: new segment has no
> vectors; no norms; no docValues; no prox; freqs
> DWPT 0 [2022-09-13T02:42:56.435952356Z; main]:
> flushedFiles=[_6_Lucene94HnswVectorsFormat_0.vec, _6.fdm, _6.fdt, _6_\
> Lucene94HnswVectorsFormat_0.vem, _6.fnm, _6.fdx,
> _6_Lucene94HnswVectorsFormat_0.vex]
> DWPT 0 [2022-09-13T02:42:56.436121861Z; main]: flushed codec=Lucene94
> DWPT 0 [2022-09-13T02:42:56.437691468Z; main]: flushed: segment=_6
> ramUsed=1,945.002 MB newFlushedSize=1,065.701 MB \
> docs/MB=521.134
>
> so I think it's this perThreadHardLimit that is triggering the
> flushes? TBH this isn't something I had seen before; but the docs say:
>
> /**
> * Expert: Sets the maximum memory consumption per thread triggering
> a forced flush if exceeded. A
> * {@link DocumentsWriterPerThread} is forcefully flushed once it
> exceeds this limit even if the
> * {@link #getRAMBufferSizeMB()} has not been exceeded. This is a
> safety limit to prevent a {@link
> * DocumentsWriterPerThread} from address space exhaustion due to
> its internal 32 bit signed
> * integer based memory addressing. The given value must be less
> that 2GB (2048MB)
> *
> * @see #DEFAULT_RAM_PER_THREAD_HARD_LIMIT_MB
> */
>
> On Mon, Sep 12, 2022 at 6:28 PM Michael Sokolov <msoko...@gmail.com> wrote:
> >
> > Hi Mayya, thanks for persisting - I think we need to wrestle this to
> > the ground for sure. In the test I ran, RAM buffer was the default
> > checked in, which is weirdly: 1994MB. I did not specifically set heap
> > size. I used maxConn/M=200. I'll try with larger buffer to see if I
> > can get 9.4 to produce a single segment for the same test settings. I
> > see you used a much smaller M (16), which should have produced quite
> > small graphs, and I agree, should have been a single segment. Were you
> > able to verify the number of segments?
> >
> > Agree that decrease in recall is not expected when more segments are
> > produced.
> >
> > On Mon, Sep 12, 2022 at 1:51 PM Mayya Sharipova
> > <mayya.sharip...@elastic.co.invalid> wrote:
> > >
> > > Hello Michael,
> > > Thanks for checking.
> > > Sorry for bringing this up again.
> > > First of all, I am ok with proceeding with the Lucene 9.4 release and
> > > leaving the performance investigations for later.
> > >
> > > I am interested in what's the maxConn/M value you used for your tests?
> > > What was the heap memory and the size of the RAM buffer for indexing?
> > > Usually, when we have multiple segments, recall should increase, not
> > > decrease. But I agree that with multiple segments we can see a big drop
> > > in QPS.
> > >
> > > Here is my investigation with detailed output of the performance
> > > difference between 9.3 and 9.4 releases. In my tests I used a large
> > > indexing buffer (2Gb) and large heap (5Gb) to end up with a single
> > > segment for both 9.3 and 9.4 tests, but still see a big drop in QPS in
> > > 9.4.
> > >
> > > Thank you.
> > >
> > >
> > >
> > >
> > >
> > > On Fri, Sep 9, 2022 at 12:21 PM Alan Woodward <romseyg...@gmail.com>
> > > wrote:
> > >>
> > >> Done. Thanks!
> > >>
> > >> > On 9 Sep 2022, at 16:32, Michael Sokolov <msoko...@gmail.com> wrote:
> > >> >
> > >> > Hi Alan - I checked out the interval queries patch; seems pretty safe,
> > >> > please go ahead and port to 9.4. Thanks!
> > >> >
> > >> > Mike
> > >> >
> > >> > On Fri, Sep 9, 2022 at 10:41 AM Alan Woodward <romseyg...@gmail.com>
> > >> > wrote:
> > >> >>
> > >> >> Hi Mike,
> > >> >>
> > >> >> I’ve opened https://github.com/apache/lucene/pull/11760 as a small
> > >> >> bug fix PR for a problem with interval queries. Am I OK to port this
> > >> >> to the 9.4 branch?
> > >> >>
> > >> >> Thanks, Alan
> > >> >>
> > >> >> On 2 Sep 2022, at 20:42, Michael Sokolov <msoko...@gmail.com> wrote:
> > >> >>
> > >> >> NOTICE:
> > >> >>
> > >> >> Branch branch_9_4 has been cut and versions updated to 9.5 on stable
> > >> >> branch.
> > >> >>
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> > >> >>
> > >> >> * No new features may be committed to the branch.
> > >> >> * Documentation patches, build patches and serious bug fixes may be
> > >> >> committed to the branch. However, you should submit all patches you
> > >> >> want to commit to Jira first to give others the chance to review
> > >> >> and possibly vote against the patch. Keep in mind that it is our
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