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https://issues.apache.org/jira/browse/LUCENE-10627?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17564086#comment-17564086
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LuYunCheng commented on LUCENE-10627:
-------------------------------------
[~rcmuir] Hi, At latest commit i *reuse ByteBuffersDataInput* to reduce memory
copy because it can get from ByteBuffersDataOutput.toDataInput directly. and it
could reduce the code complexity.
> Using CompositeByteBuf to Reduce Memory Copy
> --------------------------------------------
>
> Key: LUCENE-10627
> URL: https://issues.apache.org/jira/browse/LUCENE-10627
> Project: Lucene - Core
> Issue Type: Improvement
> Components: core/codecs, core/store
> Reporter: LuYunCheng
> Priority: Major
>
> Code: [https://github.com/apache/lucene/pull/987]
> I see When Lucene Do flush and merge store fields, need many memory copies:
> {code:java}
> Lucene Merge Thread #25940]" #906546 daemon prio=5 os_prio=0 cpu=20503.95ms
> elapsed=68.76s tid=0x00007ee990002c50 nid=0x3aac54 runnable
> [0x00007f17718db000]
> java.lang.Thread.State: RUNNABLE
> at
> org.apache.lucene.store.ByteBuffersDataOutput.toArrayCopy(ByteBuffersDataOutput.java:271)
> at
> org.apache.lucene.codecs.compressing.CompressingStoredFieldsWriter.flush(CompressingStoredFieldsWriter.java:239)
> at
> org.apache.lucene.codecs.compressing.CompressingStoredFieldsWriter.finishDocument(CompressingStoredFieldsWriter.java:169)
> at
> org.apache.lucene.codecs.compressing.CompressingStoredFieldsWriter.merge(CompressingStoredFieldsWriter.java:654)
> at
> org.apache.lucene.index.SegmentMerger.mergeFields(SegmentMerger.java:228)
> at org.apache.lucene.index.SegmentMerger.merge(SegmentMerger.java:105)
> at org.apache.lucene.index.IndexWriter.mergeMiddle(IndexWriter.java:4760)
> at org.apache.lucene.index.IndexWriter.merge(IndexWriter.java:4364)
> at
> org.apache.lucene.index.IndexWriter$IndexWriterMergeSource.merge(IndexWriter.java:5923)
> at
> org.apache.lucene.index.ConcurrentMergeScheduler.doMerge(ConcurrentMergeScheduler.java:624)
> at
> org.elasticsearch.index.engine.ElasticsearchConcurrentMergeScheduler.doMerge(ElasticsearchConcurrentMergeScheduler.java:100)
> at
> org.apache.lucene.index.ConcurrentMergeScheduler$MergeThread.run(ConcurrentMergeScheduler.java:682)
> {code}
> When Lucene *CompressingStoredFieldsWriter* do flush documents, it needs many
> memory copies:
> With Lucene90 using {*}LZ4WithPresetDictCompressionMode{*}:
> # bufferedDocs.toArrayCopy copy blocks into one continue content for chunk
> compress
> # compressor copy dict and data into one block buffer
> # do compress
> # copy compressed data out
> With Lucene90 using {*}DeflateWithPresetDictCompressionMode{*}:
> # bufferedDocs.toArrayCopy copy blocks into one continue content for chunk
> compress
> # do compress
> # copy compressed data out
>
> I think we can use -CompositeByteBuf- to reduce temp memory copies:
> # we do not have to *bufferedDocs.toArrayCopy* when just need continues
> content for chunk compress
>
> I write a simple mini benchamrk in test code ([link
> |https://github.com/apache/lucene/blob/5a406a5c483c7fadaf0e8a5f06732c79ad174d11/lucene/core/src/test/org/apache/lucene/codecs/lucene90/compressing/TestCompressingStoredFieldsFormat.java#L353]):
> *LZ4WithPresetDict run* Capacity:41943040(bytes) , iter 10times: Origin
> elapse:5391ms , New elapse:5297ms
> *DeflateWithPresetDict run* Capacity:41943040(bytes), iter 10times: Origin
> elapse:{*}115ms{*}, New elapse:{*}12ms{*}
>
> And I run runStoredFieldsBenchmark with doc_limit=-1:
> shows:
> ||Msec to index||BEST_SPEED ||BEST_COMPRESSION||
> |Baseline|318877.00|606288.00|
> |Candidate|314442.00|604719.00|
>
> -----------UPDATE-----------
>
> I try to *reuse ByteBuffersDataInput* to reduce memory copy because it can
> get from ByteBuffersDataOutput.toDataInput. and it could reduce this
> complexity （[PR|https://github.com/apache/lucene/pull/987]）
> BUT i am not sure whether can change Compressor interface compress input
> param from byte[] to ByteBuffersDataInput. If change this interface
> [like|https://github.com/apache/lucene/blob/382962f22df3ee3af3fb538b877c98d61a622ddb/lucene/core/src/java/org/apache/lucene/codecs/compressing/Compressor.java#L35],
> it increased the backport code
> [like|https://github.com/apache/lucene/blob/382962f22df3ee3af3fb538b877c98d61a622ddb/lucene/core/src/java/org/apache/lucene/codecs/compressing/CompressionMode.java#L274],
> however if we change the interface with ByteBuffersDataInput, we can
> optimize memory copy into different compress algorithm code.
> Also, i found we can do more memory copy reduce in
> *{{{}CompressingStoredFieldsWriter.{}}}{{{}copyOneDoc
> [like|https://github.com/apache/lucene/blob/382962f22df3ee3af3fb538b877c98d61a622ddb/lucene/core/src/java/org/apache/lucene/codecs/lucene90/compressing/Lucene90CompressingStoredFieldsWriter.java#L516]
> and CompressingTermVectorsWriter.flush{}}}*
>
> I think this commit just reduce memory copy, so we not only use one benchmark
> time metric but also use jvm gc time to see the improvement. so i try to add
> StatisticsHelper into
> StoredFieldsBenchmark.([code|https://github.com/luyuncheng/luceneutil/commit/e77c7c7bff01bb036b1826e7ec5d46ad7ed5666d])
> so at latest commit:
> # using ByteBuffersDataInput to reduce memory copy in
> {{CompressingStoredFieldsWriter}} doing {{flush}}
> # using ByteBuffersDataInput to reduce memory copy in
> {{CompressingTermVectorsWriter}} doing {{flush}}
> # using ByteBuffer to *reduce memory copy* in
> *{{CompressingStoredFieldsWriter}} doing {{copyOneDoc}}*
> # replace compressor interface param from byte[] to ByteBuffersDataInput
>
> {{i do the runStoredFieldsBenchmark with jvm StatisticsHelper it shows as
> following:}}
> ||Msec to index||BEST_SPEED ||BEST_SPEED YGC
> ||BEST_COMPRESSION||BEST_COMPRESSION YGC||
> |Baseline|317973|1176 ms (258 collections)|605492|1476 ms (264 collections)|
> |Candidate|314765|1012 ms (238 collections)|601253|1175 ms (234 collections)|
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