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https://issues.apache.org/jira/browse/LUCENE-4039?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13269604#comment-13269604
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Shai Erera commented on LUCENE-4039:
------------------------------------
I ran a small benchmark over an index with 1M documents, that was generated
using that .alg file:
{code}
writer.version=LUCENE_40
ram.flush.mb=128
analyzer=org.apache.lucene.analysis.core.WhitespaceAnalyzer
directory=FSDirectory
work.dir=input
doc.stored=false
doc.tokenized=true
doc.term.vector=false
log.step=20000
content.source=org.apache.lucene.benchmark.byTask.feeds.SingleDocSource
task.max.depth.log=2
# ----------------------------------------------------------------------------
ResetSystemErase
CreateIndex
[ { "AddDocs" AddDoc > : 125000 ] : 8
CloseIndex
RepSumByName
{code}
Then I ran the following addIndexes.alg file
{code}
writer.version=LUCENE_40
analyzer=org.apache.lucene.analysis.standard.StandardAnalyzer
directory=FSDirectory
work.dir=output
task.max.depth.log=2
# directory to add to the target index
addindexes.input.dir=input/index
# -----------------------------------------------------------------------
# call addIndexes (Directory)
ResetSystemErase
CreateIndex
{ "AddIndexesDirectory" AddIndexes(true) >
CloseIndex
# call addIndexes (IndexReader)
ResetSystemErase
CreateIndex
{ "AddIndexesReader" AddIndexes(false) >
CloseIndex
RepSumByPref AddIndexes
{code}
The run reports:
{code}
------------> Report Sum By Prefix (AddIndexes) (2 about 2 out of 7)
Operation round runCnt recsPerRun rec/s elapsedSec
avgUsedMem avgTotalMem
AddIndexesDirectory 0 1 1 1.33 0.75
3,873,528 4,194,304
AddIndexesReader 0 1 1 0.06 17.82
5,795,936 7,906,304
{code}
To highlight, the addIndexes(Directory) version is x23 faster than
addIndexes(IndexReader), and that's on a fairly small and simple index (376 MB,
not so many posting lists). That means that on a more complex index, with more
posting lists, more CPU encoding/decoding work will happen, while I suspect the
raw file-system file copies done in addIndexes(Dir) will not be affected much.
This shows how important it is to use addIndexes(Dir) whenever possible ...
> Add AddIndexesTask to Benchmark
> -------------------------------
>
> Key: LUCENE-4039
> URL: https://issues.apache.org/jira/browse/LUCENE-4039
> Project: Lucene - Java
> Issue Type: New Feature
> Components: modules/benchmark
> Reporter: Shai Erera
> Assignee: Shai Erera
> Priority: Minor
> Fix For: 4.0
>
> Attachments: LUCENE-4039.patch
>
>
> I was interested in measuring the performance of
> IndexWriter.addIndexes(Directory) vs. IndexWriter.addIndexes(IndexReader). I
> wrote an AddIndexesTask and a matching .alg. The task takes a parameter
> whether to use the IndexReader or Directory variants. I'll upload the patch
> and describe the perf results.
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