[
http://issues.apache.org/jira/browse/LUCENE-565?page=comments#action_12452039 ]
Ning Li commented on LUCENE-565:
--------------------------------
With the recent commits to IndexWriter, this patch no longer applies cleanly.
The 5 votes for this issue encourages
me to submit yet another patch. :-) But before I do that, I'd like to briefly
describe the design again and welcome all
suggestions that help improve it and help get it committed. :-)
With the new merge policy committed, the change to IndexWriter is minimal:
three zero-or-one-line functions are
added and used.
1 timeToFlushRam(): return true if number of ram segments >= maxBufferedDocs
and used in maybeFlushRamSegments()
2 anythingToFlushRam(): return true if number of ram segments > 0 and used in
flushRamSegments()
3 doAfterFlushRamSegments(): do nothing and called in mergeSegments() if the
merge is on ram segments
The new IndexModifier is a subclass of IndexWriter and only overwrites the
three functions described above.
1 timeToFlushRam(): return true if number of ram segments >= maxBufferedDocs
OR if number of buffered
deletes >= maxBufferedDeletes
2 anythingToFlushRam(): return true if number of ram segments > 0 OR if
number of buffered deletes > 0
3 doAfterFlushRamSegments(): properly flush buffered deletes
The new IndexModifier supports all APIs from the current IndexModifier except
one: deleteDocument(int doc).
I had commented on this before: "I deliberately left that one out. This is
because document ids are changing
as documents are deleted and segments are merged. Users don't know exactly when
segments are merged
thus ids are changed when using IndexModifier."
This behaviour is true for both the new IndexModifier and the current
IndexModifier. If this is preventing this
patch from getting accepted, I'm willing to add this, but I will detail this in
the Java doc so users of this function
are aware of this behaviour.
> Supporting deleteDocuments in IndexWriter (Code and Performance Results
> Provided)
> ---------------------------------------------------------------------------------
>
> Key: LUCENE-565
> URL: http://issues.apache.org/jira/browse/LUCENE-565
> Project: Lucene - Java
> Issue Type: Bug
> Components: Index
> Reporter: Ning Li
> Attachments: IndexWriter.java, IndexWriter.July09.patch,
> IndexWriter.patch, KeepDocCount0Segment.Sept15.patch,
> NewIndexModifier.July09.patch, NewIndexModifier.Sept21.patch,
> NewIndexWriter.Aug23.patch, NewIndexWriter.July18.patch,
> newMergePolicy.Sept08.patch, perf-test-res.JPG, perf-test-res2.JPG,
> perfres.log, TestBufferedDeletesPerf.java, TestWriterDelete.java
>
>
> Today, applications have to open/close an IndexWriter and open/close an
> IndexReader directly or indirectly (via IndexModifier) in order to handle a
> mix of inserts and deletes. This performs well when inserts and deletes
> come in fairly large batches. However, the performance can degrade
> dramatically when inserts and deletes are interleaved in small batches.
> This is because the ramDirectory is flushed to disk whenever an IndexWriter
> is closed, causing a lot of small segments to be created on disk, which
> eventually need to be merged.
> We would like to propose a small API change to eliminate this problem. We
> are aware that this kind change has come up in discusions before. See
> http://www.gossamer-threads.com/lists/lucene/java-dev/23049?search_string=indexwriter%20delete;#23049
> . The difference this time is that we have implemented the change and
> tested its performance, as described below.
> API Changes
> -----------
> We propose adding a "deleteDocuments(Term term)" method to IndexWriter.
> Using this method, inserts and deletes can be interleaved using the same
> IndexWriter.
> Note that, with this change it would be very easy to add another method to
> IndexWriter for updating documents, allowing applications to avoid a
> separate delete and insert to update a document.
> Also note that this change can co-exist with the existing APIs for deleting
> documents using an IndexReader. But if our proposal is accepted, we think
> those APIs should probably be deprecated.
> Coding Changes
> --------------
> Coding changes are localized to IndexWriter. Internally, the new
> deleteDocuments() method works by buffering the terms to be deleted.
> Deletes are deferred until the ramDirectory is flushed to disk, either
> because it becomes full or because the IndexWriter is closed. Using Java
> synchronization, care is taken to ensure that an interleaved sequence of
> inserts and deletes for the same document are properly serialized.
> We have attached a modified version of IndexWriter in Release 1.9.1 with
> these changes. Only a few hundred lines of coding changes are needed. All
> changes are commented by "CHANGE". We have also attached a modified version
> of an example from Chapter 2.2 of Lucene in Action.
> Performance Results
> -------------------
> To test the performance our proposed changes, we ran some experiments using
> the TREC WT 10G dataset. The experiments were run on a dual 2.4 Ghz Intel
> Xeon server running Linux. The disk storage was configured as RAID0 array
> with 5 drives. Before indexes were built, the input documents were parsed
> to remove the HTML from them (i.e., only the text was indexed). This was
> done to minimize the impact of parsing on performance. A simple
> WhitespaceAnalyzer was used during index build.
> We experimented with three workloads:
> - Insert only. 1.6M documents were inserted and the final
> index size was 2.3GB.
> - Insert/delete (big batches). The same documents were
> inserted, but 25% were deleted. 1000 documents were
> deleted for every 4000 inserted.
> - Insert/delete (small batches). In this case, 5 documents
> were deleted for every 20 inserted.
> current current new
> Workload IndexWriter IndexModifier IndexWriter
> -----------------------------------------------------------------------
> Insert only 116 min 119 min 116 min
> Insert/delete (big batches) -- 135 min 125 min
> Insert/delete (small batches) -- 338 min 134 min
> As the experiments show, with the proposed changes, the performance
> improved by 60% when inserts and deletes were interleaved in small batches.
> Regards,
> Ning
> Ning Li
> Search Technologies
> IBM Almaden Research Center
> 650 Harry Road
> San Jose, CA 95120
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