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From "Ning Li (JIRA)" <>
Subject [jira] Updated: (LUCENE-565) Supporting deleteDocuments in IndexWriter (Code and Performance Results Provided)
Date Mon, 10 Jul 2006 03:39:30 GMT
     [ ]

Ning Li updated LUCENE-565:

    Attachment: IndexWriter.July09.patch

Hi Otis,

I've attached two patch files:
  - IndexWriter.July09.patch is an updated version of the old patch.
  - NewIndexModifier.July09.patch makes minimal changes to IndexWriter and puts new functionalities
in a new class called NewIndexModifier. I didn't name it IndexModifier because the two are
unrelated and I don't want a diff of the two.

All unit test succeeded except the following one:
    [junit] Testcase: testIndex(org.apache.lucene.index.TestIndexModifier):	FAILED
    [junit] expected:<3> but was:<4>
    [junit] junit.framework.AssertionFailedError: expected:<3> but was:<4>
    [junit] 	at org.apache.lucene.index.TestIndexModifier.testIndex(

However, the unit test has a problem, not the patch: IndexWriter's docCount() does not tell
the actual number of documents in an index, only IndexReader's numDocs() does. For example,
in a similar test below, where 10 documents are added, then 1 deleted, then 2 added, the last
call to docCount() returns 12, not 11, with or without the patch.

  public void testIndexSimple() throws IOException {
    Directory ramDir = new RAMDirectory();
    IndexModifier i = new IndexModifier(ramDir, new StandardAnalyzer(), true);
    // add 10 documents initially
    for (int count = 0; count < 10; count++) {
    assertEquals(10, i.docCount());
    assertEquals(9, i.docCount());
    assertEquals(12, i.docCount());

The reason for the docCount() difference in the unit test (which does not affect the correctness
of the patch) is that flushRamSegments() in the patch merges all and only the segments in
ram and write to disk, whereas the original flushRamSegments() merges not only the segments
in ram but *sometimes* also one segment from disk (see in that function the comment "// add
one FS segment?").


> Supporting deleteDocuments in IndexWriter (Code and Performance Results Provided)
> ---------------------------------------------------------------------------------
>          Key: LUCENE-565
>          URL:
>      Project: Lucene - Java
>         Type: Bug

>   Components: Index
>     Reporter: Ning Li
>  Attachments: IndexWriter.July09.patch,, IndexWriter.patch, NewIndexModifier.July09.patch,
> 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
> . 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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