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From "Michael McCandless (JIRA)" <j...@apache.org>
Subject [jira] Updated: (LUCENE-2329) Use parallel arrays instead of PostingList objects
Date Thu, 01 Apr 2010 23:50:27 GMT

     [ https://issues.apache.org/jira/browse/LUCENE-2329?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Michael McCandless updated LUCENE-2329:
---------------------------------------

    Attachment: LUCENE-2329.patch

New patch attached:

  * Does away with separate tracking of used vs alloc, in IndexWriter.
    This distinction added much complexity and only saved a small
    number of free/alloc's per flush cycle, especially now that
    postings realloc only in big chunks (parallel arrays).

  * Fixed some over-counting of bytes used.

The indexing throughput is basically unchanged after this (on first
10M 1KB Wikipedia docs), so I think this is a good simplification.


> Use parallel arrays instead of PostingList objects
> --------------------------------------------------
>
>                 Key: LUCENE-2329
>                 URL: https://issues.apache.org/jira/browse/LUCENE-2329
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: Index
>            Reporter: Michael Busch
>            Assignee: Michael Busch
>            Priority: Minor
>             Fix For: 3.1
>
>         Attachments: lucene-2329-2.patch, LUCENE-2329.patch, LUCENE-2329.patch, lucene-2329.patch,
lucene-2329.patch, lucene-2329.patch
>
>
> This is Mike's idea that was discussed in LUCENE-2293 and LUCENE-2324.
> In order to avoid having very many long-living PostingList objects in TermsHashPerField
we want to switch to parallel arrays.  The termsHash will simply be a int[] which maps each
term to dense termIDs.
> All data that the PostingList classes currently hold will then we placed in parallel
arrays, where the termID is the index into the arrays.  This will avoid the need for object
pooling, will remove the overhead of object initialization and garbage collection.  Especially
garbage collection should benefit significantly when the JVM runs out of memory, because in
such a situation the gc mark times can get very long if there is a big number of long-living
objects in memory.
> Another benefit could be to build more efficient TermVectors.  We could avoid the need
of having to store the term string per document in the TermVector.  Instead we could just
store the segment-wide termIDs.  This would reduce the size and also make it easier to implement
efficient algorithms that use TermVectors, because no term mapping across documents in a segment
would be necessary.  Though this improvement we can make with a separate jira issue.

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