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From "Michael McCandless (JIRA)" <>
Subject [jira] Closed: (LUCENE-983) Enable IndexReader to merge tail segments on demand, in RAM, when opening
Date Fri, 17 Aug 2007 21:36:30 GMT


Michael McCandless closed LUCENE-983.

    Resolution: Won't Fix

On further discussion in LUCENE-845 it doesn't look like this idea is worth pursuing...

> Enable IndexReader to merge tail segments on demand, in RAM, when opening
> -------------------------------------------------------------------------
>                 Key: LUCENE-983
>                 URL:
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: Index
>            Reporter: Michael McCandless
>            Assignee: Michael McCandless
>            Priority: Minor
>             Fix For: 2.3
> Spinoff from LUCENE-845.
> In LUCENE-845, the IndexWriter must pay a high cost (O(N^2) merge
> cost) for keeping the number of segments "always small" in the case
> where flushes of very small segments (1 doc as worst case) happen
> frequently.  This happens in "low latency" applications.
> This is because IndexWriter must be ready "at every moment" for an
> IndexReader to open the index.
> But, if we allow IndexReader to use some RAM (give it a RAM buffer) to
> load the long tail of small segments into a RAMDirectory, and then
> merge them (in RAM), this allows IndexReader to still have good
> performance on the index without IndexWriter paying this high merge
> cost.  This effectively allows us to optimize the tail segments "on
> demand" when a reader needs to use them.
> When we combine this with LUCENE-743 (efficient "re-open" of a reader)
> then we should be able to efficiently handle low latency applications.

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