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https://issues.apache.org/jira/browse/LUCENE-983?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Michael McCandless closed LUCENE-983.
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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: https://issues.apache.org/jira/browse/LUCENE-983
> 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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