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From "Michael McCandless (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-2575) Concurrent byte and int block implementations
Date Thu, 29 Jul 2010 09:38:16 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-2575?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12893564#action_12893564
] 

Michael McCandless commented on LUCENE-2575:
--------------------------------------------

Logically, every term has its own open IndexOutput, where it can write any number of bytes.
 During indexing, when we hit a given term, we init its IndexOutput (two of of them -- one
frq, one prx) and write a few bytes as appropriate.

It's that abstraction that the interleaved byte slices API provides -- the ability to hold
open a great many IndexOutputs.

We should then be able to init IndexInputs against these slices as well, but they can only
sequentially scan.

To handle skipping, I think we can write to another ByteBlockPool?  That skip data would be
similar to the multi-level skip data we now record, except instead of indexing into a single
frq or prx file, it indexes into positions in the primary ByteBlockPool.

Where is there a concurrency problem?  Is it a JMM visibility issue of writes from one thread
vs reads, in a shared byte[]?

> Concurrent byte and int block implementations
> ---------------------------------------------
>
>                 Key: LUCENE-2575
>                 URL: https://issues.apache.org/jira/browse/LUCENE-2575
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: Index
>    Affects Versions: Realtime Branch
>            Reporter: Jason Rutherglen
>             Fix For: Realtime Branch
>
>
> The current *BlockPool implementations aren't quite concurrent.
> We really need something that has a locking flush method, where
> flush is called at the end of adding a document. Once flushed,
> the newly written data would be available to all other reading
> threads (ie, postings etc). I'm not sure I understand the slices
> concept, it seems like it'd be easier to implement a seekable
> random access file like API. One'd seek to a given position,
> then read or write from there. The underlying management of byte
> arrays could then be hidden?

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