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https://issues.apache.org/jira/browse/LUCENE-2324?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12979229#action_12979229
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Jason Rutherglen commented on LUCENE-2324:
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{quote}the "flush the world" case? (Ie the app calls IW.commit or
IW.getReader). In this case the thread just one by one pulls all DWPTs that
have any indexed docs out of production, flushes them, clears them, and returns
them to production?{quote}
The 2 cases are: A) Flush every DWPT sequentually (aka flush the world) and
B) flush by RAM usage when adding docs or deleting. A is clear! I think with B
we're saying even if the calling thread is bound to DWPT #1, if DWPT #2 is
greater in size and the aggregate RAM usage exceeds the max, using the calling
thread, we take DWPT #2 out of production, flush, and return it?
{quote}The behavior of calling IW.close while other threads are still adding
docs has never been defined (and, shouldn't be) except that we won't corrupt
your index, and we'll get all docs indexed before .close was called, committed.
So I think even for this case we don't need a global lock.{quote}
Great, that simplifies and clarifies that we do not require a global lock.
{quote}But, you're right: maybe we should sometimes "prune" DWPTs. Or simply
stop recycling any RAM, so that a just-flushed DWPT is an empty shell.{quote}
I'm not sure how we'd prune, typically object pools have a separate eviction
thread, I think that's going overboard? Maybe we can simply throw out the DWPT
and put recycling byte[]s and/or pooling DWPTs back in later if it's necessary?
> Per thread DocumentsWriters that write their own private segments
> -----------------------------------------------------------------
>
> Key: LUCENE-2324
> URL: https://issues.apache.org/jira/browse/LUCENE-2324
> Project: Lucene - Java
> Issue Type: Improvement
> Components: Index
> Reporter: Michael Busch
> Assignee: Michael Busch
> Priority: Minor
> Fix For: Realtime Branch
>
> Attachments: LUCENE-2324-SMALL.patch, LUCENE-2324-SMALL.patch,
> LUCENE-2324-SMALL.patch, LUCENE-2324-SMALL.patch, LUCENE-2324-SMALL.patch,
> lucene-2324.patch, lucene-2324.patch, LUCENE-2324.patch, test.out, test.out
>
>
> See LUCENE-2293 for motivation and more details.
> I'm copying here Mike's summary he posted on 2293:
> Change the approach for how we buffer in RAM to a more isolated
> approach, whereby IW has N fully independent RAM segments
> in-process and when a doc needs to be indexed it's added to one of
> them. Each segment would also write its own doc stores and
> "normal" segment merging (not the inefficient merge we now do on
> flush) would merge them. This should be a good simplification in
> the chain (eg maybe we can remove the *PerThread classes). The
> segments can flush independently, letting us make much better
> concurrent use of IO & CPU.
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