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From "Michael Busch (JIRA)" <j...@apache.org>
Subject [jira] Commented: (LUCENE-2324) Per thread DocumentsWriters that write their own private segments
Date Tue, 18 Jan 2011 19:32:45 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-2324?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12983346#action_12983346
] 

Michael Busch commented on LUCENE-2324:
---------------------------------------

bq. Why does DW.anyDeletions need to be sync'd?

Hmm good point.  Actually only the call to DW.pendingDeletes.any() needs to be synced, but
not the loop that calls the DWPTs.

{quote}
In ThreadAffinityDWTP... it may be better if we had a single queue,
where threads wait in line, if no DWPT is available? And when a DWPT
finishes it then notifies any waiting threads? (Ie, instead of queue-per-DWPT).
{quote}

Whole foods instead of safeway? :)
Yeah that would be fairer.  A large doc (= a full cart) wouldn't block unlucky other docs.
 I'll make that change, good idea!

{quote}
I see the fieldInfos.update(dwpt.getFieldInfos()) (in
DW.updateDocument) - is there a risk that two threads bring a new
field into existence at the same time, but w/ different config? Eg
one doc omitsTFAP and the other doesn't? Or, on flush, does each DWPT
use its private FieldInfos to correctly flush the segment? (Hmm: do
we seed each DWPT w/ the original FieldInfos created by IW on init?).
{quote}

Every DWPT has its own private FieldInfos.  When a segment is flushed the DWPT uses its private
FI and then it updates the original DW.fieldInfos (from IW), which is a synchronized call.
 

The only consumer of DW.getFieldInfos() is SegmentMerger in IW.  Hmm, given that IW.flush()
isn't synchronized anymore I assume this can lead into a problem?  E.g. the SegmentMerger
gets a FieldInfos that's "newer" than the list of segments it's trying to flush?

bq. How are we handling the case of open IW, do delete-by-term but no added docs?

DW has a SegmentDeletes (pendingDeletes) which gets pushed to the last segment.  We only add
delTerms to DW.pendingDeletes if we couldn't push it to any DWPT.  Btw. I think the whole
pushDeletes business isn't working correctly yet, I'm looking into it.  I need to understand
the code that coalesces the deletes better. 

bq. In DW.deleteTerms... shouldn't we skip a DWPT if it has no buffered docs?

Yeah, I did that already, but not committed yet.

> 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,
lucene-2324.patch, lucene-2324.patch, LUCENE-2324.patch, test.out, test.out, 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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