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From robert engels <reng...@ix.netcom.com>
Subject Re: [jira] Commented: (LUCENE-565) Supporting deleteDocuments in IndexWriter (Code and Performance Results Provided)
Date Thu, 06 Jul 2006 22:08:19 GMT
I think I finally see how this is supposed to optimize - basically  
because it remember the terms, and then does the batch deletions.

We avoid all of this messiness by just making sure each document has  
a primary key and we always remove/update by primary key and we can  
keep the operations in an ordered list (actually set since the keys  
are unique, and that way multiple updates to the same document in a  
batch can be coalesced).

I guess still don't see why the change is so involved though...

I would just maintain an ordered list of operations (deletes an adds)  
on the "buffered writer".
When the "buffered" writer is closed:
Create a RamDirectory.
Perform all deletions in a batch on the main IndexReader.
Perform ordered deletes and adds on the RamDirectory.
Merge the RamDirectory with the main index.

This could all be encapsulated in a BufferedIndexWriter class.


On Jul 6, 2006, at 4:34 PM, robert engels wrote:

> I guess I don't see the difference...
>
> You need the write lock to use the indexWriter, and you also need  
> the write lock to perform a deletion, so if you just get the write  
> lock you can perform the deletion and the add, then close the writer.
>
> I have asked how this submission optimizes anything, and I still  
> can't seem to get an answer?
>
>
> On Jul 6, 2006, at 4:27 PM, Otis Gospodnetic wrote:
>
>> I think that patch is for a different scenario, the one where you  
>> can't wait to batch deletes and adds, and want/need to execute  
>> them more frequently and in order they really are happening,  
>> without grouping them.
>>
>> Otis
>>
>> ----- Original Message ----
>> From: robert engels <rengels@ix.netcom.com>
>> To: java-dev@lucene.apache.org
>> Sent: Thursday, July 6, 2006 3:24:13 PM
>> Subject: Re: [jira] Commented: (LUCENE-565) Supporting  
>> deleteDocuments in IndexWriter (Code and Performance Results  
>> Provided)
>>
>> I guess we just chose a much simpler way to do this...
>>
>> Even with you code changes, to see the modification made using the
>> IndexWriter, it must be closed, and a new IndexReader opened.
>>
>> So a far simpler way is to get the collection of updates first, then
>>
>> using opened indexreader,
>> for each doc in collection
>>        delete document using "key"
>> endfor
>>
>> open indexwriter
>> for each doc in collection
>>        add document
>> endfor
>>
>> open indexreader
>>
>>
>> I don't see how your way is any faster. You must always flush to disk
>> and open the indexreader to see the changes.
>>
>>
>>
>> On Jul 6, 2006, at 2:07 PM, Ning Li wrote:
>>
>>> Hi Otis and Robert,
>>>
>>> I added an overview of my changes in JIRA. Hope that helps.
>>>
>>>> Anyway, my test did exercise the small batches, in that in our
>>>> incremental updates we delete the documents with the unique  
>>>> term, and
>>>> then add the new (which is what I assumed this was improving),  
>>>> and I
>>>> saw o appreciable difference.
>>>
>>> Robert, could you describe a bit more how your test is set up? Or a
>>> short
>>> code snippet will help me explain.
>>>
>>> Without the patch, when inserts and deletes are interleaved in small
>>> batches, the performance can degrade dramatically because the
>>> ramDirectory
>>> is flushed to disk whenever an IndexWriter is closed, causing a  
>>> lot of
>>> small segments to be created on disk, which eventually need to be
>>> merged.
>>>
>>> Is this how your test is set up? And, what are the maxBufferedDocs
>>> and the
>>> maxBufferedDeleteTerms in your test? You won't see a performance
>>> improvement
>>> if they are about the same as the small batch size. The patch  
>>> works by
>>> internally buffering inserts and deletes into larger batches.
>>>
>>> Regards,
>>> Ning
>>>
>>>
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>>
>>
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>>
>>
>>
>>
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>


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