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From Michael McCandless <luc...@mikemccandless.com>
Subject Re: Swapping between indexes
Date Thu, 06 Mar 2008 13:17:09 GMT

Sridhar Raman wrote:

>> This way no reader will ever see the changes until you successfully
>> close the writer.  If the machine crashes the index is still in the
>> starting state as of when the writer was first opened.
> Ok, I have a slight doubt in this.  Say I have gone ahead with  
> Approach 1
> If I have opened the writer with autoCommit=false, and the system  
> crashes,
> does it mean that the changes made to IdxSrch are lost?  If that is  
> the
> case, that might be a problem.  What I actually want is something like
> this.  When the system crashes in between, the search continues to  
> happen on
> the index at T0.  But the updates that were done since T0 also  
> needs to be
> preserved.  Would that happen if I set autoCommit to false?
>
> I realise that I want the cake and eat it too.  But that's the  
> problem we
> face if we keep just a single copy of the index.

Alas, you are right: all changes not committed are lost.  Ie on  
coming back
up after the crash, you would have to re-index everything again.

Lucene is actually not that far from doing what you're asking for  
here.  I think
the only thing missing is the ability to open a reader on a prior  
commit, rather
than the latest one.  If we added that then you could make a custom  
deletion
policy that'd keep your T0 commit, as well as commits being done by your
writer, and only remove them when you decide to switch your readers  
to the
current commit.

But, realize that even with such a change to Lucene, you would still  
lose
everything since the last commit, when the machine crashes.

Mike

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