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From Erick Erickson <erickerick...@gmail.com>
Subject Re: how soft-commit works
Date Tue, 17 Sep 2013 12:38:20 GMT
Here's a rather long blog post I wrote up that might help:

http://searchhub.org/2013/08/23/understanding-transaction-logs-softcommit-and-commit-in-sorlcloud/

Best,
Erick


On Mon, Sep 16, 2013 at 1:43 PM, Shawn Heisey <solr@elyograg.org> wrote:

> On 9/16/2013 7:01 AM, Matteo Grolla wrote:
> > Can anyone explain me the following things about soft-commit?
> > -For searches o access new documents I think a new searcher is opened
> after a soft commit.
> >       How does the near realtime requirement for soft commit match with
> the potentially long time taken to warm up caches for the new searcher?
> > -Is it a good idea to set
> >       openSearcher=false in auto commit
> >       and rely on soft auto commit to see new data in searches?
>
> That is a very common way for installs requiring NRT updates to get
> configured.
>
> NRTCachingDirectoryFactory, which is the directory class used in the
> example since 4.0, is a wrapper around MMapDirectoryFactory, which is
> the old default in 3.x.
>
> For soft commits, the NRT directory keeps small commits in RAM rather
> than writing it to the disk, which makes the process of opening a new
> searcher happen a lot faster.
>
>
> http://lucene.apache.org/core/4_4_0/core/org/apache/lucene/store/NRTCachingDirectory.html
>
> If your index rate is very fast or you index large amounts of data, the
> NRT directory doesn't gain you much over MMap, but because we made it
> the default in the example, it probably doesn't have any performance
> detriment.
>
> Thanks,
> Shawn
>
>

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