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From Erick Erickson <>
Subject Re: memory cost in forceMerge(1)
Date Tue, 11 Aug 2015 04:30:38 GMT
It is generally unnecessary to use forceMerge, that's a legacy from
older versions of Lucene/Solr.
Especially if the index is constantly changing, forceMerge generally
is both expensive and not
very useful.

These indexes must be huge though if any of them are taking 8 hours.
What's the background here?


On Mon, Aug 10, 2015 at 6:28 PM, 丁儒 <> wrote:
> GreetingsNow, i'm using lucene , the version is 4.10.3. For some reason, i called forceMerge(1)
in the end,and the final  space of the Index Library is 15 GB. . But i found that forceMerge(1)
cost a lot of time, and on different machines ,the time differs.  Is this caused by the different
size of memory of the macheines. One has 24GB memory, the other has 48GB memory. And the machine
with 24 GB memory cost nearly 18 hours in forceMerge(1), and the machine with 48 GB memory
cost nearly 8 hours in forceMerge(1). I guess the forceMerge(1) needs too much memory, so
it costs more time in less memory machine. Am i right ?
>     Also, can forceMerge(1)  speed up the search?
> Thank you
> All

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