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From Erick Erickson <>
Subject Re: Index size and performance degradation
Date Sun, 12 Jun 2011 00:10:06 GMT
<<<We can't assume anything about the machine running it,
so testing won't really tell us much>>>

Hmmm, then it's pretty hopeless I think. Problem is that
anything you say about running on a machine with
2G available memory on a single processor is completely
incomparable to running on a machine with 64G of
memory available for Lucene and 16 processors.

There's really no such thing as an "optimum" Lucene index
size, it always relates to the characteristics of the
underlying hardware.

I think the best you can do is actually test on various
configurations, then at least you can say "on configuration
X this is the tipping point".

Sorry there isn't a better answer that I know of, but...


On Sat, Jun 11, 2011 at 3:37 PM, Itamar Syn-Hershko <> wrote:
> Hi all,
> I know Lucene indexes to be at their optimum up to a certain size - said to
> be around several GBs. I haven't found a good discussion over this, but its
> my understanding that at some point its better to split an index into parts
> (a la sharding) than to continue searching on a huge-size index. I assume
> this has to do with OS and IO configurations. Can anyone point me to more
> info on this?
> We have a product that is using Lucene for various searches, and at the
> moment each type of search is using its own Lucene index. We plan on
> refactoring the way it works and to combine all indexes into one - making
> the whole system more robust and with a smaller memory footprint, among
> other things.
> Assuming the above is true, we are interested in knowing how to do this
> correctly. Initially all our indexes will be run in one big index, but if at
> some index size there is a severe performance degradation we would like to
> handle that correctly by starting a new FSDirectory index to flush into, or
> by re-indexing and moving large indexes into their own Lucene index.
> Are there are any guidelines for measuring or estimating this correctly?
> what we should be aware of while considering all that? We can't assume
> anything about the machine running it, so testing won't really tell us
> much...
> Thanks in advance for any input on this,
> Itamar.
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