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From Chris Hostetter <hossman_luc...@fucit.org>
Subject Re: index architectures
Date Wed, 18 Oct 2006 14:40:06 GMT

: I *think* that if you reduce your result set by, say, a filter, you might
: drastically reduce what gets sorted. I'm thinking of something like this
: BooleanQuery bq = new BooleanQuery();
: bq.add(Filter for the last N days wrapped in a ConstantScoreQuery, MUST)
: bq.add(all the rest of your stuff).
	...
: Again, I'm note entirely sure when the filter gets applied, before or after
: the sort. Nor am I sure how to tell. I'd sure like you to do the work and

The memory required for sorting on a field is independent of the size of
the result -- so a Filter wouldn't help you here.  The reason is becuase
Sorting builds/uses the FieldCache which cotnains all the values for all
docs, so that it can be reused for Sorting future queries as well.

That said: if you are seeing OOM errors when you sort by a field (but
not when you use the docId ordering, or sort by score) then it sounds like
you are keeping refrences to IndexReaders arround after you've stoped
using them -- the FieldCache is kept in a WeakHashMap keyed off of hte
IndexReader, so it should get garbage collected as soon sa you let go of
it.  Another possibility is that you are sorting on too many fields for it
to be able to build the FieldCache for all of them in the RAM you have
available.

There was some discussion recently on java-dev about an approach to
scoring that took advantage of Lazy Field loading insitead of the
FieldCache to sort on the *stored* value of a field, the goal being to
make sorting small result sets possible with small amount of RAM ... but i
don't remember if the person working on it ever submitted a patch.





-Hoss


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