Hi Shai,
absolutely!
we have been there, and there are already some micro benchmarks done in
LUCENE-1345
just do not forget to use -1 < doc instead of -1 != doc, trust me, Yonik
convinced me :)
as a side effect, this change would have some positive effects on iterator
semantics, prevents, very hard to find, "one off" bugs " caused by calling
doc() before calling next()". we had quite a few of those.
-1 is good, as it supports "move to the first" in next() without
if(initialized), just incrementing
.
cheers,
eks
From: Shai Erera <ser...@gmail.com>
To: java-dev@lucene.apache.org
Sent: Friday, 24 April, 2009 21:26:21
Subject: Another possible optimization - now in DocIdSetIterator
Hi
I think we can make some optimization to DocIdSetIterator. Today, it defines
next() and skipTo(int) which return a boolean. I've checked the code and it
looks like almost always when these two are called, they are followed by a call
to doc().
I was thinking that if those two returned the doc Id they are at, instead of
boolean, that will save the call to doc(). Those that use these can:
* Compare doc to a NO_MORE_DOCS constant (set to -1), to understand there are
no more docs in this iterator.
* If skipTo() is called, compare the 'target' to the returned Id, and if they
are not the same, save it so that the next skipTo is requested, they don't
perform it if the returned Id is greater than the target. If it's not possible
to save it, they can call doc() to get that information.
The way I see it, the impls that will still need to call doc() will lose
nothing. All we'll do is change the 'if' from comparing a boolean to comparing
ints (even though that's a bit less efficient than comparing booleans). The
impls that call doc() just because all they have in hand is a boolean, will
gain.
Obviously we can't change those methods' signature, so we can deprecate them
and intorudce nextDoc() and skipToDoc(int target). We should still keep doc()
around though.
What do you think? If you agree to this change, I can add them to 1593, or
create a new issue (I prefer the latter so that 1593 will be focused on the
changes to Collectors).
Shai
