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From Michael McCandless <luc...@mikemccandless.com>
Subject Re: Sequence IDs for NRT deletes
Date Tue, 20 Jul 2010 19:17:40 GMT
On Tue, Jul 20, 2010 at 1:44 PM, Jason Rutherglen
<jason.rutherglen@gmail.com> wrote:
>> Breaking up RT patches into baby steps would be great :)
>> Actually is the RT branch active (I haven't seen commits going
>> in).
>
> From what we discussed, my impression is that the RT changes
> will be substantial and the sequence ids seem to be something
> that can be implemented now in trunk, then at least a small
> piece of RT would be implemented and tested. A small isolated
> improvement.

I agree.

>> The biggest downside of sequence IDs is increase RAM usage
>> right?
>
> Yes, however the garbage collection would decrease.

Right, much less GC if app frequently reopens.  But a 32X increase in
RAM usage is not trivial; I think we shouldn't enable it by default?

> We should make seq id deletes pluggable.

+1 -- make the deletes impl pluggable (ie one impl is sequence IDs;
another is BitVector).

>> Then, checking if a doc is deleted becomes an int compare
>> instead of a bit lookup, right?
>
> Right it'd be an int compare, I think this'd be ok?

Yeah maybe even more than OK; could be this is faster than looking up
a bit!  (Though it's much more traffic on the memory bus).  Apps may
want to use this even outside of NRT.  Have you tested?

Mike

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