The regular TermsEnum is really designed for walking terms in linear order. it does have some ability to seek/leapfrog. But this means paths in a query automaton that match no terms result in a wasted seek and cpu, because the api is designed to return the next term after regardless.
On the other hand the intersect() is for intersecting two automata: query and index. Presumably it can also remove more inefficiencies than just the wasted seeks for complex wildcards and fuzzies and stuff, since it can "see" the whole input as an automaton. so for example it might be able to work on blocks of terms at a time and so on. On Mon, Apr 1, 2019, 12:17 PM Stamatis Zampetakis <zabe...@gmail.com> wrote: > Yes it is used. > > I think there are simpler and possibly more efficient ways to implement a > TermRangeQuery and that is why I am looking into this. > But I am also curious to understand what IntersectTermsEnum is supposed to > do. > > Στις Δευ, 1 Απρ 2019 στις 5:34 μ.μ., ο/η Robert Muir <rcm...@gmail.com> > έγραψε: > > > Is this IntersectTermsEnum really being used for term range query? Seems > > like using a standard TermsEnum, seeking to the start of the range, then > > calling next until the end would be easier. > > > > On Mon, Apr 1, 2019, 10:05 AM Stamatis Zampetakis <zabe...@gmail.com> > > wrote: > > > > > Hi all, > > > > > > I am currently working on improving the performance of range queries on > > > strings. I've noticed that using TermRangeQuery with low-selective > > queries > > > is a very bad idea in terms of performance but I cannot clearly explain > > why > > > since it seems related with how the IntersectTermsEnum#next method is > > > implemented. > > > > > > The Javadoc of the class says that the terms index (the burst-trie > > > datastructure) is not used by this implementation of TermsEnum. > However, > > > when I see the implementation of the next method I get the impression > > that > > > this is not accurate. Aren't we using the trie structure to skip parts > of > > > the data when the automaton states do not match? > > > > > > Can somebody provide a high-level intutition of what > > > IntersectTermsEnum#next does? Initially, I thought that it is > traversing > > > the whole trie structure (skipping some branches when necessary) but I > > may > > > be wrong. > > > > > > Thanks in advance, > > > Stamatis > > > > > >
