Affects Version/s: None
Fix Version/s: None
When a node is close to the root, or it has many outgoing arcs, the FST writes the arcs as an array (each arc gets N bytes), so we can e.g. bin search on lookup.
The problem is N is set to the max(numBytesPerArc), so if you have an outlier arc e.g. with a big output, you can waste many bytes for all the other arcs that didn't need so many bytes.
I generated Kuromoji's FST and found it has 271187 wasted bytes vs total size 1535612 = ~18% wasted.
It would be nice to reduce this.
One thing we could do without packing is: in addNode, if we detect that number of wasted bytes is above some threshold, then don't do the expansion.
Another thing, if we are packing: we could record stats in the first pass about which nodes wasted the most, and then in the second pass (paack) we could set the threshold based on the top X% nodes that waste ...
Another idea is maybe to deref large outputs, so that the numBytesPerArc is more uniform ...