Previously term entries were encoded pairwise (field/term), so
you'd have data like:
F1/T1 F1/T2 F1/T3 F2/T4 F3/T5
As you can see, even though field 1 has 3 terms, we repeat the F1
part in the encoded data. This is a bit wasteful.
In the new format we encode it as a list of terms for each field:
F1/T1,T2,T3 F2/T4 F3/T5
When fields have multiple terms, this saves space. In unit
tests there is no additional waste even in the case that a field
has only a single value.
Here are the results of an indexing test case (beer-search):
$ benchcmp indexing-before.txt indexing-after.txt
benchmark old ns/op new ns/op delta
BenchmarkIndexing-4 11275835988 10745514321 -4.70%
benchmark old allocs new allocs delta
BenchmarkIndexing-4 25230685 22480494 -10.90%
benchmark old bytes new bytes delta
BenchmarkIndexing-4 4802816224 4741641856 -1.27%
And here are the results of a MatchAll search building a facet
on the "abv" field:
$ benchcmp facet-before.txt facet-after.txt
benchmark old ns/op new ns/op delta
BenchmarkFacets-4 439762100 228064575 -48.14%
benchmark old allocs new allocs delta
BenchmarkFacets-4 9460208 3723286 -60.64%
benchmark old bytes new bytes delta
BenchmarkFacets-4 260784261 151746483 -41.81%
Although we expect the index to be smaller in many cases, the
beer-search index is about the same in this case. However,
this may be due to the underlying storage (boltdb) in this case.
Finally, the index version was bumped from 5 to 7, since smolder
also used version 6, which could lead to some confusion.
