jpountz opened a new pull request, #12810:
URL: https://github.com/apache/lucene/pull/12810
Currently `advance(int target)` needs to perform two checks:
- is there a need to use skip lists?
- is there a need for decoding a new block?
Ideally we would track the last doc ID in a block and use it to check these
two things with a single comparison. However neither `accum` nor `nextSkipDoc`
are suitable for this because they both start at 0, so `advance(0)` on an
postings enum that is not initialized would think that it doesn't need to
decode a new block while it does.
Instead of introducing a 3rd variable, this PR changes postings and skip
lists to start at -1 so that checking `target > accum` is enough to know
whether skip lists may need to be advanced and a new block needs to be decoded.
Specifically, check out changes to `BlockImpactsEnum#advance` which is now
simpler.
This feels like a good change anyway, as now a value that would be present
in every single document would be able to take advantage of the `allEqual`
optimization on the first block, which currently fails because the first doc
delta is 0, while all other deltas are 1.
This also enabled a few other simplifications, see e.g. `BlockDocsEnum` and
`EverythingEnum`, which no longer need to track the `nextSkipDoc` and can do
everything they need using `accum`.
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