benwtrent opened a new issue, #15561:
URL: https://github.com/apache/lucene/issues/15561
### Description
I have been digging into the AcceptDocs API and I noticed the following from
the java docs:
```
/**
* Return an approximation of the number of accepted documents. This is
typically useful to decide
* whether to consume these accept docs using random access ({@link
#bits()}) or sequential access
* ({@link #iterator()}).
*
* <p><b>NOTE</b>: This must not be called after {@link #iterator()}.
*
* @return approximate cost
*/
public abstract int cost() throws IOException;
```
However the implementation for the most common non-cached iterator:
```
public int cost() throws IOException {
createBitSetAcceptDocsIfNecessary();
return acceptBitSet.cardinality();
}
```
Actually fully consumes the iterator and just calls cardinality (nothing
approximate at all...).
Why are we doing that? Why aren't we relying on `DocIdSetIterator#cost` or
at least `acceptBitSet.cardinality`?
It seems to me the main idea behind AcceptDocs is the ability to bypass
realizing the bitset and to just iterate as normal when the filter is very
restrictive...
//cc @shubhamvishu
### Version and environment details
_No response_
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