I just hit this on
LUCENE-1516, which returns a cloned readOnly
readers from IndexWriter.
The problem is, when cloning, we create a new [thin] cloned
SegmentReader for each segment. FieldCache keys directly off this
object, so if you clone the reader and do a search that requires the
FieldCache (eg, sorting) then that first search is always very slow
because every single segment is reloading the FieldCache.
This is of course a complete showstopper for
With LUCENE-831 we'll switch to a new FieldCache API; we should ensure
this bug is not present there. We should also fix the bug in the
current FieldCache API since for 2.9, users may hit this.