SlowAtomicReader is of course slow, and it's getLiveDocs (based on MultiBits) is slow as it uses a binary search for each lookup. There are various places in Solr that use SolrIndexSearcher.getSlowAtomicReader and then get the liveDocs. Most of these places ought to work with SolrIndexSearcher's getLiveDocs method.
- is related to
SOLR-13851 SolrIndexSearcher.getFirstMatch trips assertion if multiple matches