Affects Version/s: 5.0, 5.1, 5.2, 5.3, 6.0
Fix Version/s: None
Use of the highly optimized faceting that Solr had for multi-valued fields over relatively static indexes was removed as part of
LUCENE-5666, causing severe performance regressions.
Here are some quick benchmarks to gauge the damage, on a 5M document index, with each field having between 0 and 5 values per document. Higher numbers represent worse 5x performance.
Solr 5.4_dev faceting time as a percent of Solr 4.10.3 faceting time
|...................................||Percent of index being faceted|
For example, a field with 1000 unique values in the whole index, faceting with 5x took 143% of the 4x time, when ~10% of the docs in the index were faceted.
One user who brought the performance problem to our attention: http://markmail.org/message/ekmqh4ocbkwxv3we
"faceting is unusable slow since upgrade to 5.3.0" (from 4.10.3)
The disabling of the UnInvertedField algorithm was previously discovered in
SOLR-7190, but we didn't know just how bad the problem was at that time.
edit: removed "secret" adverb by request