Before the query extraction would have been aborted and the percolator query would be marked as unknown.
This resulted in a situation that these queries always need to be evaluated by the memory index at search time.
By adding support for this query many more percolator query candidate hits can skip the expensive memory index verification step. For example the `match` query parser returns a MatchNoDocsQuery if the query terms are removed by text analysis (lets query text only contained stop words).
Before 5.0 for it was required that the percolator queries were cached in jvm heap as Lucene queries for two reasons:
1) Performance. The percolator evaluated all percolator queries all the time. There was no pre-selecting queries that are likely to match like we have today.
2) Updates made to percolator queries were visible in realtime, Today these changes are visible in near realtime. So updating no longer requires the percolator to have the queries in jvm heap.
So having the percolator queries in jvm heap via the percolator cache is now less attractive. Especially when there are many percolator queries then these queries can consume many GBs of jvm heap.
Removing the percolator cache does make the percolate query slower compared to how the execution time in 5.0.0-alpha1 and alpha2, but it is still faster compared to 2.x and before.
Isabel Drost-Fromm
Martijn van Groningen
Isabel Drost-Fromm