public Map<String, ColumnStatsList> getColStatsCache() {
    return colStatsCache;
  }
A subset of compilation context that is passed to operators to get rid of some globals.
Perhaps this should be rolled into main Context; however, some code necessitates storing the
context in the operators for now, so this may not be advisable given how much stuff the main
Context class contains.
For now, only the operator sequence ID lives here.
ql/src/java/org/apache/hadoop/hive/ql/CompilationOpContext.java