[IMPALA-5602] All predicates pushed to Kudu with limit runs incorrectly as 'small query'

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: Impala 2.8.0
• Fix Version/s: Impala 2.10.0
• Component/s: Frontend
• Labels: kudu
• Target Version: Impala 2.10.0
• Epic Color: ghx-label-2
• Assignee: Bikramjeet Vig
• Reporter: Matthew Jacobs
• Created: 29/Jun/17 23:04
• Updated: 15/Feb/24 02:07
• Resolved: 25/Aug/17 00:13

Description

When Kudu scans have predicates pushed to Kudu, the base implementation of ScanNode.getInputCardinality() is wrong:

  @Override
  public long getInputCardinality() {
    if (getConjuncts().isEmpty() && hasLimit()) return getLimit();
    return inputCardinality_;
  }

getConjuncts() won't contain the predicates pushed to Kudu. If such a query has a limit and there aren't any conjuncts applied at the scan node, then this function will return the limit as the input cardinality mistakenly.

This can result in a query running with the "small query" optimization when it should not be, i.e. it runs on a single node with a single scanner thread.