Package org.apache.drill.exec.store.base.filter

Interface FilterPushDownListener

All Known Implementing Classes:
GoogleSheetsPushDownListener, HttpPushDownListener, SplunkPushDownListener
public interface FilterPushDownListener
Call-back (listener) implementation for a push-down filter. Abstracts away the common work; plugins implement this class to do work specific to the plugin.

Supports two kinds of filter push down:

Conjunctive Normal Form (CNF)
A series of expressions joined by an AND: the scan should produce only rows that satisfy all the conditions.
Disjunctive Normal Form (DNF)
A series of alternative values for a single column, essentially a set of expressions joined by OR. The scan spits into multiple scans, each scanning one of the partitions (or regions or queries) identified by the case. This is an implementation of the SQL IN clause.

In both cases, the conditions are in the form of a ExprNode.ColRelOpConstNode in which one side refers to a column in the scan and the other is a constant expression. The "driver" will ensure the rel op is of the correct form; this class ensures that the column is valid for the scan and the type of the value matches the column type (or can be converted.)

The DNF form further ensures that all rel ops refer to the same column, and that only the equality operator appears in the terms.

  • Method Details

    • prefix

      String prefix()
      Returns:
      a prefix to display in filter rules

    • isTargetScan

      boolean isTargetScan(GroupScan groupScan)
      Broad check to see if the scan is of the correct type for this listener. Generally implemented as: 
       public boolean isTargetScan(ScanPrel scan) {
   return scan.getGroupScan() instanceof MyGroupScan;
 }
      Parameters:
      groupScan - the scan node
      Returns:
      true if the given group scan is one this listener can handle, false otherwise

    • builderFor

      FilterPushDownListener.ScanPushDownListener builderFor(GroupScan groupScan)
      Check if the filter rule should be applied to the target group scan, and if so, return the builder to use.

      Calcite will run this rule multiple times during planning, but the transform only needs to occur once. Allows the group scan to mark in its own way whether the rule has been applied.

      Parameters:
      groupScan - the scan node
      Returns:
      builder instance if the push-down should be applied, null otherwise