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ASF GitHub Bot commented on DRILL-6089: --------------------------------------- Github user HanumathRao commented on the issue: https://github.com/apache/drill/pull/1117 @ilooner Changes look fine to me. However, as discussed offline I couldn't reproduce the plan which was sorting one of the inputs for a HASHJOIN. This might be because in the hashjoinprule we are not asking for those traits in the first place. However, I do agree that this fix can be a safegaurd in case if that plan happens to show up in some scenarios. Thanks for the fix. > Validate That Planner Does Not Assume HashJoin Preserves Ordering for FS, > MaprDB, or Hive > ----------------------------------------------------------------------------------------- > > Key: DRILL-6089 > URL: https://issues.apache.org/jira/browse/DRILL-6089 > Project: Apache Drill > Issue Type: Improvement > Affects Versions: 1.13.0 > Reporter: Timothy Farkas > Assignee: Timothy Farkas > Priority: Major > Fix For: 1.13.0 > > > Explanation provided by Boaz: > (As explained in the design document) The new "automatic spill" feature of > the Hash-Join operator may cause (if spilling occurs) the rows from the > left/probe side to be returned in a different order than their incoming order > (due to splitting the rows into partitions). > Currently the Drill planner assumes that left-order is preserved by the > Hash-Join operator; therefore if not changes, a query relying on that order > may return wrong results (when the Hash-Join spills). > A fix is needed. Here are few options (ordered from the simpler down to the > most complex): > # Change the order rule in the planner. Thus whenever an order is needed > above (downstream) the Hash-Join, the planner would add a sort operator. That > would be a big execution time waste. > # When the planner needs the left-order above the Hash-Join, it may assess > the size of the right/build side (need statistics). If the right side is > small enough, the planner would set an option for the runtime to avoid > spilling, hence preserving the left-side order. In case spilling becomes > necessary, the code would return an error (possibly with a message suggesting > setting some special option and retrying; the special option would add a sort > operator and allow the hash-join to spill). > # When generating the code for the fragment above the Hash-Join (where > left-order should be maintained) - at code-gen time check if the hash-join > below spilled, and if so, add a sort operator. (Nothing like that exists in > Drill now, so it may be complicated). -- This message was sent by Atlassian JIRA (v7.6.3#76005)