Github user katameru commented on a diff in the pull request: https://github.com/apache/phoenix/pull/281#discussion_r151620890 --- Diff: phoenix-core/src/main/java/org/apache/phoenix/optimize/QueryOptimizer.java --- @@ -91,8 +91,23 @@ public QueryPlan optimize(PhoenixStatement statement, SelectStatement select, Co } public QueryPlan optimize(QueryPlan dataPlan, PhoenixStatement statement, List<? extends PDatum> targetColumns, ParallelIteratorFactory parallelIteratorFactory) throws SQLException { - List<QueryPlan>plans = getApplicablePlans(dataPlan, statement, targetColumns, parallelIteratorFactory, true); - return plans.get(0); + List<QueryPlan> plans = getApplicablePlans(dataPlan, statement, targetColumns, parallelIteratorFactory, false); + if (plans.size() == 1) { + return plans.get(0); + } + + // Get the best plan based on their costs. Costs will be ZERO if stats are not + // available, thus the first plan will be returned. + Cost minCost = null; + QueryPlan bestPlan = null; + for (QueryPlan plan : plans) { + Cost cost = plan.getCost(); + if (minCost == null || cost.compareTo(minCost) < 0) { + minCost = cost; + bestPlan = plan; + } + } + return bestPlan; --- End diff -- I'd argue that the observable behavior should stay the same, so a hinted query plan should be used above all others. Currently we could just sidestep the cost calculations in favor of a hinted plan, but I think that having a way to influence the optimizer via hints could be very useful.
---