[PHOENIX-3152] Incorrect comparator in QueryOptimizer may cause IllegalArgumentException

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 4.8.0
• Assignee: Sergey Soldatov
• Reporter: Sergey Soldatov
• Created: 05/Aug/16 22:47
• Updated: 07/Aug/16 04:41
• Resolved: 07/Aug/16 02:47

Description

The problem code is in QueryOptimizer#orderPlansBestToWorst
When we have a lot of local similar indexes, all of them comes to the array of best candidates. After that we try to sort them using our own Comparator. In the compare we check first:
1. bound pk columns count
2. groupBy order
3. number of columns
for two local indexes on different columns first 3 steps always passed (since they are equal)
And now we execute the following checks:

                // If all things are equal, don't choose local index as it forces scan
                // on every region (unless there's no start/stop key)
                if (table1.getIndexType() == IndexType.LOCAL) {
                    return plan1.getContext().getScanRanges().getRanges().isEmpty() ? -1 : 1;
                }
                if (table2.getIndexType() == IndexType.LOCAL) {
                    return plan2.getContext().getScanRanges().getRanges().isEmpty() ? 1 : -1;
                }

obvious that for similar two plans with similar scan ranges compare (plan1, plan2) and compare(plan2, plan1) will return the same result (1 if ranges are not empty, -1 otherwise). This may cause following exception from Collections.sort :

	at java.util.TimSort.mergeLo(TimSort.java:777)
	at java.util.TimSort.mergeAt(TimSort.java:514)Listening for transport 	at java.util.TimSort.mergeCollapse(TimSort.java:441)
	at java.util.TimSort.sort(TimSort.java:245)
	at java.util.Arrays.sort(Arrays.java:1512)
	at java.util.ArrayList.sort(ArrayList.java:1454)
	at java.util.Collections.sort(Collections.java:175)

I would suggest to add a check that if both plans are local indexes, then consider them equal, otherwise execute the check. James R. Taylor, ramkrishna.s.vasudevan any thoughts?

Ankit Singhal FYI