[DERBY-4977] XPLAIN reports negative EXECUTE_TIME for some parts of a join

• Type: Bug
• Status: Open
• Priority: Minor
• Resolution: Unresolved
• Affects Version/s: 10.7.1.1
• Component/s: SQL
• Labels: derby_triage10_8
• Urgency: Low
• Issue & fix info: Repro attached
• Assignee: Unassigned
• Reporter: Knut Anders Hatlen
• Created: 18/Jan/11 10:35
• Updated: 16/Feb/11 01:10

Description

I see that if I execute a join against the system tables with XPLAIN and statistics timing enabled, some of the rows in SYSXPLAIN_RESULTSET_TIMINGS have negative values in the EXECUTE_TIME column.

Here are the contents of the SYSXPLAIN_RESULTSET_TIMINGS after two runs with the attached repro script:

ij> select execute_time from my_schema.sysxplain_resultset_timings;
EXECUTE_TIME
--------------------
-1
0
0
-6
9
16

6 rows selected

ij> select execute_time from my_schema.sysxplain_resultset_timings;
EXECUTE_TIME
--------------------
-1
1
0
-7
10
15

6 rows selected

Note the two rows with negative values in both of the examples.