https://bz.apache.org/bugzilla/show_bug.cgi?id=58489
Bug ID: 58489
Summary: QueryStatsComparator throws IllegalArgumentException:
Comparison method violates its general contract!
Product: Tomcat Modules
Version: unspecified
Hardware: All
OS: All
Status: NEW
Severity: major
Priority: P2
Component: jdbc-pool
Assignee: dev@tomcat.apache.org
Reporter: have...@gmail.com
Created attachment 33177
--> https://bz.apache.org/bugzilla/attachment.cgi?id=33177&action=edit
JUnit test to show the exception
Overview:
QueryStatsComparator may throw java.lang.IllegalArgumentException: Comparison
method violates its general contract!
This happens in specific situations depending on the data in the reported
queries. In our environment this occurs every time we keep the server running
until the maxCapacity (1000 items) is reached and the removeOldest method is
called. I have managed to narrow down the test data from more than 1000 records
to around 40 items and created a JUnit test to showcase the error. I needed to
copy some parts out of the SlowQueryReport class and made some simplifications
as the QueryStatsComparator is not reachable from outside.
Steps to Reproduce:
Please use the attached JUnit source code to reproduce this error.
Additional Builds and Platforms:
This bug seems to happen on all platforms.
We are using Tomcat 8, tomcat-dbcp 8.0.24, JDK 1.80.0_60.
Additional Information:
It seems to be a problem of the first two lines of the QueryStatsComparator.
Note that a single change in the data of the unit test may cause the Exception
not to occur.
Stacktrace:
java.lang.IllegalArgumentException: Comparison method violates its general
contract!
at java.util.TimSort.mergeLo(TimSort.java:773)
at java.util.TimSort.mergeAt(TimSort.java:510)
at java.util.TimSort.mergeCollapse(TimSort.java:435)
at java.util.TimSort.sort(TimSort.java:241)
at java.util.Arrays.sort(Arrays.java:1512)
at java.util.ArrayList.sort(ArrayList.java:1454)
at java.util.Collections.sort(Collections.java:175)
at
org.apache.tomcat.jdbc.pool.interceptor.SlowQueryReport.removeOldest(SlowQueryReport.java:218)
at
org.apache.tomcat.jdbc.pool.interceptor.SlowQueryReport.getQueryStats(SlowQueryReport.java:205)
at
org.apache.tomcat.jdbc.pool.interceptor.SlowQueryReport.reportQuery(SlowQueryReport.java:119)
at
org.apache.tomcat.jdbc.pool.interceptor.AbstractQueryReport$StatementProxy.invoke(AbstractQueryReport.java:254)
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