1. When
Do Changes Induce Fixes?
On Fridays.
Jacek Śliwerski, Thomas Zimmermann, Andreas Zeller
Saarland University

2. The Risk of Change
Which changes go wrong?
How do we find such “bad” changes?
What can we do with them?
Idea:
combine bug databases + version archives
=> locate fix-inducing changes

3. The Risk of Change
Which changes go wrong?
How do we find such “bad” changes?
What can we do with them?
Idea:
combine bug databases + version archives
=> locate fix-inducing changes

4. Fix-Inducing Changes
Fix-Inducing Changes are
Changes that lead to problems as
indicated by later fixes.
Later:
Example:
... ...
if (foo==null) { if (foo!=null) {
foo.bar(); foo.bar();
FIX-INDUCING FIX

5. How to
Locate Fix-Inducing Changes

6. How to
Locate Fix-Inducing Changes
$ cvs annotate -r 1.17 Foo.java
...
19: 1.11 (john 12-Feb-03): public int a() {
20: 1.11 (john 12-Feb-03): return i/0;
...
39: 1.10 (mary 12-Jan-03): public int b() {
40: 1.14 (kate 23-May-03): return 42;
...
59: 1.10 (mary 17-Jan-03): public void c() {
60: 1.16 (mary 10-Jun-03): int i=0;
1.18
Fixed Bug
42233
Changed:
a() b() c()
line 20 40 60

7. How to
Locate Fix-Inducing Changes
$ cvs annotate -r 1.17 Foo.java
20: 1.11 (john 12-Feb-03): return i/0;
40: 1.14 (kate 23-May-03): return 42;
60: 1.16 (mary 10-Jun-03): int i=0;
1.11 1.14 1.16 1.18
a() was b() was c() was Fixed Bug
changed changed changed 42233
Changed:
FIX-INDUCING FIX-INDUCING FIX-INDUCING
a() b() c()

8. Bug
How to
Locate Fix-Inducing Changes
$ cvs annotate -r 1.17 Foo.java
20: 1.11 (john 12-Feb-03): return i/0;
40: 1.14 (kate 23-May-03): return 42;
60: 1.16 (mary 10-Jun-03): int i=0;
Bug 42233 was reported. closed.
1.11 1.14 1.16 1.18
a() was b() was c() was Fixed Bug
changed changed changed 42233
Changed:
FIX-INDUCING FIX-INDUCING FIX-INDUCING
a() b() c()
BUG-INDUCING

9. Bug-Inducing Changes
are Indicators for Risk

10. Large Transactions
are Risky
Average Number of Changed Files
Bug- Not Bug-
All
Inducing Inducing
Fix
Not a Fix
All 3.52
ECLIPSE, for MOZILLA the average is 3.58.

11. Large Transactions
are Risky
Average Number of Changed Files
Bug- Not Bug-
All
Inducing Inducing
Fix 2.73
Not a Fix 3.81
All 3.52
ECLIPSE, for MOZILLA the other way round.

12. Large Transactions
are Risky
Average Number of Changed Files
Bug- Not Bug-
All
Inducing Inducing
Fix 2.73
Not a Fix 3.81
All 7.49 2.61 3.52
ECLIPSE, for MOZILLA the same tendency.

13. Large Transactions
are Risky
Average Number of Changed Files
Bug- Not Bug-
All
Inducing Inducing
Fix 3.82 2.08 2.73
Not a Fix 11.30 2.77 3.81
All 7.49 2.61 3.52
ECLIPSE, for MOZILLA a different distribution.

14. Fridays are Risky,
Tuesdays are not ;-)
Frequency
11.3%
Monday 18.4%
20.9% of all changes
10.4%
Tuesday
on Tuesday are fixes,
20.9%
11.1%
10.4% induce bugs.
Wednesday 20.0%
12.1%
Thursday 22.3%
12.2%
Friday 24.0%
11.7%
Saturday 14.7%
11.6%
Sunday 16.9%
0% 5% 10% 15% 20% 25% 30% 35% 40%
Fixes
ECLIPSE
Bug-Inducing Changes

15. Fixes are very Risky
Likelihood
8.2%
Monday 25.1%
that a Change
7.1%
Tuesday 22.9%
is Bug-Inducing
8.1%
Wednesday 23.3%
22.9% of all fixes on
8.8%
Thursday
Tuesday induce bugs,
23.5%
only 7.1% of changes
8.7%
Friday 23.2%
for new features do.
8.4%
Saturday 30.3%
8.6%
Sunday 26.4%
0% 5% 10% 15% 20% 25% 30% 35% 40%
ECLIPSE Fixes New Features, Refactoring

16. Is MOZILLA broken?
Fix transactions are larger than regular
transactions (4.39 vs 3.05 files).
48.5% of all revisions are fixes,
41.5% induce later bugs.
A fix induces in 45.2% a later bugs,
regular changes in “only” 38.1%.

17. For earthquakes and crime rates...
Risk depends on Locations
The same with risk of changes!

18. resolveClasspath()
/* (non-Javadoc)
* @see org.eclipse.jdt.launching.IRuntimeClasspathProvider#resolveClasspath
* (org.eclipse.jdt.launching.IRuntimeClasspathEntry[], org.eclipse.debug.core.ILaunchConfiguration)
*/
public IRuntimeClasspathEntry[] resolveClasspath(IRuntimeClasspathEntry[] entries, ILaunchConfiguration configuration)
throws CoreException {
List all = new ArrayList(entries.length);
for (int i = 0; i < entries.length; i++) {
switch (entries[i].getType()) {
case IRuntimeClasspathEntry.PROJECT:
// a project resolves to itself for source lookup (rather than the class file output locations)
all.add(entries[i]);
break;
9 changes,
case IRuntimeClasspathEntry.OTHER:
IRuntimeClasspathEntry2 entry = (IRuntimeClasspathEntry2)entries[i];
if (entry.getTypeId().equals(DefaultProjectClasspathEntry.TYPE_ID)) {
all of them fixes
// add the resolved children of the project
IRuntimeClasspathEntry[] children = entry.getRuntimeClasspathEntries(configuration);
8 bug-inducing changes
IRuntimeClasspathEntry[] res = JavaRuntime.resolveSourceLookupPath(children, configuration);
for (int j = 0; j < res.length; j++) {
all.add(res[j]);
one re-implementation
}
}
break;
default:
IRuntimeClasspathEntry[] resolved =JavaRuntime.resolveRuntimeClasspathEntry(entries[i], configuration);
for (int j = 0; j < resolved.length; j++) {
all.add(resolved[j]);
}
break;
}
}
return (IRuntimeClasspathEntry[])all.toArray(new IRuntimeClasspathEntry[all.size()]);
}

20. Movie with
John Wayne
(1962)
Swahili for
“Danger”
HATARI
Raising Risk Awareness

21. HATARI: Annotations
Unrisky Location
(green)
Risky Location
(dark red)

22. Conclusion
Fix- and Bug-inducing changes are an
measure for (past) risk.
We make this risk visible for developers.
HATARI will be released in August 2005
http://www.st.cs.uni-sb.de/softevo/
Until then: Don’t program on Fridays! ;-)

23. Sign Gallery