  In this paper, we focus on studying duplicate logging statements, which are
logging statements that have the same static text message. We manually studied
over 4K duplicate logging statements and their surrounding code in five
large-scale open source systems. We uncovered five patterns of duplicate
logging code smells. For each instance of the duplicate logging code smell, we
further manually identify the potentially problematic and justifiable cases.
Then, we contact developers to verify our manual study result. We integrated
our manual study result and the feedback of developers into our automated
static analysis tool, DLFinder, which automatically detects problematic
duplicate logging code smells. We evaluated DLFinder on the five manually
studied systems and three additional systems. In total, combining the results
of DLFinder and our manual analysis, we reported 91 problematic duplicate
logging code smell instances to developers and all of them have been fixed. We
further study the relationship between duplicate logging statements, including
the problematic instances of duplicate logging code smells, and code clones. We
find that 83% of the duplicate logging code smell instances reside in cloned
code, but 17% of them reside in micro-clones that are difficult to detect using
automated clone detection tools. We also find that more than half of the
duplicate logging statements reside in cloned code snippets, and a large
portion of them reside in very short code blocks which may not be effectively
detected by existing code clone detection tools. Our study shows that, in
addition to general source code that implements the business logic, code clones
may also result in bad logging practices that could increase maintenance
difficulties.
