Detecting Diamond Necklaces in Labeled Dags (A Problem from Distributed Debugging)

Overview & Synopsis

The problem tackled in this paper originates from the debugging of distributed applications. Execution of such an application can be modeled as a partially ordered set of process states. The debugging of control flows (sequences of process states) of these executions is based on the satisfaction of predicates by process states. A process state that satisfies a predicate inherits its label. It follows that, in this context, a distributed execution is a labeled directed acyclic graph (dag for short). Debug or determine if control flows of a distributed execution satisfies some property amounts to test if the labeled dag includes some pattern defined on predicate labels. This paper first introduces a general pattern (called diamond necklace) which includes classical patterns encountered in distributed debugging. Then an efficient polynomial time algorithm detecting such patterns in a labeled dag is presented. To be easily adapted to an on-the-fly detection of the pattern in distributed executions, the algorithm visits the nodes of the graph according to a topological sort strategy.