We are currently on an older release v1.6.6 and should move on to the latest v1.7.5 to pick up performance improvements etc.
From the changelog:
"performance improvements: The logger factories in most SLF4J modules namely in jcl-over-slf4j, log4j-over-slf4j, slf4j-jcl, slf4j-jdk14, slf4j-log4j12, and slf4j-simple now use a ConcurrentHashMap instead of a regular HashMap to cache logger instances. This change significantly improves logger retrieval times at the cost of some memory overhead. This improvement was requested in bug #298 by Taras Tielkes who also provided the relevant patch.
Given the significance of these performance improvements, users are highly encouraged to migrate to SLF4J version 1.7.5 or later. "