Branch Behavior of a Commercial OLTP Workload on Intel IA32 Processors

This paper presents a detailed branch characterization of an Oracle based commercial on-line transaction processing workload, Oracle Database Benchmark (ODB), running on an IA32 processor. We ran a welltuned ODB on Simics, a full system simulator, to collect the instruction traces used in this study. We compare the branch behavior of ODB with the branch behaviors of gcc, gzip and mcf from the SPECINT 2000 benchmark suite. Contrary to the popular belief that databases have unpredictable branches, we show that using larger predictors that capture enough branch history information, and using branch prediction schemes that reduce aliasing, conditional branches in ODB are more predictable than in gcc, gzip and mcf. Due to frequent context switching in ODB, a hardware return address stack is ineffective in predicting return addresses for ODB. Based on further analysis, we propose and evaluate an enhanced return address predictor, which reduces return address mispredictions in ODB by 40%.