HammerDB: Avoiding bottlenecks in client.

Posted on by gary

How to avoid bottlenecks in the client generator when measuring database performance with HammerDB

HammerDB is a great tool for running Database benchmarks. However it is very easy to create an artificial bottleneck which will give a very poor benchmark result.

When setting up HammerDB to run against even a moderate modern server, it is important to avoid displaying the client transaction outputs in the HammerDB UI.

In my case just making this simple changed increased my HammerDB results by over 6X. The reason is that HammerDB spends more time updating its own UI, than it does sending transactions to the DB. When I run HammerDB, I select “Log Output to Temp” and “Use Unique Log Name”.

  • Either:
    • Un-check the “Show results” mark.
    • Or Ensure that the results are logged to file, not displayed on screen
  • Otherwise the workload generator will become the bottleneck.
Checked -> 124,000 tpm
Un-Checked -> 800,000 tpm<
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Show Output "Checked"





Show Output "Un-Checked"





HammerDB with "Show results" unchecked. SQL Server uses all the CPU (99%)





HammerDB with "Show results" checked. SQL Servr using ~20% HammerDB driver (Identified as wish86t) is using 99% of one CPU.