Dynamic SQL Causing Lock Escalation?

Lock escalation is the promotion of a lock from a row, page or LOB lock to a table space lock because the number of page locks that are concurrently held on a given resource exceeds a preset limit.

But lock escalation can cause problems. Yes, when fewer locks are taken, CPU cost and memory usage can be reduced. On the other hand, escalating the size of a lock causes more resources to be locked... and that impacts concurrency with the most likely result being applications experiencing lock timeouts or deadlocks.

When lock escalation occurs, DB2 writes messages to the system log. So when complaints inevitably arrive about failing transactions you can look for the appropriate lock escalation message indicating that it could be the culprit.

But such simple steps are typically not sufficient to track down the root cause and take corrective actions. You need to be able to determine what SQL statement in what program and under what circumstances is causing the escalation. Doing so involves tracing and using performance monitoring tools.

For those interested in this topic, (indeed, the primary purpose of this blog post) you should seek out the IBM TechDoc titled Identifying the dynamic SQL statement which is causing a
lock escalation in DB2 for z/OS. For those who don't know what a TechDoc is, don't worry, it isn't that complicated. It is basically a published piece of technical documentation that isn't part of a larger manual or IBM RedBook. They can be short papers, product flashes, presentations, etc.

This particular TechDoc details a methodology for identifying dynamic SQL statements involved in a lock escalation. It describes which traces to start, and which jobs to run to analyze the collected traces. It also explains how to analyze the trace report to find the problematic SQL statement.

You can search all of IBM's TechDocs by following this link.

Happy reading!