Performance Tuning Guide - EMC Community Network

Measuring Performance
Assessing database bottlenecks and dead waits
Bottleneck (Assessing capacity bottlenecks, page 84) and dead waits (Assessing dead waits, page 84)
indicate system sizing issues.
Assessing capacity bottlenecks
Capacity bottlenecks involve points in the system waiting for disk I/O to complete. For Oracle
databases, the DBWR (Database Writer) is a single point of serialization. Disk I/O directly relates to
the number of redo logs generated.
Logical I/O (LIO) can easily become Physical I/O (PIO) in a large volume system. At a certain point,
you can no longer cache.
A full index scan of 10 million table rows, with index that has 256 bytes per row, still reads 2.3 GB of
index data, which puts demands on resources (CPU, memory, disk I/O).
• Look for heavy LIO/PIO service activity in the database statspack.
• Look at AUTOTRACE execution paths and statement statistics for suspect queries.
• Figure out how often LIO/PIO statistics get run with number of users on the system and
extrapolate the I/O load on the system.
Assessing dead waits
Dead waits occur when multiple processes (or users) try to update a locked database row, resulting in
a race condition. Asynchronous event handling can also cause race conditions, even if your process
design effectively partitions the workload.
Carefully design your process to partition the workload and ensure workload partitioned updates do
not conflict with agent-based updates.
84 EMC Documentum xCP 1.0 Performance Tuning Guide