Performance Tuning Guide - EMC Community Network

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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
Chapter 8 Maintaining the Repository and BAM Databases This chapter provides guidelines for maintaining the system databases and includes the following topics: • Maintaining the repository database, page 85 • Maintaining the BAM database, page 86 xCP applications frequently query databases for process data. Over time, the database tables can grow significantly, which affects query and application performance. Periodic maintenance of the repository and BAM databases can help keep application performance at the same levels as when the application was new. Maintaining the repository database Periodic database maintenance can prevent significant and sudden reductions in system performance (throughput or response time). The following workflow processing and task lookup tables cause roughly 80% of database performance problems. • Dm_workflow_s • Dm_sysobject_s • Dm_process_s • Dmi_workitem_s • Dmi_queue_item_s These tables usually have many inserts and deletes and can become quickly fragmented. If you notice performance issues, examine the statistics for the table indexes. Pay close attention to the dmi_queue_item_s, which can quickly grow into millions of rows. Existence of any entries that have the user name dm_fulltext_index_user indicates a problem. Note: If your system does not use the embedded xCP full-text search server, disable the system from writing entries to the dmi_queue_item_s table. EMC Documentum xCP 1.0 Performance Tuning Guide 85
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