You can monitor queries using the Teradata Viewpoint Query Monitor portlet and other tools and utilities to identify poorly performing queries. Poor query performance is usually due to:
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Query Problem |
Result |
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Stale statistics |
The optimizer uses statistics to plan query execution. If the statistics are out of date, the optimizer may create a poor plan. Recommendation: Review tables to see whether statistics are out of date, and recollect statistics if required, as shown in Chapter 14: “Improving Query Performance Using COLLECT STATISTICS: Application DBAs.” |
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Badly skewed data |
Causes table rows to be distributed unevenly among AMPs and queries to execute unevenly, which slows processing time. Recommendation: Monitor table skew. Redefine the primary index if required. See “Finding and Fixing Skewed Tables” on page 247. |
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Poor query construction |
Poor SQL syntax or missed punctuation can result in bad queries. Recommendations: |
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Concurrency issues |
Some queries are delayed or prevented from executing because of lock contentions, or the relative priorities of concurrent queries. Recommendations: |