Sampling for DB2 is the same as sampling for any other target. At specified intervals, data is collected about the target. The more samples collected from the same location within the target, the better areas that might have tuning opportunities are identified. For DB2, the area within the target is identified by a DB2 SQL statement. The more samples that are taken during the execution of a SQL statement, the higher the probability that a tuning opportunity exists.
The principle drawback for sampling DB2 is that DB2 reuses structures. When a sample is taken there is a chance that the data in the object being sampled is left over from a previous call to DB2. CA MAT uses a number of techniques to resolve any discrepancies, but they may occur, especially when collecting the source of the SQL statement. The SQL statement is collected from other sources as well as sampling.
Sampling is not the only source of the SQL statement.
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