Oracle: Row source statistics

Oracle can be instructed to collect row source statistics. When enabled, Oracle will collect data for each row source (aka plan operations) of an execution plan.

Numbers collected include

• Total time spent executing a row source
• The number or rows the row source produced/returned
• Number of consistent and current gets
• Number of physical reads/writes

Collection of row source statistics is enabled by

• Setting event 10046
• Using the gather_plan_statistics hint
• Setting the init parameter statistics_level to all

The value of the init parameter _rowsource_statistics_sampfreq determines how often system time(?) is taken to measure amount of time spent in a row source operation. Lowering the value of _rowsource_statistics_sampfreq increases the accuracy per rowsource, but increases time spent to measure the values and thus the overall time («overhead») to execute an SQL statement.