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Chapter 8. Statistics (aggregates)

Aggregate instances are used to collect statistics on numerical values, when it is important to accumulate new data quickly and in large volume. These instances operate without exclusive locks, and store only aggregated stream statistics. Aggregates make sense only for global variables. They are stored individually or as elements of an array.

8.1. The aggregation (<<<) operator

The aggregation operator is “<<<”, and its effect is similar to an assignment or a C++ output streaming operation. The left operand specifies a scalar or array-index l-value, which must be declared global. The right operand is a numeric expression. The meaning is intuitive: add the given number to the set of numbers to compute their statistics. The specific list of statistics to gather is given separately by the extraction functions. The following is an example. 
a <<< delta_timestamp
writes[execname()] <<< count