The P3 process is part of the VMX-Capture architecture. It is called P3 because it performs three functions: pre filtering, pre correlation, and pre aggregation.
Pre Filtering can be used to dynamically filter the output of one probe using input from another probe. Pre Correlation allows simple correlation across a network hop.
Pre Aggregation is similar to the pre aggregation that is performed in Stack Probes, and can be used in a situation where a single aggregation is required of a message volume that is too high for any individual probe to process on its own. The message load can be split between multiple stack probes, and these probe outputs can then be split between multiple P3 processes. P3 can then rollup buckets of distribution to VMX-Analysis, to get effective HDR distributions for high message volume calculations.