Summary

Provide a low-cost histogram in mongod that measures the execution time of reads, writes, and database commands.

Motivation

Currently, there is only a limited number of ways to inspect the performance of a running MongoDB instance. While the system profiler does provide detailed information about “slow” operations, profiling all operations is prohibitively expensive. This project aims to implement a lightweight histogram component in the database with negligible runtime impact, which would allow it to be on by default and allow all operations to be recorded in a useful fashion. The global histogram output will also be included in serverStatus statistics.

Documentation

Scope Document
Design Document

Docs Changes

• $collStats aggregation stage
• db.collection.latencyStats() shell helper
• serverStatus.metrics change