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Original Description

Description:

The "queryHash" is now present in slow query log lines and in system.profile output. We may wish to document this in pages about these debug mechanisms. All queries with the same hash are considered the same "shape", and use the same plan cache entry. This may be useful for diagnosing issues around query performance. Please ask Storch for more details, and to review any proposed documentation changes.

Note that https://jira.mongodb.org/browse/SERVER-35981 added this same 'queryHash' to the plan cache introspection commands output, and https://jira.mongodb.org/browse/SERVER-36527 added it to explain output.

Engineering Ticket Description:

It would be nice if we included a hash of all queries (without their binds) so we can get a sense for unique types of queries being run on a system and to be able to get a better performance profile for "bad" queries. If we could add that hash into the mongod.log we can easily "group" queries for prioritization when telling the customer what to "tweak".

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Description

Scope of changes (files that need work and how much)

• 4.2
• tutorial/manage-the-database-profiler
• /reference/database-profiler 
• source/tutorial/evaluate-operation-performance.txt
• administration/analyzing-mongodb-performance
• source/includes/fact-log-slow-queries.rst
• source/includes/options-mongod.yaml
• source/reference/log-messages.txt

Impact to other docs outside of this product

MVP (work and date?)

Resources (e.g. Scope Docs, Invision)