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Original Description

Description:

The "queryHash" is now present in planCacheListPlans and planCacheListQueryShapes output. We may wish to document this in pages about these debug mechanisms? Right now it looks like we don't have detailed documentation about the output of these commands – I think we might want to keep it that way, in order to prevent users from depending too much on the particular format. These commands are mostly for use by TSEs or others who are diagnosing query performance issues.

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-23332 added this same 'queryHash' to the logs and system.profile, and https://jira.mongodb.org/browse/SERVER-36527 added it to explain output.

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Description

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

• reference/glossary  (when working on linked tickets, will touch core/query-plans)
• 4.2
• db.collection.getPlanCache().listQueryShapes()
• db.collection.getPlanCache().getPlansByQuery(query[, projection, sort, collation]) - displays the cached plans for a query shape
• db.collection.getPlanCache().clearPlansByQuery() 
• planCacheListPlans
• planCacheClear
• planCacheListQueryShapes

note: we're missing collation from the plancache methods/commands – but will do it as a separate ticket in order to backport just those through 3.4.

Impact to other docs outside of this product

MVP (work and date?)

Resources (e.g. Scope Docs, Invision)