[DOCS-12651] Clarify triggering events for the query replanning mechanism Created: 24/Apr/19  Updated: 30/Oct/23  Resolved: 30/Jun/23

Status: Closed
Project: Documentation
Component/s: manual
Affects Version/s: None
Fix Version/s: Server_Docs_20231030

Type: Task Priority: Critical - P2
Reporter: Chris Harris Assignee: Joseph Dougherty
Resolution: Won't Fix Votes: 0
Labels: ready-for-work, reopened, server-docs-bug-bash
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

Issue Links:
Related
related to DOCS-16236 Add "replanner" section to Query Plans Backlog
Participants:
Days since reply: 35 weeks, 5 days ago
Epic Link: DOCSP-26173

 Description   

Description

The plan cache replanning mechanism can get triggered as outlined in this comment from SERVER-21064:

This is fixed by SERVER-15225, which eliminated the notion of a cached "backup plan" and replaced it with the notion of "replanning". When this scenario occurs on a version where replanning is enabled by default (3.0.7 and higher), the cached plan hitting the 32 MB limit will cause us to restart plan selection from the beginning. We generate and rank several candidate plans, and correctly select the non-blocking plan as the winner.

Presently the Query Plans page contains the following:

If a matching entry exists, the query planner generates a plan based on that entry and evaluates its performance through a replanning mechanism. This mechanism makes a pass/fail decision based on the plan performance

Usage of the word "performance" here may be too ambiguous. It is unclear if a failed execution (resulting from exceeding the sort threshold using the cached plan) would be considered simply an evaluation of its performance. More details about the events that trigger the replanning mechanism could help reduce confusion about replanned:1 entries in the log file.

Scope of changes

Impact to Other Docs

MVP (Work and Date)

Resources (Scope or Design Docs, Invision, etc.)



 Comments   
Comment by Emet Ozar [ 02/Jun/23 ]

This ticket is blocked on external review feedback

Comment by David Hou [ 28/Nov/22 ]

christopher.harris@mongodb.comian.boros@mongodb.comdavid.storch@mongodb.comcharlie.swanson@mongodb.com,

Hi all, the updated query plan flow chart was recently completed in DOCS-13987. Was there any resolution to the discussion for this ticket and are documentation changes still needed? Thanks!

Comment by Emet Ozar [ 27/Oct/22 ]

christopher.harris@mongodb.com Hey Christopher, is this still a documentation problem? Thank you, Emet CC: sarah.olson@mongodb.com ashley.brown@mongodb.com 

Comment by Ian Boros [ 06/May/19 ]

Filed DOCS-12664 for the updated flow chart.

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