[DOCS-13650] Investigate changes in SERVER-47972: maxTimeMS set on hedged requests does not give shards enough time to refresh Created: 15/May/20  Updated: 13/Nov/23  Due: 22/May/20  Resolved: 18/May/20

Status: Closed
Project: Documentation
Component/s: manual
Affects Version/s: None
Fix Version/s: 4.4.0-rc7, 4.7.0, Server_Docs_20231030, Server_Docs_20231106, Server_Docs_20231105, Server_Docs_20231113

Type: Task Priority: Major - P3
Reporter: Backlog - Core Eng Program Management Team Assignee: Kay Kim (Inactive)
Resolution: Fixed Votes: 0
Labels: docs-sharding
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

Issue Links:
Documented
documents SERVER-47972 maxTimeMS set on hedged requests does... Closed
Participants:
Days since reply: 3 years, 38 weeks, 2 days ago
Epic Link: DOCS: 4.4 Server Release Work

 Description   

Description

Downstream Change Summary

We've increased the default for maxTimeMSForHedgedReads here.

Description of Linked Ticket

Goal: investigate if the scenario outlined below is possible and determine a fix. 

 

Scenario:

Suppose shard0 has a primary, secondary0, and secondary1.

  • Each time mongos tries to perform 'count' with hedged reads, secondary0 never gets the chance to set the in memory database version because it either gets killedOp'd or timed out of maxTimeMS before it can be set successfully after refreshing.
  • Over the NetworkInterfaceTL, mongos tries to route the next 'count' command to secondary0. Secondary0 has no known databaseVersion, so onDbVersionMismatchNoExcept gets called. A refresh is prompted and errors with maxTimeMS expiration error.
  • Since the maxTimeMS error is ignored, the original "no known dbVersion" error propagates back to the NetworkInterfaceTL. There, since the error reported is not maxTimeMS, the finish line is triggered. Secondary0 wins the race, but the 'count' fails with "don't know dbVersion."

In this scenario, we believe secondary0 would be getting killed here.

Scope of changes

Impact to Other Docs

MVP (Work and Date)

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



 Comments   
Comment by Githook User [ 18/May/20 ]

Author:

{'name': 'Kay Kim', 'email': 'kay.kim@10gen.com', 'username': 'kay-kim'}

Message: DOCS-13650: update default for maxTimeMSForHedgedReads
Branch: master
https://github.com/mongodb/docs/commit/4d7c5d737b571a8371581bfe79a0a6b5fc82b02b

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