[DOCS-5809] Explain how delayed secondaries apply the oplogs Created: 09/Jul/15  Updated: 30/Oct/23  Resolved: 24/May/18

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

Type: Improvement Priority: Minor - P4
Reporter: Daniel Coupal Assignee: Kay Kim (Inactive)
Resolution: Done Votes: 0
Labels: None
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

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Days since reply: 5 years, 38 weeks ago

 Description   

Could not find a place in the doc that describes how the delayed secondaries are applying oplogs.
The typical question is regarding if:

  1. they are read with a delay, then applied
  2. read immediately from the primary, but applied with a delay

The answer is 1.

This page may be a good place to add the info:
http://docs.mongodb.org/manual/core/replica-set-delayed-member/



 Comments   
Comment by Stennie Steneker (Inactive) [ 24/May/18 ]

The current Delayed Replica Set Members page describe this behaviour:

Delayed members copy and apply operations from the source oplog on a delay. When choosing the amount of delay, consider that the amount of delay:

  • must be equal to or greater than your expected maintenance window durations.
  • must be smaller than the capacity of the oplog. For more information on oplog size, see Oplog Size.

The "copy and apply" step requires the delayed secondary to have an oplog point in common with the source oplog.

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