[SERVER-34998] Ignore oplog timeout in serverStatus opLatencies Created: 15/May/18  Updated: 13/Jun/18  Resolved: 05/Jun/18

Status: Closed
Project: Core Server
Component/s: Diagnostics, Querying
Affects Version/s: 3.4.15
Fix Version/s: None

Type: Improvement Priority: Minor - P4
Reporter: Kevin Arhelger Assignee: David Storch
Resolution: Duplicate Votes: 3
Labels: None
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

Issue Links:
Duplicate
duplicates SERVER-29304 Exclude time spent blocking for await... Closed
Related
related to SERVER-25180 Make latency histogram collection opt... Closed
Sprint: Query 2018-06-18
Participants:
Case:

 Description   

The opLatencies section of serverStatus was added in MongoDB 3.4. These metrics are collected by FTDC, Ops Manager/Cloud Manager monitoring, and third party tools.

On an idle replica set, read latencies can be observed in the 5000ms range due to replication timeout.

This is confusing for anyone observing these metrics and they may believe there is a performance problem, solely based on these artifacts. When a steady write load is applied, these metrics even out.

Splitting oplog latencies out from this metric would prevent this confusion, but still allow diagnosis of replication issues.



 Comments   
Comment by David Storch [ 05/Jun/18 ]

kevin.arhelger, excluding time spent blocking for awaitData from various debug output, including db.serverStatus().opLatencies was implemented in SERVER-29304 for version 3.5.9. I see that this ticket is marked with an "Affects Version" of both 3.6.4 and 3.7.9. Have you tested to confirm that 3.6.x and 3.7.x exhibit the behavior described by this ticket?

I'm closing this ticket as a duplicate of SERVER-29304. If there is some defect in the behavior implemented in SERVER-29304, or you would like to request additional functionality beyond what was implemented in SERVER-29304, feel free to re-open.

Comment by Bruce Lucas (Inactive) [ 15/May/18 ]

I don't recall seeing these logged as slow operations in mongod log. I wonder why they show up in opLatencies and not the log? In any case agreed these aren't really op latencies.

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