[SERVER-51449] Mongodb unusually high iops during fsync mongoversion 3.2.10 Created: 09/Oct/20  Updated: 20/Oct/20  Resolved: 20/Oct/20

Status: Closed
Project: Core Server
Component/s: None
Affects Version/s: None
Fix Version/s: None

Type: Question Priority: Major - P3
Reporter: maneesh bhunwal Assignee: Edwin Zhou
Resolution: Done Votes: 0
Labels: None
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

Participants:

 Description   

we have mongodb with 1 primary and 2 secondaries. On primary node the disk write iops are spiking every minute and latencies go up.
Looking further write iops seems like a bottle neck. so we reduced the fsyc time to 10 sec from 60 sec (default).

It has helped us a lot but still the write iops on 60 qps update are around 1300 in every fsync.

I did a test on another mongodb instance, on 1300 qps 363 iop we used during fsync (every 30 sec).

the major difference between 2 mongos is the db size. IOPS in my mongo seems like an exceptional.

I want to understand how db size impacts write iops during fsync. (In my understanding it should not have).
What other factors are there in fsync write iops?
what data should i be looking at?



 Comments   
Comment by Edwin Zhou [ 20/Oct/20 ]

c.programming.doubts@gmail.com, I'm happy to hear that you were able to resolve the issue. I'll be closing the ticket as requested.

Best,
Edwin

Comment by maneesh bhunwal [ 19/Oct/20 ]

We were able to reproduce the issue on a much smaller data set, hence it seems like a constrain only. I am sorry i can not share any data due to some constrains. Please feel free to close this ticket.

Thanks for spending your time on this.

Comment by Edwin Zhou [ 19/Oct/20 ]

Hi c.programming.doubts@gmail.com,

We still need additional information to diagnose the problem. If this is still an issue for you, would you please archive (tar or zip) the $dbpath/diagnostic.data directory (the contents are described here) and attach it to this ticket?

Thanks,

Edwin

Comment by Edwin Zhou [ 09/Oct/20 ]

Hi c.programming.doubts@gmail.com,

Thanks for the information you provided so far. Would you please archive (tar or zip) the $dbpath/diagnostic.data directory (the contents are described here) and attach it to this ticket?

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