[SERVER-13510] mongos performance issue Created: 08/Apr/14  Updated: 10/Dec/14  Resolved: 02/Jun/14

Status: Closed
Project: Core Server
Component/s: Performance, Sharding
Affects Version/s: 2.4.5
Fix Version/s: None

Type: Question Priority: Major - P3
Reporter: David Wang Assignee: Ramon Fernandez Marina
Resolution: Done Votes: 0
Labels: None
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

Participants:

 Description   

data model like this:

{gen_id: 1234, other: data}

the data is stored on 5 shards, the gen_id is the shard key,and is not unique.

the problem is i found that if i send exactly the SAME query many times, the first query is always slow.
gen_id=118832718, Object Returned = 21, Time = 184.354139ms
gen_id=118832718, Object Returned = 21, Time = 2.165057ms
gen_id=118832718, Object Returned = 21, Time = 1.814072ms
gen_id=118832718, Object Returned = 21, Time = 1.639094ms

the pageFaultExceptionsThrown and accessesNotInMemory counter didn't change, so it's not likely because of page faults.
And if i query the 5 shards directly, the numbers are close to 2-5ms.

can anyone suggest and help me? Or dose the mongos need warm-up?



 Comments   
Comment by Ramon Fernandez Marina [ 02/Jun/14 ]

Hi David,

I haven’t heard back from you for some time, so I’m going to mark this ticket as resolved. If this is still an issue for you, feel free to re-open the ticket and provide additional information.

Regards,
Ramón.

Comment by Ramon Fernandez Marina [ 16/May/14 ]

Hi David,

we haven't heard from you in a while. If this is still an issue for you, can you please provide the information requested in the previous comment to help us diagnose this behavior?

Thanks,
Ramón.

Comment by Ramon Fernandez Marina [ 01/May/14 ]

Hi David,

in order to diagnose this behavior we're going to need some more information:

  1. Can you please elaborate on the meaning on "the first query" above? Does this happen on the first query on each collection? Or after some kind of reboot/restart?
  2. Can you send us the exact query that you're running?
  3. Can you repeat the scenario above with logLevel increased to 3 and send us the resulting logs? The hypothesis we're working with is that the mongos need to refresh the metadata from the config servers on that "first query", and detailed logs should tell us whether that's the case or not.

Regards,
Ramón.

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