[SERVER-21245] Understanding query routing in tag-aware sharding setup Created: 02/Nov/15  Updated: 02/Nov/15  Resolved: 02/Nov/15

Status: Closed
Project: Core Server
Component/s: None
Affects Version/s: 3.0.4
Fix Version/s: None

Type: Bug Priority: Major - P3
Reporter: Steffen Assignee: Unassigned
Resolution: Done Votes: 0
Labels: None
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

Operating System: ALL
Participants:

 Description   

Setup:
We have a sharding setup with tag-aware sharding and 22 shards. Each shard is a replica set consisting of 2 hosts and a backup replica (3 nodes in repset config)

Issue:
We are facing issues where our mongod process is hitting 100% CPU usage on 1 thread and everything slows down.

Details:
We use tag-aware sharding to spread collections between shards.
Thus we have shards which only have data for specific database/collections.
We wonder, why we see querys (removes and updates) on shards which have no data for this database/collection. (All found in slow query log)
Due to this remove extra querys on 1 of our shards the lock "scheduler" went crazy and CPU usage where at 100% (1 thread) while IOPS and mongod operations got stalled.

1) Is it by design that remove commands are sent to all shards in a cluster even databse/collections doesn't exists on all shards?
2) Why do we see update querys on shards which don't have this database/collection?



 Comments   
Comment by Steffen [ 02/Nov/15 ]

To determine if it's a bug or not we need to know if it works as designed.

Comment by Ramon Fernandez Marina [ 02/Nov/15 ]

Steffen, please note that the SERVER project is for reporting bugs or feature suggestions for the MongoDB server. For MongoDB-related support discussion please post on the mongodb-user group or Stack Overflow with the mongodb tag, where your question will reach a larger audience. A question like this involving more discussion would be best posted on the mongodb-user group. See also our Technical Support page for additional support resources.

Regards,
Ramón.

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