Troubleshoot Sharded Clusters¶
On this page
- Application Servers or
mongosInstances Become Unavailable
- A Single
mongodBecomes Unavailable in a Shard
- All Members of a Shard Become Unavailable
- A Config Server Replica Set Member Become Unavailable
- Cursor Fails Because of Stale Config Data
- Shard Keys and Cluster Availability
- Config Database String Error
- Avoid Downtime when Moving Config Servers
moveChunk commit failedError
This page describes common strategies for troubleshooting sharded cluster deployments.
Cursor Fails Because of Stale Config Data¶
could not initialize cursor across all shards because : stale config detected
This warning should not propagate back to your application. The
warning will repeat until all the
mongos instances refresh
their caches. To force an instance to refresh its cache, run the
Config Database String Error¶
Changed in version 3.2.
Starting in MongoDB 3.2, config servers can be deployed as replica
mongos instances for the sharded cluster must
specify the same config server replica set name but can specify
hostname and port of different members of the replica set.
Starting in 3.4, the use of the deprecated mirrored
instances as config servers (SCCC) is no longer supported. Before you
can upgrade your sharded clusters to 3.4, you must convert your config
servers from SCCC to CSRS.
To convert your config servers from SCCC to CSRS, see Upgrade Config Servers to Replica Set.
With earlier versions of MongoDB sharded clusters that use the topology
of three mirrored
mongod instances for config servers,
mongos instances in a sharded cluster must specify identical
Avoid Downtime when Moving Config Servers¶
Use CNAMEs to identify your config servers to the cluster so that you can rename and renumber your config servers without downtime.
moveChunk commit failed Error¶
At the end of a chunk migration, the shard must connect to the config database to update the chunk’s record in the cluster metadata. If the shard fails to connect to the config database, MongoDB reports the following error:
ERROR: moveChunk commit failed: version is at <n>|<nn> instead of <N>|<NN>" and "ERROR: TERMINATING"
When this happens, the primary member of the shard’s replica set then terminates to protect data consistency. If a secondary member can access the config database, data on the shard becomes accessible again after an election.