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- Sharded Cluster Tutorials >
- Troubleshoot Sharded Clusters
Troubleshoot Sharded Clusters¶
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This section describes common strategies for troubleshooting sharded cluster deployments.
Config Database String Error¶
Start all mongos
instances in a sharded cluster with an identical
configDB
string. If a mongos
instance tries to
connect to the sharded cluster with a configDB
string that
does not exactly match the string used by the other mongos
instances, including the order of the hosts, the following errors occur:
And:
To solve the issue, restart the mongos
with the correct
string.
Cursor Fails Because of Stale Config Data¶
A query returns the following warning when one or more of the
mongos
instances has not yet updated its cache of the
cluster’s metadata from the config database:
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
flushRouterConfig
command.
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.