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What checks should I perform before restarting the NuoDB database?

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NuoDB is designed to keep running even with single failures, so restarting a database should be considered a last resort resolution for critical problems.

Checks to perform before bouncing a database:

Check that all nodes are up and connected:

• Run nuocmd show domain
• If a node is listed as UNREACHABLE, then fix that problem first, if at all possible;
  • More information can be found here and here

Check that there are no hung NuoDB processes:

ps -ef | grep nuo

Note: The above command should be executed on all hosts which are dedicated to run NuoDB engine processes.

Check that any inconsistencies in the domain state are addressed:

• For example, any processes that are listed but don’t appear after running ps -ef | grep nuo

Check for any reported errors which would stop the database from starting correctly:

• For example, are there any errors reported by SMs regarding the archives?

Once the database is down, check the archive for consistency

• Use the nuoarchive command with the --repair option.  More information here
• This can be done on an offline copy of the archive if the database needs to be brought up immediately;

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