How to migrate mongoDB storage engine from MMAPv1 to WiredTiger in Satellite 6.5 or later?

Environment

• Red Hat Satellite 6.5 and later

Issue

• How to use WiredTiger as the MongoDB storage engine?
• Is it possible to migrate MongoDB storage engine from mmapv1 to WiredTiger?
• What storage engine is used by MongoDB in Satellite 6?

Resolution

It is strongly advised to backup MongoDB before this procedure, esp. on pre-6.7 releases. There are specific scenarios that might lead to empty DB so an extra backup is worth to have.

• Follow steps in this 6.7 documentation, even on older Satellite

For Satellite 6.7.1 or older, apply further these steps:

• To prevent future runs of satellite-installer to refer to MMAPv1-engine remove the following line
  in /etc/foreman-installer/custom-hiera.yaml:

  mongodb::server::storage_engine: 'mmapv1'
  

• After completed, it is recommended that you perform the tuning outlined in the following document to ensure proper memory consumption with the WiredTiger engine:

  • https://access.redhat.com/solutions/4505561

• Additional information:
  • Note that Satellite 6.4 and Satellite 6.5 get WiredTiger storage engine by default on new installations.
  • Currently, the upgrade of storage engine to WiredTiger is supported only on Satellite 6.5. This capability for 6.4 will be available when This content is not included.Bugzilla 1715227 is fixed.
  • Also, This content is not included.RFE BZ 1727926 has been filed to change the directory instead of /var/tmp.

For more KB articles/solutions related to Red Hat Satellite 6.x MongoDB Issues, please refer to the Consolidated Troubleshooting Article for Red Hat Satellite 6.x MongoDB-related Issues

Root Cause

The main reasons for using WiredTiger in favour of mmap1 are the following:

• better locking mechanism that applies more locally, causing concurrent requests to wait less time
• mongodb scales better when adding more CPUs
• smaller disk size is expected

Diagnostic Steps

• How to check storage engine from the command line?

  mongo pulp_database --eval "db.serverStatus().storageEngine"
  

• It returns the storage engine being used currently, For example:

   "name" : "wiredTiger"
  

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