How to handle the new MongoDB warnings


A new check on MongoDB databases on Compose will reveal if you've placed data in a bad place. In this article, we'll show you how to get it to the good place.

If you have a MongoDB database, you may be seeing this warning on the overview - Warning: Found unexpected data stored in admin database.

Found unexpected data in admin screenshot

If you aren't seeing the warning, good news, you aren't affected and your data is already in the good place. If you haven't checked your MongoDB's overview on the web recently, we recommend you check it. If you see this message, read on.

We've written in the past about the dangers of leaving data in the admin database within MongoDB. The short version is that it is not somwhere you want to keep data. The admin database is an auxiliary database within MongoDB for, as the name suggests, administration and it should only hold admin user credentials and some metadata. Keeping your actual data in there is bad practice, it's bad for performance and bad for reliability.

We recommend you move it out as soon as possible and make sure your applications aren't writing there.

Finding out what's in there

Create yourself an admin level user, if you haven't already. You can do this through the Compose console's browser by accessing the admin database. Users created here get almost complete control of the database. You'll notice you can't see any collections in the Compose console browser for the admin collection - you'll have to log in with mongo shell to continue. You can find an example command line on the Compose console overview for your database. Just replace the values after -u and -p with your user's username and password. Then log in:

MongoDB shell version v3.4.9  
connecting to: mongodb://  
MongoDB server version: 3.2.10  
WARNING: shell and server versions do not match  

Once logged in, ask to use the admin database.

mongos> use admin  
switched to db admin  

And then list the collections saved in the admin database using db.getCollectionNames():

mongos> db.getCollectionNames()  
[ "system.users", "system.version", "words" ]

And there's the troublemaker. The system. collections are meant to be there but someone's created a words collection in admin.

Is the collection used?

In our example, we know our words collection isn't used and we could fix the warning by simply dropping the collection. Non-system collections in admin aren't backed up so you'll want to be completely sure that the collection or collections are not used before doing this. There is no way back. You may have an application that is relying on this collection, so before you commit to it, let's make a copy of the data.

Copying a collection

We're going to make a copy of the collection. To assist in this, we are also providing a script, which breaks out all the settings. If you browse the MongoDB documentation, you'll find a number of functions for copying collections. Unfortunately they either don't work with a sharded MongoDB or mongos, as provided on Compose, or they are deprecated because they bring the database to a halt while the copying takes place. So, what we have here is a script which uses mongoexport to export a collection from admin. It then pipes the results straight into mongoimport which writes it to a new collection in the compose database.

# MONGOHOST is the host the database is accessible on - include hostname and port
# COLLECTION is the name of the collection we want to copy from in the admin database
export COLLECTION=words  
# NEWCOLLECTION is the name of the collection we want to create in the compose database
export NEWCOLLECTION=wordstoo  
# MONGOCREDENTIALS is the settings for user, password and authentication database 
# where that user can be found - note this should be a user in the admin database with
# sufficient privileges to access both collections in each database.
export MONGOCREDENTIALS="-u username -p password --authenticationDatabase admin"  
# SSLPARAMS enables SSL with no certificate verification - leave empty for no SSL
export SSLPARAMS="--ssl --sslAllowInvalidCertificates"  
# This command now exports from admin.$COLLECTION and writes it to compose.$NEWCOLLECTION
# It does not delete the original collection in admin
mongoexport $SSLPARAMS --host $MONGOHOST $MONGOCREDENTIALS --db admin --collection $COLLECTION | mongoimport $SSLPARAMS --host $MONGOHOST $MONGOCREDENTIALS --db compose --collection $NEWCOLLECTION  

All you need to do is pop in the correct host and port in MONGOHOST, name of the collection you want to copy from (COLLECTION), name of the new collection to be created (NEWCOLLECTION) and substitute in your administration user and password in MONGOCREDENTIALS. Then run the script

2017-12-11T12:10:51.846+0000    connected to:  
2017-12-11T12:10:51.985+0000    connected to:  
2017-12-11T12:10:52.074+0000    exported 3 records  
2017-12-11T12:10:52.765+0000    imported 3 documents  

If we now log in on the command line, we can see our new collection:

mongos> use compose  
switched to db compose  
mongos> db.getCollectionNames()  
[ "wordstoo" ]

And, after checking everything is fine, go back to the admin database and drop the old collection.

mongos> use admin  
switched to db admin  
mongos> db.words.drop()  

There will be a delay between this being done and the warning in the Compose console going away due to the way this check is performed. You'll have to wait up to an hour before the warning clears from the Compose UI and API.

Safety first

Once those collections have been dropped, do check back after a day or so to ensure none of your applications are still creating collections in the admin database. If they are, you'll need to correct their connection code and, for safety, explicitly use the drivers implementation of use databasename to address the right, non-admin database.

The important thing to take away from this process is that moving your collections out of the admin database means your data will be safe and in the right part of MongoDB. That also means your data is then being backed up correctly and performing optimally. Take note of the warning and act on it today to protect your data.

Read more articles about Compose databases - use our Curated Collections Guide for articles on each database type. If you have any feedback about this or any other Compose article, drop the Compose Articles team a line at We're happy to hear from you.

attribution Ash from Modern Afflatus

Dj Walker-Morgan
Dj Walker-Morgan was Compose's resident Content Curator, and has been both a developer and writer since Apples came in II flavors and Commodores had Pets. Love this article? Head over to Dj Walker-Morgan’s author page to keep reading.

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