MongoDB could not restore backup because of “key too large to index” error

Robert ReizMay 3, 2014May 3, 2014UncategorizedMongoDB

Recently I made a db dump on a MongoDB 2.4 server like this:

mongodump --db veye_dev

And I tried to restore it on a MongoDB 2.6 server like this:

mongorestore dump/veye_dev

Unfortunately at some point the restore process failed with this error message:

mongo error: "Btree::insert: key too large to index, failing

There are some restrictions for the size of the index in MongoDB 2.6. Luckily I found the issue on MongoDBs ticket system. The import can succeed if the mongod process is running with the parameter “failIndexKeyTooLong=false”. Just start it like that:

sudo mongod --setParameter failIndexKeyTooLong=false

And now execute the mongorestore again. That worked for me.

Published by Robert Reiz

CEO @ VersionEye. Passionated software developer since 1998. View more posts

7 thoughts on “MongoDB could not restore backup because of “key too large to index” error”

Sam says:

June 8, 2014 at 9:44 AM

This just bit me too. I also discovered that you can set that flag on a running mongod instance, with:

db.getSiblingDB(‘admin’).runCommand( { setParameter: 1, failIndexKeyTooLong: false } )

Reply
1. Robert Reiz says:
  
  June 8, 2014 at 2:55 PM
  
  Thanks for the hint. That’s useful. I had to restart my MongoDB instance.
  
  Reply
Goal Lin says:

June 28, 2014 at 10:52 AM

Thanks for your article, this save me a lot of time.

Reply
sachin says:

September 22, 2014 at 10:32 PM

thanks for such nice answer. Worked for me.

Reply
kommrad homer says:

February 13, 2015 at 9:17 AM

you should also note that this document won’t show up on searches anymore

Reply
kommradhomer says:

February 13, 2015 at 9:18 AM

you should also not that , those documents are not indexed and they won’t show up on searches

Reply
Jae Min Kim says:

March 12, 2015 at 8:12 AM

Thanks for article. but, Non-indexed data is not the search. What should I do?

Reply