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I'm creating a index in mongo:

db.table.createIndex({"chr" : 1, "Start" : 1, "End" : 1, "Ref" : 1, "Alt" : 1})

It runs for some time and gives an error msg:

error in monogdb "errmsg" : "WiredTigerIndex::insert: key too large to index, failing

How do I fix this error?

SiHa
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Anop Singh Ranawat
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  • Hi @anop.perl, can you add some details ? for instance, is the `table` collection already populated ? – danidemi Apr 11 '17 at 10:00
  • Possible duplicate of [Cannot create index in mongodb, "key too large to index"](https://stackoverflow.com/questions/27792706/cannot-create-index-in-mongodb-key-too-large-to-index) – OhadR Jan 08 '19 at 09:23

2 Answers2

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In MongoDB, since 2.6, the total size of an index entry must be less than 1024 bytes. Documentation here

In other terms, at least one of your documents has a large value in one of the field you are trying to index.

It's not a good idea in general to index very large values like that because it creates a big index which is less efficient compared to a smaller one and it takes more space in RAM which could be put to better use on a MongoDB node.

You could use this : mongod --setParameter failIndexKeyTooLong=false.

But it doesn't look like a good idea. If you have a large text to index, you should consider using the Full Text index or you could use a Hashed index.

Maxime Beugnet
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This can also be caused by having both a text index and a standard index for the same field. By deleting one of them you will be able to resolve this issue.

Gabriel Fair
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