MongoDB tip: Index Consideration/Tips/Limitations

MongoDB Index Consideration and Tips

Insert, delete, update on a collection will update the indexes per transaction.

• Index improved read performance for queries that are supported by the index.
• Index will be slower where there are indexes that MongoDB must also update.
• The speed of updates may be improved because MongoDB will not need to do a collection scan to find target documents.

Index is modified any time when a document:

• is inserted (applies to all indexes)
• is deleted (applies to all indexes)
• is updated in such a way that its indexed field changes

Index limitations:

• 64 indexes per collection
• Should never create as many indexes anywhere close to the upper bound
• Write performance will degrade to unusable at somewhere between 20-30

Index options:

• Sparse
  - sparse index will skip any document that doesn't contain the field specified
  - syntax: db.<collection>.createIndex( {field_name : 1}, {sparse : true})
• Unique
  - unique index will prohibit any document with duplicate value in the key selected for the index
  - syntax: db.<collection>.createIndex( {field_name : 1}, {unique : true})
• Background
  - building index in the background is a non blocking operation whereas the default foreground option is a blocking operation
  - it takes longer to build, takes up more space initially, with less impact, than an index built in the foreground