The following are a few limitations to keep in mind around indexing:

• Index entries have to be <1024 bytes. This is mostly an internal consideration but we can keep it in mind if we run into issues with indexing.
• A collection can have up to 64 indexes.
• A compound index can have up to 31 fields.
• Special indexes cannot be combined in queries. This includes special query operators that have to use special indexes such as $text for text indexes and $near for geospatial indexes. This is because MongoDB can use multiple indexes to fulfill a query but not in all cases. More about this issue in the Index intersection section.
• Multikey and geospatial indexes cannot cover a query. This means that index data alone will not be enough to fulfill the query and the underlying documents will need to be processed by MongoDB to get back the complete set of results.
• Indexes have a unique constraint on fields. We cannot create multiple indexes on the same fields, differing only in options. This is a limitation for sparse and partial indexes, as we cannot create multiple variations of these indexes differing only in the filtering query.