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mongodbindexingfiltered-indexpartial-index

What are the limitations of partial indexes?

The latest version of MongoDB (v3.2) adds support for partial (filtered) indexes. You supply a filter when you create the index and that filter determines which documents will be referenced in the index and which will not.

Can I use any filter expression (as long as it's a valid filter)? Or are there limitations to the filter being used? If so, what are those limitations?

Solution

  • Can I use any filter expression?

    No, partial indexes support only a subset of the operators in the filter used. The only supported operators are: $AND (only at the top level), $EQ, $LT, $LTE, $GT, $GTE, $EXISTS and the TYPE_OPERATOR.

    That leaves out, for example $NOT, $REGEX, $OR, etc.

    You can see that in the source for MongoDB here.

    What are those limitations?

    There are also some general limitations on partial indexes:

    • _id indexes can't be partial indexes.
    • Sparse indexes can't be partial indexes.
    • Shard key indexes can't be partial indexes.
    • Partial indexes aren't supported in versions earlier than 3.2.