Queryable Encryption Limitations
On this page
- Overview
- MongoDB Support Limitations
- Supported Operations
- Manual Metadata Collection Compaction
- Modifying the
encryptedFieldsMap
- The _id Field
- Encrypted Field Names
- Modifying Queryable Fields
- Redaction
- Query Log and Database Profiler Redaction
- Command and Aggregation Stage Output Redaction
- Topology Support
- Sharding
- Collections
- Drop Collection
- Create Collection
- Arrays
- Views
- Collation
- Unique Indexes
Overview
Consider these limitations and restrictions before enabling Queryable Encryption. Some operations are unsupported, and others behave differently.
For compatibility limitations, please read Compatibility.
MongoDB Support Limitations
Enabling Queryable Encryption on a collection redacts fields from some diagnostic commands and omits some operations from the query log. This limits the data available to MongoDB support engineers, especially when analyzing query performance. To measure the impact of operations against encrypted collections, use a third party application performance monitoring tool to collect metrics.
For details, see the Redaction section of this page.
Supported Operations
Queryable Encryption supports a subset of commands, query operators, update operators, aggregation stages, and aggregation expressions. For the list of supported operations, see Supported Operations for Queryable Encryption.
Manual Metadata Collection Compaction
Manually run metadata collection compaction when your metadata collections exceed 1 GB. Compaction decreases the size of the metadata collections associated with encrypted fields, and improves performance.
Modifying the encryptedFieldsMap
Do not modify the encryptedFieldsMap
passed to your MongoClient
. Doing so can
result in unexpected and incorrect behavior when querying.
Queryable Encryption encrypts the set of fields in the encryptedFieldsMap configuration that you pass to your
MongoClient
constructor. If you specify a formerly plaintext field in your
encryptedFieldsMap
configuration that exists in the collection documents, you can only
query on that field for documents inserted after you updated your encryptedFieldsMap
configuration.
For example, consider a database in which you have inserted documents with a
plaintext streetAddress
field. Adding this field to encryptedFieldsMap
and performing
subsequent inserts will insert the encrypted value of streetAddress
into
the database. The driver will send future queries for a specific
streetAddress
as BinData
. As a result, the
plaintext values in the original documents will never match future queries.
The _id Field
You cannot configure Queryable Encryption to encrypt the _id
field because it relies on
the value auto-generated by MongoDB.
Encrypted Field Names
You can't rename an encrypted field. For example, if you specify ssn
as a field to encrypt, you can't $rename
the field name to
taxPayerID
.
Modifying Queryable Fields
The query type you specify for a field when creating the collection in
encryptedFieldsMap
is immutable. You cannot enable new query types to an existing field,
and you cannot change the existing query type.
Redaction
To improve security, Queryable Encryption redacts fields from some diagnostic commands on encrypted collections, and omits certain operations
from the query log. An encrypted collection is any collection with the
encryptedFields
option.
Query Log and Database Profiler Redaction
The CRUD operations below are omitted from the slow operations query log and the Database Profiler system.profile
collection when you run them on an encrypted collection.
The
compactStructuredEncryptionData
commandThe
cleanupStructuredEncryptionData
command
Command and Aggregation Stage Output Redaction
The collStats
command and $collStats
aggregation stage:
Omit
"queryExecStats"
Omit
"latencyStats"
Redact
"WiredTiger"
, if present, to include only theurl
field.
The currentOp
command and $currentOp
aggregation stage:
Omit all fields after
"command"
.Redact
"command"
to include only the first element,$comment
, and$db
.
The top
command only returns the collection name of
encrypted collections.
The $planCacheStats
aggregation stage omits
operations against encrypted collections, even though the operations are cached as normal.
Topology Support
Replica sets and sharded clusters are supported
Standalone deployments are not supported
Secondary reads are not supported
Sharding
Metadata collections must not be sharded
Shard keys must not be encrypted fields
Collections
You cannot use Client-Side Field Level Encryption with Queryable Encryption on the same collection.
Queryable Encryption does not support migration from collections encrypted with Client-Side Field Level Encryption. You must decrypt your documents and insert them one-by-one.
Queryable Encryption does not support automatic migration from an unencrypted collection. You must insert the documents one-by-one.
Queryable Encryption supports new collections only. You cannot add or remove Queryable Encryption to existing collections.
You cannot rename a collection with encrypted fields.
You cannot specify
jsonSchema
todb.createCollection()
when creating a Queryable Encryption collection if thejsonSchema
contains theencrypt
keyword.You can specify both
encryptedFields
andjsonSchema
todb.createCollection()
as long as your jsonSchema does not contain validation for encrypted fields.
Queryable Encryption does not support Views, Time Series Collections, or capped collection.
Queryable Encryption does not support TTL Indexes or Unique Indexes.
You cannot disable
jsonSchema
validation.When a collection uses the
encryptedFields
option:You cannot set
validationLevel
tonone
.You cannot set
validationAction
towarn
.
Drop Collection
Dropping collections from a
MongoClient
that is not configured for Queryable Encryption doesn't drop the associated metadata collections.mongod
logs a warning if you drop a collection with encrypted fields before dropping the metadata collections.
Tip
When dropping a collection with a MongoClient
configured for
Queryable Encryption, compatible drivers drop the associated metadata
collections as well.
Create Collection
Always explicitly create any collections that use Queryable Encryption. Implicit collection creation doesn't create the necessary indexes and metadata collections, resulting in poor query performance.
Arrays
Queryable Encryption does not support automatic encryption on fields within an array of documents.
Views
Applications cannot rely on the automatic encryption validation to prevent unsupported queries against views on collections with encrypted fields.
Queries against views on collections containing values encrypted with Queryable Encryption may return unexpected or incorrect results if either the underlying view aggregation pipeline or the query references encrypted fields. If creating a view on a collection containing values encrypted with Queryable Encryption, avoid operating on encrypted fields to mitigate the risk of unexpected or incorrect results.
For more information on views, see Views.
Collation
Queryable Encryption ignores user-specified collations or collection default collations. Encryption obscures the field value and prevents normal collation behavior. Collation-sensitive queries against encrypted fields may return unexpected or incorrect results.
For more information on collations, see Collation Document.
Queryable Encryption-compatible drivers have a list of supported operations for automatic encryption. For unsupported read and write operations, the underlying support library cannot introspect the collection catalog to identify the default collation. Applications therefore cannot rely on the Queryable Encryption validation to prevent querying on encrypted fields with collation defaults.
Unique Indexes
Unique indexes can't guarantee uniqueness if the index key specifies any encrypted fields.
Queryable Encryption always outputs a different encrypted value, even for the same input. The server considers each encrypted value unique, even though the decrypted value may not be. This means that even if a collection uses an index-enforced unique constraint on fields, the collection can still contain multiple documents with duplicate plaintext values for that field.
Queryable Encryption compatible drivers configured for automatic encryption support some operations for automatic encryption. For unsupported read and write operations, the underlying library can't introspect the index catalog to identify a given field as unique. Applications can't rely on automatic encryption validation to prevent unique constraint violations on randomly-encrypted fields.