Retryable writes allow MongoDB drivers to automatically retry certain write operations a single time if they encounter network errors, or if they cannot find a healthy primary in the replica set or sharded cluster.
Prerequisites
Retryable writes have the following requirements:
- Supported Deployment Topologies
- Retryable writes require a replica set or sharded cluster, and do not support standalone instances.
- Supported Storage Engine
- Retryable writes require a storage engine supporting document-level locking, such as the WiredTiger or in-memory storage engines.
- 3.6+ MongoDB Drivers
Clients require MongoDB drivers updated for MongoDB 3.6 or greater:
Java 3.6+
Python 3.6+
C 1.9+
Go 1.8+
C# 2.5+
Node 3.0+
Ruby 2.5+
Rust 2.1+
Swift 1.2+
Perl 2.0+
PHPC 1.4+
Scala 2.2+
C++ 3.6.6+
- MongoDB Version
- The MongoDB version of every node in the cluster must be
3.6or greater, and thefeatureCompatibilityVersionof each node in the cluster must be3.6or greater. SeesetFeatureCompatibilityVersionfor more information on thefeatureCompatibilityVersionflag. - Write Acknowledgment
- Write operations issued with a Write Concern of
0are not retryable.
Retryable Writes and Multi-Document Transactions
The transaction commit and abort operations are retryable write operations. If the commit operation or the abort operation encounters an error, MongoDB drivers retry the operation a single time regardless of whether retryWrites is set to false.
The write operations inside the transaction are not individually retryable, regardless of value of retryWrites.
For more information on transactions, see Transactions.
Enabling Retryable Writes
- MongoDB Drivers
- Drivers compatible with MongoDB 4.2 and higher enable Retryable Writes by default. Earlier drivers require the
retryWrites=trueoption. TheretryWrites=trueoption can be omitted in applications that use drivers compatible with MongoDB 4.2 and higher.To disable retryable writes, applications that use drivers compatible with MongoDB 4.2 and higher must includeretryWrites=falsein the connection string. mongoshRetryable writes are enabled by default in
mongosh. To disable retryable writes, use the--retryWrites=falsecommand line option:mongosh --retryWrites=false
Retryable Write Operations
The following write operations are retryable when issued with acknowledged write concern; e.g., Write Concern cannot be {w: 0}.
Note
The write operations inside the transactions are not individually retryable.
Methods | Descriptions |
|---|---|
Insert operations | |
Single-document update operations | |
Single document delete operations | |
| |
| Bulk write operations that only consist of the single-document write operations. A retryable bulk operation can include any combination of the specified write operations but cannot include any multi-document write operations, such as |
Bulk write operations that only consist of the single-document write operations. A retryable bulk operation can include any combination of the specified write operations but cannot include any multi-document write operations, such as |
Behavior
Persistent Network Errors
MongoDB retryable writes make only one retry attempt. This helps address transient network errors and replica set elections, but not persistent network errors.
Failover Period
If the driver cannot find a healthy primary in the destination replica set or sharded cluster shard, the drivers wait serverSelectionTimeoutMS milliseconds to determine the new primary before retrying. Retryable writes do not address instances where the failover period exceeds serverSelectionTimeoutMS.
Warning
If the client application becomes temporarily unresponsive for more than the localLogicalSessionTimeoutMinutes after issuing a write operation, there is a chance that when the client applications starts responding (without a restart), the write operation may be retried and applied again.
Diagnostics
The serverStatus command, and its mongosh shell helper db.serverStatus() includes statistics on retryable writes in the transactions section.
Retryable Writes Against local Database
The official MongoDB drivers enable retryable writes by default. Applications which write to the local database will encounter write errors unless retryable writes are explicitly disabled.
To disable retryable writes, specify retryWrites=false in the connection string for the MongoDB cluster.
Error Handling
Starting in MongoDB 6.1, if both the first and second attempt of a retryable write fail without a single write being performed, MongoDB returns an error with the NoWritesPerformed label.
The NoWritesPerformed label differentiates the results of batch operations like insertMany(). In an insertMany operation, one of the following outcomes can occur:
Outcome | MongoDB Output |
|---|---|
No documents are inserted. | Error returned with |
Partial work done. (At least one document is inserted, but not all.) | Error returned without |
All documents are inserted. | Success returned. |
Applications can use the NoWritesPerformed label to definitively determine that no documents were inserted. This error reporting lets the application maintain an accurate state of the database when handling retryable writes.
In previous versions of MongoDB, an error is returned when both the first and second attempts of a retryable write fail. However, there is no distinction made to indicate that no writes were performed.