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Development Checklist

Development Checklist¶

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The following checklist, along with the Operations Checklist, provides recommendations to help you avoid issues in your production MongoDB deployment.

Data Durability¶

Ensure that your replica set includes at least three data-bearing nodes with w:majority write concern. Three data-bearing nodes are required for replica-set wide data durability.
Ensure that all instances use journaling.

Schema Design¶

Data in MongoDB has a dynamic schema. Collections do not enforce document structure. This facilitates iterative development and polymorphism. Nevertheless, collections often hold documents with highly homogeneous structures. See Data Modeling Concepts for more information.

Determine the set of collections that you will need and the indexes required to support your queries. With the exception of the _id index, you must create all indexes explicitly: MongoDB does not automatically create any indexes other than _id.
Ensure that your schema design supports your deployment type: if you planning to use sharded clusters for horizontal scaling, design your schema to include a strong shard key. The shard key affects read and write performance by determining how MongoDB partitions data. See: Impacts of Shard Keys on Cluster Operations for information about what qualities a shard key should possess. You cannot change the shard key once it is set.
Ensure that your schema design does not rely on indexed arrays that grow in length without bound. Typically, best performance can be achieved when such indexed arrays have fewer than 1000 elements.
Consider the document size limits when designing your schema. The BSON Document Size limit is 16MB per document. If you require larger documents, use GridFS.

Replication¶

Use an odd number of replica set members to ensure that elections proceed successfully. If you have an even number of members, use an arbiter to ensure an odd number of votes.
Note

For the following MongoDB versions, pv1 increases the likelihood of w:1 rollbacks compared to pv0 for replica sets with arbiters:
- MongoDB 3.4.1
- MongoDB 3.4.0
- MongoDB 3.2.11 or earlier
See Replica Set Protocol Versions.
Ensure that your secondaries remain up-to-date by using monitoring tools and by specifying appropriate write concern.
Do not use secondary reads to scale overall read throughput. See: Can I use more replica nodes to scale for an overview of read scaling. For information about secondary reads, see: Read Preference.

Sharding¶

Ensure that your shard key distributes the load evenly on your shards. See: Shard Keys for more information.
Use targeted operations for workloads that need to scale with the number of shards.
Always read from primary nodes for non-targeted queries that may be sensitive to stale or orphaned data.
Pre-split and manually balance chunks when inserting large data sets into a new non-hashed sharded collection. Pre-splitting and manually balancing enables the insert load to be distributed among the shards, increasing performance for the initial load.

Drivers¶

Make use of connection pooling. Most MongoDB drivers support connection pooling. Adjust the connection pool size to suit your use case, beginning at 110-115% of the typical number of concurrent database requests.
Ensure that your applications handle transient write and read errors during replica set elections.
Ensure that your applications handle failed requests and retry them if applicable. Drivers do not automatically retry failed requests.
Use exponential backoff logic for database request retries.
Use cursor.maxTimeMS() for reads and wtimeout for writes if you need to cap execution time for database operations.

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