Development Checklist开发检查表

Data Durability数据持久性

• Ensure that your replica set includes at least three data-bearing voting members and that your write operations use w: majority write concern. 请确保您的副本集至少包括三个带有数据的投票成员，并且您的写入操作使用w: majority写入关注。Three data-bearing voting members are required for replica-set wide data durability.复制集范围内的数据持久性需要三个数据承载投票成员。
• Ensure that all instances use journaling.确保所有实例都使用日志记录。

Schema Design架构设计

Data in MongoDB has a dynamic schema. Collections do not enforce document structure. MongoDB中的数据具有动态模式。集合不强制执行文档结构。This facilitates iterative development and polymorphism. 这有利于迭代开发和多态性。Nevertheless, collections often hold documents with highly homogeneous structures. See Data Modeling Concepts for more information.然而，集合往往保存结构高度同质的文件。有关详细信息，请参阅数据建模概念。

• Determine the set of collections that you will need and the indexes required to support your queries. 确定支持查询所需的集合集和索引。With the exception of the _id index, you must create all indexes explicitly: MongoDB does not automatically create any indexes other than _id.除了_id索引，您必须显式创建所有索引：MongoDB不会自动创建_id以外的任何索引。
• Ensure that your schema design supports your deployment type: if you are planning to use sharded clusters for horizontal scaling, design your schema to include a strong shard key. 确保您的架构设计支持您的部署类型：如果您计划使用分片集群进行水平扩展，请将架构设计为包含强分片键。While you can change your shard key later, it is important to carefully consider your shard key choice to avoid scalability and perfomance issues.虽然稍后可以更改分片键，但重要的是要仔细考虑分片键的选择，以避免可扩展性和性能问题。
• Ensure that your schema design does not rely on indexed arrays that grow in length without bound. 请确保您的架构设计不依赖于长度无限制增长的索引数组。Typically, best performance can be achieved when such indexed arrays have fewer than 1000 elements.通常，当这样的索引数组具有少于1000个元素时，可以实现最佳性能。
• Consider the document size limits when designing your schema. 在设计架构时，请考虑文档大小限制。The BSON Document Size limit is 16MB per document. BSON文档大小限制为每个文档16MB。If you require larger documents, use GridFS.如果您需要更大的文档，请使用GridFS。

Replication复制

• Use an odd number of voting members to ensure that elections proceed successfully. 使用奇数名有投票权的成员以确保选举顺利进行。You can have up to 7 voting members. 您最多可以有7名投票成员。If you have an even number of voting members, and constraints, such as cost, prohibit adding another secondary to be a voting member, you can add an arbiter to ensure an odd number of votes. 如果你有偶数个投票成员，并且成本等限制条件禁止添加另一个次要成员作为投票成员，你可以添加一个仲裁器来确保奇数票。For additional considerations when using an arbiter for a 3-member replica set (P-S-A), see Replica Set Arbiter.有关为3成员副本集（P-S-a）使用仲裁器时的其他注意事项，请参阅副本集仲裁器。
  Note

  For the following MongoDB versions, pv1 increases the likelihood of w:1 rollbacks compared to pv0 (no longer supported in MongoDB 4.0+) for replica sets with arbiters:对于以下MongoDB版本，与带有仲裁器的副本集的pv0（在MongoDB 4.0+中不再支持）相比，pv1增加了w:1回滚的可能性：

  • MongoDB 3.4.1
  • MongoDB 3.4.0
  • MongoDB 3.2.11 or earlier

  See Replica Set Protocol Version.请参阅副本集协议版本。

• Ensure that your secondaries remain up-to-date by using monitoring tools and by specifying appropriate write concern.通过使用监控工具并指定适当的写入关注，确保您的辅助设备保持最新状态。
• Do not use secondary reads to scale overall read throughput. 不要使用辅助读取来扩展总体读取吞吐量。See: Can I use more replica nodes to scale for an overview of read scaling. 请参阅：我是否可以使用更多副本节点进行扩展，以了解读取扩展的概述。For information about secondary reads, see: Read Preference.有关二次读取的信息，请参阅：读取首选项。

Sharding分片

• Ensure that your shard key distributes the load evenly on your shards. 确保分片关键帧将负载均匀分布在分片上。See: Shard Keys for more information.有关详细信息，请参阅：分片键。
• Use targeted operations for workloads that need to scale with the number of shards.对需要随分片数量而扩展的工作负载使用有针对性的操作。
• For MongoDB 3.4 and earlier, read from the primary nodes for non-targeted or broadcast queries as these queries may be sensitive to stale or orphaned data.对于MongoDB 3.4及更早版本，请从主节点读取非目标或广播查询，因为这些查询可能对陈旧或孤立数据敏感。
• For MongoDB 3.6 and later, secondaries no longer return orphaned data unless using read concern "available" (which is the default read concern for reads against secondaries when not associated with causally consistent sessions).对于MongoDB 3.6及更高版本，除非使用"available"读取关注（当与因果一致会话不关联时，这是针对第二方读取的默认读取关注），否则第二方不再返回孤立数据。
  Starting in MongoDB 3.6, all members of the shard replica set maintain chunk metadata, allowing them to filter out orphans when not using "available". 从MongoDB 3.6开始，分片副本集的所有成员都维护chunk元数据，允许他们在不使用"available"时筛选掉孤立项。As such, non-targeted or broadcast queries that are not using "available" can be safely run on any member and will not return orphaned data.因此，不使用"available"的非目标查询或广播查询可以在任何成员上安全运行，并且不会返回孤立数据。
  The "available" read concern can return orphaned documents from secondary members since it does not check for updated chunk metadata. "available"读取关注可以从辅助成员返回孤立文档，因为它不检查更新的区块元数据。However, if the return of orphaned documents is immaterial to an application, the "available" read concern provides the lowest latency reads possible among the various read concerns.但是，如果孤立文档的返回对应用程序来说无关紧要，那么"available"读取关注在各种读取关注中提供了尽可能低的延迟读取。
• Pre-split and manually balance chunks when inserting large data sets into a new non-hashed sharded collection. 在将大型数据集插入新的非哈希分片集合时，预拆分并手动平衡块。Pre-splitting and manually balancing enables the insert load to be distributed among the shards, increasing performance for the initial load.预拆分和手动平衡使插入负载能够在分片之间分布，从而提高初始负载的性能。

Drivers驱动程序

• 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.利用连接池。大多数MongoDB驱动程序都支持连接池。调整连接池大小以适应您的用例，从典型并发数据库请求数的110-115%开始。
• Ensure that your applications handle transient write and read errors during replica set elections.请确保您的应用程序在副本集选择期间处理临时写入和读取错误。
• Ensure that your applications handle failed requests and retry them if applicable. 请确保您的应用程序处理失败的请求，并在适用的情况下重试。Drivers do not automatically retry failed requests.驱动程序不会自动重试失败的请求。
• Use exponential backoff logic for database request retries.对数据库请求重试使用指数退避逻辑。
• Use cursor.maxTimeMS() for reads and wtimeout for writes if you need to cap execution time for database operations.如果需要限制数据库操作的执行时间，请使用cursor.maxTimeMS()进行读取，使用wtimeout进行写入。