Retryable Writes可重试写入

Persistent Network Errors持续的网络错误

MongoDB retryable writes make only one retry attempt. MongoDB可重试写入只进行一次重试尝试。This helps address transient network errors and replica set elections, but not persistent network errors.这有助于解决暂时的网络错误和副本集选举，但不会解决持久的网络错误。

Failover Period故障转移周期

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.如果驱动程序在目标副本集中或已分片的集群分片中找不到健康的primary，则驱动程序会等待serverSelectionTimeoutMS毫秒来确定新的主服务器然后重试。可重试写入不会处理故障转移周期超过serverSelectionTimeoutMS的实例。

Duplicate Key Errors on UpsertUpsert上的重复键错误

MongoDB 4.2 will retry single-document upsert operations (i.e upsert : true and multi : false) that fail due to a duplicate key error only if the operation meets all of the following conditions:只有在满足以下所有条件的情况下，MongoDB 4.2才会重试由于重复键错误而失败的单文档追加操作（即upsert : true和multi : false）：

• The target collection has a unique index that caused the duplicate key error.目标集合具有导致重复键错误的唯一索引。
• The update match condition is either:更新匹配条件为：
  • A single equality predicate单个相等谓词

    { "fieldA" : "valueA" },

    or

  • a logical AND of equality predicates相等谓词的逻辑AND

    { "fieldA" : "valueA", "fieldB" : "valueB" }

• The set of fields in the unique index key pattern matches the set of fields in the update query predicate.唯一索引键模式中的字段集与更新查询谓词中的字段集中匹配。
• The update operation does not modify any of the fields in the query predicate.更新操作不会修改查询谓词中的任何字段。

The following table contains examples of upsert operations that the server can or cannot retry on a duplicate key error:下表包含服务器可以或不能在出现重复键错误时重试的追加启动操作示例：

{ _id : 1 }

db.collName.updateOne(
  { _id : ObjectId("1aa1c1efb123f14aaa167aaa") },
  { $set : { fieldA : 25 } },
  { upsert : true }
)

{ fieldA : 1 }

db.collName.updateOne(
  { fieldA : { $in : [ 25 ] } },
  { $set : { fieldB : "someValue" } },
  { upsert : true }
)

{
  fieldA : 1,
  fieldB : 1
}

db.collName.updateOne(
  { fieldA : 25, fieldB : "someValue" },
  { $set : { fieldC : false } },
  { upsert : true }
)

{ fieldA : 1 }

db.collName.updateOne(
  { fieldA : { $lte : 25 } },
  { $set : { fieldC : true } },
  { upsert : true }
)

{ fieldA : 1 }

db.collName.updateOne(
  { fieldA : { $in : [ 25 ] } },
  { $set : { fieldA : 20 } },
  { upsert : true }
)

{ _id : 1 }

db.collName.updateOne(
  { fieldA : { $in : [ 25 ] } },
  { $set : { fieldA : 20 } },
  { upsert : true }
)

{ fieldA : 1 }

db.collName.updateOne(
  { fieldA : 25, fieldC : true },
  { $set : { fieldD : false } },
  { upsert : true }
)

Prior to MongoDB 4.2, MongoDB retryable writes did not support retrying upserts which failed due to duplicate key errors.在MongoDB 4.2之前，MongoDB可重试写入不支持重试由于重复键错误而失败的错误。

Diagnostics诊断

The serverStatus command, and its mongosh shell helper db.serverStatus() includes statistics on retryable writes in the transactions section.serverStatus命令及其mongosh shell助手db.serverStatus()在transactions部分中包含可重试写入的统计信息。

Retryable Writes Against local Database针对local数据库的可重试写入

The official MongoDB 4.2-series drivers enable retryable writes by default. MongoDB 4.2系列的官方驱动程序默认启用可重试写入。Applications which write to the local database will encounter write errors upon upgrading to 4.2-series drivers unless retryable writes are explicitly disabled.写入local数据库的应用程序在升级到4.2系列驱动程序时将遇到写入错误，除非明确禁用了可重试写入。

To disable retryable writes, specify retryWrites=false in the connection string for the MongoDB cluster.要禁用可重试写入，请在MongoDB集群的连接字符串中指定retryWrites=false。

Error Handling错误处理

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.从MongoDB 6.1开始，如果可重试写入的第一次和第二次尝试都失败了，而没有执行一次写入，MongoDB将返回一个带有NoWritesPerformed标签的错误。

The NoWritesPerformed label differentiates the results of batch operations like insertMany(). NoWritesPerformed标签区分insertMany()等批处理操作的结果。In an insertMany operation, one of the following outcomes can occur:在insertMany操作中，可能会出现以下结果之一：

Applications can use the NoWritesPerformed label to definitively determine that no documents were inserted. 应用程序可以使用NoWritesPerformed标签来确定是否未插入任何文档。This error reporting lets the application maintain an accurate state of the database when handling retryable writes.此错误报告使应用程序在处理可重试写入时能够保持数据库的准确状态。

In previous versions of MongoDB, an error is returned when both the first and second attempts of a retryable write fail. 在MongoDB的早期版本中，当可重试写入的第一次和第二次尝试都失败时，会返回一个错误。However, there is no distinction made to indicate that no writes were performed.但是，没有任何区别表明没有执行任何写入操作。