Database Manual / Sharding / Reference

Config Database配置数据库

The collections in the config database support:config数据库中的集合支持：

Note

Sharded clusters may show different collections in the config database, depending on whether you connect to mongos or mongod:分片集群可能会在config数据库中显示不同的集合，具体取决于您是连接到mongos还是mongod：

When a config server and a shard are hosted on the same node, mongos may have access to some shard-local collections in the config database.当配置服务器和分片托管在同一节点上时，mongos可能可以访问config数据库中的一些分片本地集合。

Restrictions限制

Starting in MongoDB 5.0, non-transaction reads are not allowed on the config.transactions collection with the following read concerns and options:从MongoDB 5.0开始，不允许对config.transactions集合进行非事务读取，具有以下读取关注和选项：

Important

The schema of the config database is internal and may change between releases of MongoDB. config数据库的模式是内部的，可能会在MongoDB的不同版本之间发生变化。The config database is not a dependable API, and users should not write data to the config database in the course of normal operation or maintenance.config数据库不是一个可靠的API，用户在正常运行或维护过程中不应将数据写入config数据库。

Note

You cannot perform read/write operations to the collections in the config database inside a multi-document transaction.您不能在多文档事务中对config数据库中的集合执行读/写操作。

Collections to Support Sharded Cluster Operations支持分片集群操作的集合

To access the config database and view the list of collections that support sharding operations, connect mongosh to a mongos instance in a sharded cluster and issue the following:要访问配置数据库并查看支持分片操作的集合列表，请将mongosh连接到分片集群中的mongos实例，然后发出以下命令：

use config

show collections

Note

If running with access control, ensure you have privileges that grant listCollections action on the database.如果使用访问控制运行，请确保您具有在数据库上授予listCollections操作的权限。

The config database is mainly for internal use, and during normal operations you should never manually insert or store data in it. However, if you need to verify the write availability of the config server for a sharded cluster, you can insert a document into a test collection (after making sure that no collection of that name already exists):配置数据库主要供内部使用，在正常操作期间，您不应手动在其中插入或存储数据。但是，如果您需要验证分片集群的配置服务器的写可用性，您可以将文档插入测试集合中（在确保该名称的集合不存在之后）：

Warning

Modification of the config database on a functioning system may lead to instability or inconsistent data sets. 修改功能系统上的config数据库可能会导致数据集不稳定或不一致。If you must modify the config database, use mongodump to create a full backup of the config database.如果必须修改config数据库，请使用mongodump创建配置数据库的完整备份。

db.testConfigServerWriteAvail.insertOne( { a : 1 } )

If the operation succeeds, the config server is available to process writes.如果操作成功，则配置服务器可用于处理写入。

Future releases of the server may include different collections in the config database, so be careful when selecting a name for your test collection.服务器的未来版本可能会在配置数据库中包含不同的集合，因此在为测试集合选择名称时要小心。

MongoDB uses the following collections in the config database to support sharding:MongoDB在config数据库中使用以下集合来支持分片：

config.changelog

Tip

Internal MongoDB Metadata内部MongoDB元数据

The config database is internal. Applications and administrators should not modify or depend on its content during normal operation.config数据库是内部的。在正常运行期间，应用程序和管理员不应修改或依赖其内容。

The changelog collection stores a document for each change to the metadata of a sharded collection.changelog集合为分片集合的元数据的每次更改存储一个文档。

Example示例

The following example displays a single record of a chunk split from a changelog collection:以下示例显示了从changelog集合中分割的块的单个记录：

{
 "_id" : "<hostname>-<timestamp>-<increment>",
 "server" : "<hostname><:port>",
 "clientAddr" : "127.0.0.1:63381",
 "time" : ISODate("2012-12-11T14:09:21.039Z"),
 "what" : "split",
 "ns" : "<database>.<collection>",
 "details" : {
    "before" : {
       "min" : {
          "<database>" : { $minKey : 1 }
       },
       "max" : {
          "<database>" : { $maxKey : 1 }
       },
       "lastmod" : Timestamp(1000, 0),
       "lastmodEpoch" : ObjectId("000000000000000000000000")
    },
    "left" : {
       "min" : {
          "<database>" : { $minKey : 1 }
       },
       "max" : {
          "<database>" : "<value>"
       },
       "lastmod" : Timestamp(1000, 1),
       "lastmodEpoch" : ObjectId(<...>)
    },
    "right" : {
       "min" : {
          "<database>" : "<value>"
       },
       "max" : {
          "<database>" : { $maxKey : 1 }
       },
       "lastmod" : Timestamp(1000, 2),
       "lastmodEpoch" : ObjectId("<...>")
    },
    "owningShard" : "<value>"
 }
}

Each document in the changelog collection contains the following fields:changelog集合中的每个文档都包含以下字段：

config.changelog._id
The value of changelog._id is: <hostname>-<timestamp>-<increment>.changelog._id的值是：<hostname>-<timestamp>-<increment>。
config.changelog.server
The hostname of the server that holds this data.保存此数据的服务器的主机名。
config.changelog.clientAddr
A string that holds the address of the client, a mongos instance that initiates this change.一个包含客户端地址的字符串，一个启动此更改的mongos实例。
config.changelog.time
A ISODate timestamp that reflects when the change occurred.反映更改发生时间的ISODate时间戳。
config.changelog.what

The type of change recorded. Possible values include:记录的更改类型。可能的值包括：

  • dropCollection
  • dropCollection.start
  • dropDatabase
  • dropDatabase.start
  • moveChunk.start
  • moveChunk.commit
  • split
  • multi-split
config.changelog.ns
Namespace where the change occurred.发生更改的命名空间。
config.changelog.details
A document that contains additional details for the change. The structure of the details document depends on the type of change.包含更改的其他详细信息的文档。details文档的结构取决于更改的类型。
config.chunks

Tip

Internal MongoDB Metadata内部MongoDB元数据

The config database is internal. Applications and administrators should not modify or depend on its content during normal operation.config数据库是内部的。在正常运行期间，应用程序和管理员不应修改或依赖其内容。

The config.chunks collection stores a document for each chunk in the cluster. The following example shows a document:config.chunks集合为集群中的每个块存储一个文档。以下示例显示了一个文档：

{
   _id: ObjectId('65a954c0de11596e08e7c1dc'),
   uuid: UUID('a4479215-a38d-478f-a82b-e5e95d455e55'),
   min: { a: Long('121204345') },
   max: { a: Long('993849349') },
   shard: 'shard01',
   lastmod: Timestamp({ t: 1, i: 0 }),
   history: [
      {
         validAfter: Timestamp({ t: 1705596095, i: 14 }),
         shard: 'shard01'
      }
   ]
}

In the document:在文件中：

  • _id is the chunk identifier.是块标识符。
  • min and max are the range of values for the chunk's shard key.min和max是块的分片键的值范围。
  • shard is the name of the shard that stores the chunk in the cluster.是集群中存储块的分片的名称。

Tip

To find the chunks in a collection, retrieve the collection's uuid identifier from the config.collections collection. 要查找集合中的块，请从config.collections集合中检索该集合的uuid标识符。Then, use uuid to retrieve the matching document with the same uuid from the config.chunks collection.然后，使用uuid从config.chunks集合中检索具有相同uuid的匹配文档。

config.collections

Tip

Internal MongoDB Metadata内部MongoDB元数据

The config database is internal. Applications and administrators should not modify or depend on its content during normal operation.config数据库是内部的。在正常运行期间，应用程序和管理员不应修改或依赖其内容。

Starting in MongoDB 8.0, config.collections stores metadata for all sharded collections and unsharded collections moved with moveCollection.从MongoDB 8.0开始，config.collections存储所有分片集合和使用moveCollection移动的未分片集合的元数据。

In MongoDB versions earlier than 8.0, config.collections only stores metadata for sharded collections.在早于8.0的MongoDB版本中，config.collections仅存储分片集合的元数据。

config.collections only stores metadata about collections, not the documents stored in the collections.仅存储关于集合的元数据，而不存储集合中存储的文档。

For a collection named pets in the records database, a document in the collections collection would resemble the following:对于records数据库中名为pets的集合，collections集合中的文档类似于以下内容：

{
   "_id" : "records.pets",
   "lastmod" : ISODate("2021-07-21T15:48:15.193Z"),
   "timestamp": Timestamp(1626882495, 1),
   "key" : {
         "a" : 1
   },
   "unique" : false,
   "lastmodEpoch" : ObjectId("5078407bd58b175c5c225fdc"),
   "uuid" :  UUID("f8669e52-5c1b-4ea2-bbdc-a00189b341da")
}
config.csrs.indexes

New in version 7.0.在版本7.0中新增。

Tip

Internal MongoDB Metadata内部MongoDB元数据

The config database is internal. Applications and administrators should not modify or depend on its content during normal operation.config数据库是内部的。在正常运行期间，应用程序和管理员不应修改或依赖其内容。

The indexes collection stores a document for each global index available on a shard.indexes集合为分片上可用的每个全局索引存储一个文档。

Each document in the collection contains the following fields:集合中的每个文档都包含以下字段：

Field字段Data TypeDescription描述
nameString字符串Name of the global index.全局索引的名称。
keyPatternDocument文档Index key specification.索引键规格。
optionsDocument文档Provides information on specified index options, including whether the index is a global index.提供有关指定索引选项的信息，包括索引是否为全局索引。
lastmodTimestampTimestamp that provides information on when the index was last modified and the index version.时间戳，提供有关索引上次修改时间和索引版本的信息。
collectionUUIDUUIDUUID of the sharded collection.分片集合的UUID。
indexCollectionUUIDUUIDUUID of the secondary collection that tracks the global index.跟踪全局索引的辅助集合的UUID。
config.databases

Tip

Internal MongoDB Metadata内部MongoDB元数据

The config database is internal. Applications and administrators should not modify or depend on its content during normal operation.config数据库是内部的。在正常运行期间，应用程序和管理员不应修改或依赖其内容。

The databases collection stores a document for each database in the cluster.databases集合为集群中的每个数据库存储一个文档。

For each database, the corresponding document displays the name, the database's primary shard , and a version.对于每个数据库，相应的文档显示名称、数据库的主分片和版本。

{ "_id" : "test", "primary" : "shardA", "version" : { "uuid" : UUID("516a5f79-5eb9-4844-8ee9-b8e9de91b760"), "timestamp" : Timestamp(1626894204, 1), "lastMod" : 1 } }
{ "_id" : "hr", "primary" : "shardA", "version" : { "uuid" : UUID("8e39d61d-6259-4c33-a5ed-bcd2ae317b6f"), "timestamp" : Timestamp(1626895015, 1), "lastMod" : 1 } }
{ "_id" : "reporting", "primary" : "shardB", "version" : { "uuid" : UUID("07c63242-51b3-460c-865f-a67b3372d792"), "timestamp" : Timestamp(1626895826, 1), "lastMod" : 1 } }

The method sh.status() returns this information in the Databases section.

config.migrationCoordinators

The migrationCoordinators collection exists on each shard and stores a document for each in-progress chunk migration from this shard to another shard. The chunk migration fails if the document cannot be written to a majority of the members of the shard's replica set.

When a migration is complete, the document describing the migration is deleted from the collection.

config.mongos

Tip

Internal MongoDB Metadata

The config database is internal. Applications and administrators should not modify or depend on its content during normal operation.

The mongos collection stores a document for each mongos instance affiliated with the cluster. The cluster maintains this collection for reporting purposes.

Each document in the mongos collection contains these fields:

Field字段Data TypeDescription描述
_idString字符串The hostname and port where the mongos is running. The _id is formatted as <hostname>:<port>.
advisoryHostFQDNsArray of stringsArray of the mongos's fully qualified domain names (FQDNs).
createdDate

When the mongos was started.

New in version 5.2.在版本5.2中新增。

mongoVersionString字符串Version of MongoDB that the mongos is running.
pingDatemongos instances send pings to the config server every 30 seconds. This field indicates the last ping time.
upNumberLongNumber of seconds the mongos has been up as of the last ping.
waitingBoolean布尔值This field is always true and is only included for backward compatibility.

The following document shows the status of the mongos running on example.com:27017.

[
   {
     _id: 'example.com:27017',
     advisoryHostFQDNs: [ "example.com" ],
     created: ISODate("2021-11-22T16:32:13.708Z"),
     mongoVersion: "5.2.0",
     ping: ISODate("2021-12-15T22:09:23.161Z"),
     up: Long("2007429"),
     waiting: true
   }
]
config.rangeDeletions

The rangeDeletions collection exists on each shard and stores a document for each chunk range that contains orphaned documents. The chunk migration fails if the document cannot be written to a majority of the members of the shard's replica set.

When the orphaned chunk range is cleaned up, the document describing the range is deleted from the collection.

config.settings

Tip

Internal MongoDB Metadata

The config database is internal. Applications and administrators should not modify or depend on its content during normal operation.

The settings collection holds the following sharding configuration settings:

  • Range size. To change range size, see Modify Range Size in a Sharded Cluster. The specified chunksize value is in megabytes.
  • Balancer settings. To change the balancer settings, including balancer status, see Manage Sharded Cluster Balancer.

  • Autosplit:

    Starting in MongoDB 6.0.3, automatic chunk splitting is not performed. This is because of balancing policy improvements. Auto-splitting commands still exist, but do not perform an operation.

    In MongoDB versions earlier than 6.1:

Example documents in the settings collection:

{ "_id" : "chunksize", "value" : 64 }
{ "_id" : "balancer", "mode" : "full", "stopped" : false }
config.shards

Tip

Internal MongoDB Metadata

The config database is internal. Applications and administrators should not modify or depend on its content during normal operation.

The shards collection represents each shard in the cluster in a separate document, as in the following:

{ "_id" : "shard0000", "host" : "localhost:30000", "state" : 1 }

If the shard is a replica set, the host field displays the name of the replica set, then a slash, then a comma-separated list of the hostnames of each member of the replica set, as in the following example:

{ "_id" : "shard0001", "host" : "shard0001/localhost:27018,localhost:27019,localhost:27020", "state" : 1 }

If the shard has zones assigned, this document has a tags field, that holds an array of the zones to which it is assigned, as in the following example:

{ "_id" : "shard0002", "host" : "localhost:30002", "state" : 1, "tags": [ "NYC" ] }
config.tags

Tip

Internal MongoDB Metadata

The config database is internal. Applications and administrators should not modify or depend on its content during normal operation.

The tags collection holds documents for each zone range in the cluster. The documents in the tags collection resemble the following:

{
    "_id" : { "ns" : "records.users", "min" : { "zipcode" : "10001" } },
    "ns" : "records.users",
    "min" : { "zipcode" : "10001" },
    "max" : { "zipcode" : "10281" },
    "tag" : "NYC"
}
config.version

Tip

Internal MongoDB Metadata内部MongoDB元数据

The config database is internal. Applications and administrators should not modify or depend on its content during normal operation.config数据库是内部的。在正常运行期间，应用程序和管理员不应修改或依赖其内容。

The version collection holds the current metadata version number. This collection contains only one document. For example:

{ "_id" : 1, "minCompatibleVersion" : 5, "currentVersion" : 6, "clusterId" : ObjectId("5d8bc01a690d8abbd2014ddd") }

To access the version collection, you must use the db.getCollection() method. For example, to retrieve the collection's document:

db.getCollection("version").find()

Collections to Support Sessions

The config database contains the internal collections to support causally consistent sessions for standalones, replica sets, and sharded clusters and retryable writes and transactions for replica sets and sharded clusters.

Warning

Do not manually modify or drop these collections.请勿手动修改或删除这些集合。

To access these collections for a mongod or mongos instance, connect mongosh to the instance.

config.system.sessions

The system.sessions collection stores session records that are available to all members of the deployment.

When a user creates a session on a mongod or mongos instance, the record of the session initially exists only in-memory on the instance. Periodically, the instance will sync its cached sessions to the system.sessions collection; at which time, they are visible to all members of the deployment.

To view records in the system.sessions collection, use $listSessions.

Warning

Do not manually modify or drop the system.sessions collection.

In a sharded cluster, the system.sessions collection is sharded.在分片集群中，system.sessions集合是分片的。

When adding a shard to the sharded cluster, if the shard to add already contains its own system.sessions collection, MongoDB drops the new shard's system.sessions collection during the add process.当向分片集群添加分片时，如果要添加的分片已经包含自己的system.sessions集合，MongoDB会在添加过程中删除新分片的system.sessions集合。

config.transactions

The transactions collection stores records used to support retryable writes and transactions for replica sets and sharded clusters.

Warning警告

Do not manually modify or drop the transactions collection.不要手动修改或删除transactions集合。