Hướng dẫn mongodb atlas limits

Atlas sets the limits for concurrent incoming connections based on the cluster tier and class. Atlas connection limits apply per node. For sharded clusters, Atlas connection limits apply per mongos router. The number of mongos routers is equal to the number of replica set nodes across all shards.

Your read preference also contributes to the total number of connections Atlas can allocate for a given query.

Example

Your M2 cluster has three nodes with a 500 connection limit per node. Atlas reserves 10 connections per node. If you set your read preference to secondary, Atlas can read from the two secondary nodes for a combined 980 connection limit.

Note

Atlas reserves a small number of connections to each Atlas cluster for supporting Atlas services. Contact Atlas support for more information on Atlas reserved connections.

While there is no hard limit on the number of collections in a single cluster, the performance of a cluster might degrade if it serves a large number of collections and indexes. Larger collections have a greater impact on performance.

The recommended maximum combined number of collections and indexes by Atlas cluster tier are as follows:

Atlas also limits how long particular labels of components can be.

To learn more about unsupported commands, see the unsupported commands for free or shared clusers, paid clusters, and serverless instances

Serverless instances have different limitations. To learn more, see Serverless Instance Limitations.

The maximum BSON document size is 16 megabytes.

The maximum document size helps ensure that a single document cannot use excessive amount of RAM or, during transmission, excessive amount of bandwidth. To store documents larger than the maximum size, MongoDB provides the GridFS API. See mongofiles and the documentation for your driver for more information about GridFS.

MongoDB supports no more than 100 levels of nesting for BSON documents. Each object or array adds a level.

Do not rely on case to distinguish between databases. For example, you cannot use two databases with names like, salesData and SalesData.

After you create a database in MongoDB, you must use consistent capitalization when you refer to it. For example, if you create the salesData database, do not refer to it using alternate capitalization such as salesdata or SalesData.

For MongoDB deployments running on Windows, database names cannot contain any of the following characters:

Also database names cannot contain the null character.

For MongoDB deployments running on Unix and Linux systems, database names cannot contain any of the following characters:

Also database names cannot contain the null character.

Database names cannot be empty and must have fewer than 64 characters.

Collection names should begin with an underscore or a letter character, and cannot:

• contain the $.

• be an empty string (e.g. "").

• contain the null character.

• begin with the system. prefix. (Reserved for internal use.)

If your collection name includes special characters, such as the underscore character, or begins with numbers, then to access the collection use the db.getCollection() method in mongosh or a similar method for your driver.

Namespace Length:

• For featureCompatibilityVersion set to "4.4" or greater, MongoDB raises the limit for unsharded collections and views to 255 bytes, and to 235 bytes for sharded collections. For a collection or a view, the namespace includes the database name, the dot (.) separator, and the collection/view name (e.g. <database>.<collection>),

• For featureCompatibilityVersion set to "4.2" or earlier, the maximum length of unsharded collections and views namespace remains 120 bytes and 100 bytes for sharded collection.

• Field names cannot contain the null character.

• The server permits storage of field names that contain dots (.) and dollar signs ($).

• MongodB 5.0 adds improved support for the use of ($) and (.) in field names. There are some restrictions. See Field Name Considerations for more details.

The field name _id is reserved for use as a primary key; its value must be unique in the collection, is immutable, and may be of any type other than an array. If the _id contains subfields, the subfield names cannot begin with a ($) symbol.

Warning

Use caution, the issues discussed in this section could lead to data loss or corruption.

• For featureCompatibilityVersion set to "4.4" or greater, MongoDB raises the limit for unsharded collections and views to 255 bytes, and to 235 bytes for sharded collections. For a collection or a view, the namespace includes the database name, the dot (.) separator, and the collection/view name (e.g. <database>.<collection>),

• For featureCompatibilityVersion set to "4.2" or earlier, the maximum length of unsharded collections and views namespace remains 120 bytes and 100 bytes for sharded collection.

Tip

See also:

Note

Changed in version 4.2

For MongoDB 2.6 through MongoDB versions with fCV set to "4.0" or earlier, the total size of an index entry, which can include structural overhead depending on the BSON type, must be less than 1024 bytes.

When the Index Key Limit applies:

• MongoDB will not create an index on a collection if the index entry for an existing document exceeds the index key limit.

• Reindexing operations will error if the index entry for an indexed field exceeds the index key limit. Reindexing operations occur as part of the compact command as well as the db.collection.reIndex() method.

  Because these operations drop all the indexes from a collection and then recreate them sequentially, the error from the index key limit prevents these operations from rebuilding any remaining indexes for the collection.

• MongoDB will not insert into an indexed collection any document with an indexed field whose corresponding index entry would exceed the index key limit, and instead, will return an error. Previous versions of MongoDB would insert but not index such documents.

• Updates to the indexed field will error if the updated value causes the index entry to exceed the index key limit.

  If an existing document contains an indexed field whose index entry exceeds the limit, any update that results in the relocation of that document on disk will error.

• mongorestore and mongoimport will not insert documents that contain an indexed field whose corresponding index entry would exceed the index key limit.

• In MongoDB 2.6, secondary members of replica sets will continue to replicate documents with an indexed field whose corresponding index entry exceeds the index key limit on initial sync but will print warnings in the logs.

  Secondary members also allow index build and rebuild operations on a collection that contains an indexed field whose corresponding index entry exceeds the index key limit but with warnings in the logs.

  With mixed version replica sets where the secondaries are version 2.6 and the primary is version 2.4, secondaries will replicate documents inserted or updated on the 2.4 primary, but will print error messages in the log if the documents contain an indexed field whose corresponding index entry exceeds the index key limit.

• For existing sharded collections, chunk migration will fail if the chunk has a document that contains an indexed field whose index entry exceeds the index key limit.

A single collection can have no more than 64 indexes.

Note

Changed in version 4.2

In previous versions of MongoDB or MongoDB versions with fCV set to "4.0" or earlier, fully qualified index names, which include the namespace and the dot separators (i.e. <database name>.<collection name>.$<index name>), cannot be longer than 127 bytes.

By default, <index name> is the concatenation of the field names and index type. You can explicitly specify the <index name> to the createIndex() method to ensure that the fully qualified index name does not exceed the limit.

There can be no more than 32 fields in a compound index.

You cannot combine the $text query, which requires a special text index, with a query operator that requires a different type of special index. For example you cannot combine $text query with the $near operator.

Fields with 2dsphere indexes must hold geometry data in the form of coordinate pairs or GeoJSON data. If you attempt to insert a document with non-geometry data in a 2dsphere indexed field, or build a 2dsphere index on a collection where the indexed field has non-geometry data, the operation will fail.

Tip

See also:

To generate keys for a 2dsphere index, mongod maps GeoJSON shapes to an internal representation. The resulting internal representation may be a large array of values.

When mongod generates index keys on a field that holds an array, mongod generates an index key for each array element. For compound indexes, mongod calculates the cartesian product of the sets of keys that are generated for each field. If both sets are large, then calculating the cartesian product could cause the operation to exceed memory limits.

indexMaxNumGeneratedKeysPerDocument limits the maximum number of keys generated for a single document to prevent out of memory errors. The default is 100000 index keys per document. It is possible to raise the limit, but if an operation requires more keys than the indexMaxNumGeneratedKeysPerDocument parameter specifies, the operation will fail.

If the value of a field returned from a query that is covered by an index is NaN, the type of that NaN value is always double.

Multikey indexes cannot cover queries over array field(s).

Geospatial indexes cannot cover a query.

createIndexes supports building one or more indexes on a collection. createIndexes uses a combination of memory and temporary files on disk to complete index builds. The default limit on memory usage for createIndexes is 200 megabytes (for versions 4.2.3 and later) and 500 (for versions 4.2.2 and earlier), shared between all indexes built using a single createIndexes command. Once the memory limit is reached, createIndexes uses temporary disk files in a subdirectory named _tmp within the --dbpath directory to complete the build.

You can override the memory limit by setting the maxIndexBuildMemoryUsageMegabytes server parameter. Setting a higher memory limit may result in faster completion of index builds. However, setting this limit too high relative to the unused RAM on your system can result in memory exhaustion and server shutdown.

Changed in version 4.2.

• For feature compatibility version (fcv) "4.2", the index build memory limit applies to all index builds.

• For feature compatibility version (fcv) "4.0", the index build memory limit only applies to foreground index builds.

Index builds may be initiated either by a user command such as Create Index or by an administrative process such as an initial sync. Both are subject to the limit set by maxIndexBuildMemoryUsageMegabytes

An initial sync operation populates only one collection at a time and has no risk of exceeding the memory limit. However, it is possible for a user to start index builds on multiple collections in multiple databases simultaneously and potentially consume an amount of memory greater than the limit set in maxIndexBuildMemoryUsageMegabytes

Tip

To minimize the impact of building an index on replica sets and sharded clusters with replica set shards, use a rolling index build procedure as described on Rolling Index Builds on Replica Sets.

The following index types only support simple binary comparison and do not support collation:

• text indexes,

• 2d indexes, and

• geoHaystack indexes.

Tip

To create a text, a 2d, or a geoHaystack index on a collection that has a non-simple collation, you must explicitly specify {collation: {locale: "simple"} } when creating the index.

• You cannot hide the _id index.

• You cannot use hint() on a hidden index.

You can sort on a maximum of 32 keys.

If you specify the maximum number of documents in a capped collection with create's max parameter, the value must be less than 2 31 documents.

If you do not specify a maximum number of documents when creating a capped collection, there is no limit on the number of documents.

Replica sets can have up to 50 members.

Replica sets can have up to 7 voting members. For replica sets with more than 7 total members, see Non-Voting Members.

If you do not explicitly specify an oplog size (i.e. with oplogSizeMB or --oplogSize) MongoDB will create an oplog that is no larger than 50 gigabytes. [1]

Sharded clusters have the restrictions and thresholds described here.

maxSplits = 16777216 (bytes) / <average size of shard key values in bytes>
maxCollectionSize (MB) = maxSplits * (chunkSize / 2)

If MongoDB cannot use an index or indexes to obtain the sort order, MongoDB must perform a blocking sort operation on the data. The name refers to the requirement that the SORT stage reads all input documents before returning any output documents, blocking the flow of data for that specific query.

If MongoDB requires using more than 100 megabytes of system memory for the blocking sort operation, MongoDB returns an error unless the query specifies cursor.allowDiskUse() (New in MongoDB 4.4). allowDiskUse() allows MongoDB to use temporary files on disk to store data exceeding the 100 megabyte system memory limit while processing a blocking sort operation.

Changed in version 4.4: For MongoDB 4.2 and prior, blocking sort operations could not exceed 32 megabytes of system memory.

For more information on sorts and index use, see Sort and Index Use.

Starting in MongoDB 6.0, the allowDiskUseByDefault parameter controls whether pipeline stages that require more than 100 megabytes of memory to execute write temporary files to disk by default.

• If allowDiskUseByDefault is set to true, pipeline stages that require more than 100 megabytes of memory to execute write temporary files to disk by default. You can disable writing temporary files to disk for specific find or aggregate commands using the { allowDiskUse: false } option.

• If allowDiskUseByDefault is set to false, pipeline stages that require more than 100 megabytes of memory to execute raise an error by default. You can enable writing temporary files to disk for specific find or aggregate using the { allowDiskUse: true } option.

The $search aggregation stage is not restricted to 100 megabytes of RAM because it runs in a separate process.

Examples of stages that can write temporary files to disk when allowDiskUse is true are:

• $bucket

• $bucketAuto

• $group

• $setWindowFields

• $sort when the sort operation is not supported by an index

• $sortByCount

Note

Pipeline stages operate on streams of documents with each pipeline stage taking in documents, processing them, and then outputing the resulting documents.

Some stages can't output any documents until they have processed all incoming documents. These pipeline stages must keep their stage output in RAM until all incoming documents are processed. As a result, these pipeline stages may require more space than the 100 MB limit.

If the results of one of your $sort pipeline stages exceed the limit, consider adding a $limit stage.

Starting in MongoDB 4.2, the profiler log messages and diagnostic log messages includes a usedDisk indicator if any aggregation stage wrote data to temporary files due to memory restrictions.

• Starting in MongoDB 4.2, the $out stage cannot be used in conjunction with read concern "linearizable". That is, if you specify "linearizable" read concern for db.collection.aggregate(), you cannot include the $out stage in the pipeline.

• The $merge stage cannot be used in conjunction with read concern "linearizable". That is, if you specify "linearizable" read concern for db.collection.aggregate(), you cannot include the $merge stage in the pipeline.

Tip

For spherical queries, use the 2dsphere index result.

The use of 2d index for spherical queries may lead to incorrect results, such as the use of the 2d index for spherical queries that wrap around the poles.

• Valid longitude values are between -180 and 180, both inclusive.

• Valid latitude values are between -90 and 90, both inclusive.

For $geoIntersects or $geoWithin, if you specify a single-ringed polygon that has an area greater than a single hemisphere, include the custom MongoDB coordinate reference system in the $geometry expression; otherwise, $geoIntersects or $geoWithin queries for the complementary geometry. For all other GeoJSON polygons with areas greater than a hemisphere, $geoIntersects or $geoWithin queries for the complementary geometry.

For multi-document transactions:

• You can specify read/write (CRUD) operations on existing collections. For a list of CRUD operations, see CRUD Operations.

• Starting in MongoDB 4.4, you can create collections and indexes in transactions. For details, see Create Collections and Indexes In a Transaction

• The collections used in a transaction can be in different databases.

  Note

  You cannot create new collections in cross-shard write transactions. For example, if you write to an existing collection in one shard and implicitly create a collection in a different shard, MongoDB cannot perform both operations in the same transaction.

• You cannot write to capped collections. (Starting in MongoDB 4.2)

• You cannot use read concern "snapshot" when reading from a capped collection. (Starting in MongoDB 5.0)

• You cannot read/write to collections in the config, admin, or local databases.

• You cannot write to system.* collections.

• You cannot return the supported operation's query plan (i.e. explain).

• For cursors created outside of a transaction, you cannot call getMore inside the transaction.

• For cursors created in a transaction, you cannot call getMore outside the transaction.

• Starting in MongoDB 4.2, you cannot specify killCursors as the first operation in a transaction.

Changed in version 4.4.

The following operations are not allowed in transactions:

• Operations that affect the database catalog, such as creating or dropping a collection or an index when using MongoDB 4.2 or lower. Starting in MongoDB 4.4, you can create collections and indexes in transactions unless the transaction is a cross-shard write transaction. For details, see Create Collections and Indexes In a Transaction.

• Creating new collections in cross-shard write transactions. For example, if you write to an existing collection in one shard and implicitly create a collection in a different shard, MongoDB cannot perform both operations in the same transaction.

• Explicit creation of collections, e.g. db.createCollection() method, and indexes, e.g. db.collection.createIndexes() and db.collection.createIndex() methods, when using a read concern level other than "local"

• The listCollections and listIndexes commands and their helper methods.

• Other non-CRUD and non-informational operations, such as createUser, getParameter, count, etc. and their helpers.

Transactions have a lifetime limit as specified by transactionLifetimeLimitSeconds. The default is 60 seconds.

100,000 writes are allowed in a single batch operation, defined by a single request to the server.

Changed in version 3.6: The limit raises from 1,000 to 100,000 writes. This limit also applies to legacy OP_INSERT messages.

The Bulk() operations in mongosh and comparable methods in the drivers do not have this limit.

A view definition pipeline cannot include the $out or the $merge stage. This restriction also applies to embedded pipelines, such as pipelines used in $lookup or $facet stages.

Views have the following operation restrictions:

• Views are read-only.

• You cannot rename views.

• find() operations on views do not support the following projection operators:

  • $

  • $elemMatch

  • $slice

  • $meta

• Views do not support text search.

• Views do not support map-reduce operations.

• Views do not support geoNear operations (i.e. $geoNear pipeline stage).

New in version 4.4:

db.inventory.find( {}, { "$instock.warehouse": 0, "$item": 0, "detail.$price": 1 } ) // Invalid starting in 4.4

db.inventory.find( { }, { "instock.$.qty": 1 } ) // Invalid starting in 4.4

db.inventory.find( { }, { "": 0 } ) // Invalid starting in 4.4

{ ..., size: { h: 10, w: 15.25, uom: "cm" }, ... }

db.inventory.find( {}, { size: 1, "size.uom": 1 } )  // Invalid starting in 4.4

• If the projection of the embedded document comes after any and all projections of its fields, MongoDB projects the embedded document. For example, the projection document { "size.uom": 1, size: 1 } produces the same result as the projection document { size: 1 }.

• If the projection of the embedded document comes before the projection any of its fields, MongoDB projects the specified field or fields. For example, the projection document { "size.uom": 1, size: 1, "size.h": 1 } produces the same result as the projection document { "size.uom": 1, "size.h": 1 }.

{ ..., instock: [ { warehouse: "A", qty: 35 }, { warehouse: "B", qty: 15 }, { warehouse: "C", qty: 35 } ], ... }

db.inventory.find( {}, { "instock": { $slice: 1 }, "instock.warehouse": 0 } ) // Invalid starting in 4.4

db.inventory.find( { "instock.qty": { $gt: 25 } }, { "instock.$": { $slice: 1 } } ) // Invalid starting in 4.4

To use Client Sessions and Causal Consistency Guarantees with $external authentication users (Kerberos, LDAP, or x.509 users), usernames cannot be greater than 10k bytes.

Sessions that receive no read or write operations for 30 minutes or that are not refreshed using refreshSessions within this threshold are marked as expired and can be closed by the MongoDB server at any time. Closing a session kills any in-progress operations and open cursors associated with the session. This includes cursors configured with noCursorTimeout() or a maxTimeMS() greater than 30 minutes.

Consider an application that issues a db.collection.find(). The server returns a cursor along with a batch of documents defined by the cursor.batchSize() of the find(). The session refreshes each time the application requests a new batch of documents from the server. However, if the application takes longer than 30 minutes to process the current batch of documents, the session is marked as expired and closed. When the application requests the next batch of documents, the server returns an error as the cursor was killed when the session was closed.

For operations that return a cursor, if the cursor may be idle for longer than 30 minutes, issue the operation within an explicit session using Mongo.startSession() and periodically refresh the session using the refreshSessions command. For example:

var session = db.getMongo().startSession()
var sessionId = session.getSessionId().id
var cursor = session.getDatabase("examples").getCollection("data").find().noCursorTimeout()
var refreshTimestamp = new Date() // take note of time at operation start
while (cursor.hasNext()) {
  // Check if more than 5 minutes have passed since the last refresh
  if ( (new Date()-refreshTimestamp)/1000 > 300 ) {
    print("refreshing session")
    db.adminCommand({"refreshSessions" : [sessionId]})
    refreshTimestamp = new Date()
  }
  // process cursor normally
}

In the example operation, the db.collection.find() method is associated with an explicit session. The cursor is configured with noCursorTimeout() to prevent the server from closing the cursor if idle. The while loop includes a block that uses refreshSessions to refresh the session every 5 minutes. Since the session will never exceed the 30 minute idle timeout, the cursor can remain open indefinitely.

For MongoDB drivers, defer to the driver documentation for instructions and syntax for creating sessions.