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Amazon DynamoDB
Developer Guide (API Version 2012-08-10)

Limits in DynamoDB

This section describes current limits within Amazon DynamoDB (or no limit, in some cases). Each limit listed below applies on a per-region basis unless otherwise specified.

Capacity Units and Provisioned Throughput

Capacity Unit Sizes

One read capacity unit = one strongly consistent read per second, or two eventually consistent reads per second, for items up to 4 KB in size.

One write capacity unit = one write per second, for items up to 1 KB in size.

Provisioned Throughput Minimums and Maximums

For any table or global secondary index, the minimum settings for provisioned throughput are 1 read capacity unit and 1 write capacity unit.

An AWS account places some initial maximum limits on the throughput you can provision:

  • US East (N. Virginia) Region:

    • Per table – 40,000 read capacity units and 40,000 write capacity units

    • Per account – 80,000 read capacity units and 80,000 write capacity units

  • All Other Regions:

    • Per table – 10,000 read capacity units and 10,000 write capacity units

    • Per account – 20,000 read capacity units and 20,000 write capacity units

The provisioned throughput limit includes the sum of the capacity of the table together with the capacity of all of its global secondary indexes.

You can request an increase on any of these limits. For more information, see http://aws.amazon.com/support.

In the AWS Management Console, you can see what your current provisioned capacity is in a given region and make sure you are not too close to the limits. If you increased your default limits, you can use the DescribeLimits operation to see the current limit values.

Increasing Provisioned Throughput

You can increase ReadCapacityUnits or WriteCapacityUnits as often as necessary, using the AWS Management Console or the UpdateTable operation. In a single call, you can increase the provisioned throughput for a table, for any global secondary indexes on that table, or for any combination of these. The new settings do not take effect until the UpdateTable operation is complete.

You cannot exceed your per-account limits when you add provisioned capacity, and DynamoDB will not permit you to increase provisioned capacity extremely rapidly. Aside from these restrictions, you can increase the provisioned capacity for your tables as high as you need. For more information about per-account limits, see the preceding section Provisioned Throughput Minimums and Maximums.

Decreasing Provisioned Throughput

You can decrease the ReadCapacityUnits or WriteCapacityUnits settings for a table, but no more than four times per table in a single UTC calendar day. In a single operation, you can decrease the provisioned throughput for a table, for any global secondary indexes on that table, or for any combination of these.

For every table and global secondary index in an UpdateTable operation, you can decrease ReadCapacityUnits or WriteCapacityUnits (or both). The new settings do not take effect until the UpdateTable operation is complete.

Tables

Table Size

There is no practical limit on a table's size. Tables are unconstrained in terms of the number of items or the number of bytes.

Tables Per Account

For any AWS account, there is an initial limit of 256 tables per region.

You can request an increase on this limit. For more information, go to http://aws.amazon.com/support.

Secondary Indexes

Secondary Indexes Per Table

You can define a maximum of 5 local secondary indexes and 5 global secondary indexes per table.

Projected Secondary Index Attributes Per Table

You can project a total of up to 20 attributes into all of a table's local and global secondary indexes. This only applies to user-specified projected attributes.

In a CreateTable operation, if you specify a ProjectionType of INCLUDE, the total count of attributes specified in NonKeyAttributes, summed across all of the secondary indexes, must not exceed 20. If you project the same attribute name into two different indexes, this counts as two distinct attributes when determining the total.

This limit does not apply for secondary indexes with a ProjectionType of KEYS_ONLY or ALL.

Partition Keys and Sort Keys

Partition Key Length

The minimum length of a partition key value is 1 byte. The maximum length is 2048 bytes.

Partition Key Values

There is no practical limit on the number of distinct partition key values, for tables or for secondary indexes.

Sort Key Length

The minimum length of a sort key value is 1 byte. The maximum length is 1024 bytes.

Sort Key Values

In general, there is no practical limit on the number of distinct sort key values per partition key value.

The exception is for tables with local secondary indexes. With a local secondary index, there is a limit on item collection sizes: For every distinct partition key value, the total sizes of all table and index items cannot exceed 10 GB. This might constrain the number of sort keys per partition key value. For more information, see Item Collection Size Limit.

Naming Rules

Table Names and Secondary Index Names

Names for tables and secondary indexes must be at least 3 characters long, but no greater than 255 characters long. Allowed characters are:

  • A-Z

  • a-z

  • 0-9

  • _ (underscore)

  • - (hyphen)

  • . (dot)

Attribute Names

In general, an attribute name must be at least 1 character long, but no greater than 64 KB long.

The exceptions are listed below. These attribute names must be no greater than 255 characters long:

  • Secondary index partition key names.

  • Secondary index sort key names.

  • The names of any user-specified projected attributes (applicable only to local secondary indexes). In a CreateTable operation, if you specify a ProjectionType of INCLUDE, then the names of the attributes in the NonKeyAttributes parameter are length-restricted. The KEYS_ONLY and ALL projection types are not affected.

These attribute names must be encoded using UTF-8, and the total size of each name (after encoding) cannot exceed 255 bytes.

Data Types

String

The length of a String is constrained by the maximum item size of 400 KB.

Strings are Unicode with UTF-8 binary encoding. Because UTF-8 is a variable width encoding, DynamoDB determines the length of a String using its UTF-8 bytes.

Number

A Number can have up to 38 digits of precision, and can be positive, negative, or zero.

  • Positive range: 1E-130 to 9.9999999999999999999999999999999999999E+125

  • Negative range: -9.9999999999999999999999999999999999999E+125 to -1E-130

DynamoDB uses JSON strings to represent Number data in requests and replies. For more information, see DynamoDB Low-Level API.

If number precision is important, you should pass numbers to DynamoDB using strings that you convert from a number type.

Binary

The length of a Binary is constrained by the maximum item size of 400 KB.

Applications that work with Binary attributes must encode the data in Base64 format before sending it to DynamoDB. Upon receipt of the data, DynamoDB decodes it into an unsigned byte array and uses that as the length of the attribute.

Items

Item Size

The maximum item size in DynamoDB is 400 KB, which includes both attribute name binary length (UTF-8 length) and attribute value lengths (again binary length). The attribute name counts towards the size limit.

For example, consider an item with two attributes: one attribute named "shirt-color" with value "R" and another attribute named "shirt-size" with value "M". The total size of that item is 23 bytes.

Item Size for Tables With Local Secondary Indexes

For each local secondary index on a table, there is a 400 KB limit on the total of the following:

  • The size of an item's data in the table.

  • The size of the local secondary index entry corresponding to that item, including its key values and projected attributes.

Attributes

Attribute Name-Value Pairs Per Item

The cumulative size of attributes per item must fit within the maximum DynamoDB item size (400 KB).

Number of Values in List, Map, or Set

There is no limit on the number of values in a List, a Map, or a Set, as long as the item containing the values fits within the 400 KB item size limit.

Attribute Values

An attribute value cannot be an empty String or empty Set (String Set, Number Set, or Binary Set). However, empty Lists and Maps are allowed.

Nested Attribute Depth

DynamoDB supports nested attributes up to 32 levels deep.

Expression Parameters

Expression parameters include ProjectionExpression, ConditionExpression, UpdateExpression, and FilterExpression.

Lengths

The maximum length of any expression string is 4 KB. For example, the size of the ConditionExpression a=b is three bytes.

The maximum length of any single expression attribute name or expression attribute value is 255 bytes. For example, #name is five bytes; :val is four bytes.

The maximum length of all substitution variables in an expression is 2 MB. This is the sum of the lengths of all ExpressionAttributeNames and ExpressionAttributeValues.

Operators and Operands

The maximum number of operators or functions allowed in an UpdateExpression is 300. For example, the UpdateExpression SET a = :val1 + :val2 + :val3 contains two "+" operators.

The maximum number of operands for the IN comparator is 100

Reserved Words

DynamoDB does not prevent you from using names that conflict with reserved words. (For a complete list, see Reserved Words in DynamoDB.)

However, if you use a reserved word in an expression parameter, you must also specify ExpressionAttributeNames. For more information, see Using Placeholders for Attribute Names and Values.

DynamoDB Streams

Simultaneous Readers of a Shard in DynamoDB Streams

Do not allow more than two processes to read from the same DynamoDB Streams shard at the same time. Exceeding this limit can result in request throttling.

API-Specific Limits

CreateTable/UpdateTable/DeleteTable

In general, you can have up to 10 CreateTable, UpdateTable, and DeleteTable requests running simultaneously (in any combination). In other words, the total number of tables in the CREATING, UPDATING or DELETING state cannot exceed 10.

The only exception is when you are creating a table with one or more secondary indexes. You can have up to 5 such requests running at a time; however, if the table or index specifications are complex, DynamoDB might temporarily reduce the number of concurrent requests below 5.

BatchGetItem

A single BatchGetItem operation can retrieve a maximum of 100 items. The total size of all the items retrieved cannot exceed 16 MB.

BatchWriteItem

A single BatchWriteItem operation can contain up to 25 PutItem or DeleteItem requests. The total size of all the items written cannot exceed 16 MB.

DescribeLimits

DescribeLimits should only be called periodically. You can expect throttling errors if you call it more than once in a minute.

Query

The result set from a Query is limited to 1 MB per call. You can use the LastEvaluatedKey from the query response to retrieve more results.

Scan

The result set from a Scan is limited to 1 MB per call. You can use the LastEvaluatedKey from the scan response to retrieve more results.