Provisioned capacity mode
When you create a new provisioned table in DynamoDB, you must specify its provisioned throughput capacity. This is the amount of read and write throughput that the table can support. DynamoDB uses this information to ensure there are sufficient system resources to meet your throughput requirements.
You can optionally allow DynamoDB auto scaling to manage your table's throughput capacity. To use auto scaling, you must provide the initial settings for read and write capacity when you create the table. DynamoDB auto scaling uses these initial settings as a starting point and then adjusts them dynamically in response to your application's requirements. For more information, see Managing throughput capacity automatically with DynamoDB auto scaling.
As your application's data and access requirements change, you might need to adjust your table's throughput settings. If you're using DynamoDB auto scaling, the throughput settings are automatically adjusted in response to actual workloads. You can also use the UpdateTable operation to manually adjust your table's throughput capacity. You might decide to do this if you need to bulk-load data from an existing data store into your new DynamoDB table. You could create the table with a large write throughput setting and then reduce this setting after the bulk data load is complete.
You can switch tables from on-demand mode to provisioned capacity mode at any time. When you do multiple switches between capacity modes, the following conditions apply:
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You can switch a newly created table in on-demand mode to provisioned capacity mode at any time. However, you can only switch it back to on-demand mode 24 hours after the table’s creation timestamp.
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You can switch an existing table in on-demand mode to provisioned capacity mode at any time. However, you can only switch it back to on-demand mode 24 hours after the last timestamp indicating a switch to on-demand.
For more information about switching between read and write capacity modes, see Considerations when switching capacity modes.
Topics
Read capacity units and write capacity units
For provisioned mode tables, you specify throughput requirements in terms of capacity units. These units represent the amount of data your application needs to read or write per second. You can modify these settings later, if needed, or enable DynamoDB auto scaling to modify them automatically.
For an item up to 4 KB, one read capacity unit represents one strongly consistent read operation per second, or two eventually consistent read operations per second. For more information about DynamoDB read consistency models, see Read consistency.
A write capacity unit represents one write per second for an item up to 1 KB. For more information about the different read and write operations, see Read and write operations.
Choosing initial throughput settings
Every application has different requirements for reading from and writing to a database. When you're determining the initial throughput settings for a DynamoDB table, consider the following:
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Expected read and write request rates — You should estimate the number of reads and writes you need to perform per second.
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Item sizes — Some items are small enough that they can be read or written using a single capacity unit. Larger items require multiple capacity units. By estimating the average size of the items that will be in your table, you can specify accurate settings for your table's provisioned throughput.
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Read consistency requirements — Read capacity units are based on strongly consistent read operations, which consume twice as many database resources as eventually consistent reads. You should determine whether your application requires strongly consistent reads, or whether it can relax this requirement and perform eventually consistent reads instead. Read operations in DynamoDB are eventually consistent, by default. You can request strongly consistent reads for these operations, if necessary.
For example, say that you want to read 80 items per second from a table. The size of these items is 3 KB, and you want strongly consistent reads. In this case, each read requires one provisioned read capacity unit. To determine this number, divide the item size of the operation by 4 KB. Then, round up to the nearest whole number, as shown in the following example:
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3 KB / 4 KB = 0.75 or 1 read capacity unit
Therefore, to read 80 items per second from a table, set the table's provisioned read throughput to 80 read capacity units as shown in the following example:
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1 read capacity unit per item × 80 reads per second = 80 read capacity units
Now suppose that you want to write 100 items per second to your table and that the size of each item is 512 bytes. In this case, each write requires one provisioned write capacity unit. To determine this number, divide the item size of the operation by 1 KB. Then, round up to the nearest whole number, as shown in the following example:
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512 bytes / 1 KB = 0.5 or 1 write capacity unit
To write 100 items per second to your table, set the table's provisioned write throughput to 100 write capacity units:
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1 write capacity unit per item × 100 writes per second = 100 write capacity units
DynamoDB auto scaling
DynamoDB auto scaling actively manages provisioned throughput capacity for tables and global secondary indexes. With auto scaling, you define a range (upper and lower limits) for read and write capacity units. You also define a target utilization percentage within that range. DynamoDB auto scaling seeks to maintain your target utilization, even as your application workload increases or decreases.
With DynamoDB auto scaling, a table or a global secondary index can increase its provisioned read and write capacity to handle sudden increases in traffic, without request throttling. When the workload decreases, DynamoDB auto scaling can decrease the throughput so that you don't pay for unused provisioned capacity.
Note
If you use the AWS Management Console to create a table or a global secondary index, DynamoDB auto scaling is enabled by default.
You can manage auto scaling settings at any time by using the console, the AWS CLI, or one of the AWS SDKs. For more information, see Managing throughput capacity automatically with DynamoDB auto scaling.
Utilization rate
Utilization rate can help you determine if you’re over provisioning capacity, in which case should reduce your table capacity to save costs. Conversely, it can also help you determine if you’re under provisioning capacity. In this case, you should increase table capacity to prevent potential throttling of requests during unexpected high traffic instances. For more information, see Amazon DynamoDB auto scaling: Performance and cost optimization at any scale
If you’re using DynamoDB auto scaling, you’ll also need to set a target utilization percentage. Auto scaling will use this percentage as a target to adjust capacity upward or downward. We recommend setting target utilization to 70%. For more information, see Managing throughput capacity automatically with DynamoDB auto scaling.
