This guide describes how DynamoDB billing works for global tables, identifying the components that contribute to the cost of global tables, including a practical example.
Amazon DynamoDB global tables is a fully managed,
serverless, multi-Region, and multi-active database. Global tables are designed for
99.999% availability
How it works
The billing model for global tables differs from single-Region DynamoDB tables. Write operations for single-Region DynamoDB tables are billed using the following units:
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Write Request Units (WRUs) for on-demand capacity mode, where one WRU is charged for each write up to 1KB
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Write Capacity Units (WCUs) for provisioned capacity mode, where one WCU provides one write per second for up to 1 KB
When you create a global table by adding a replica table to an existing single-Region table, that single-Region table becomes a replica table, which means the units used to bill for writes to the table also change. Write operations to replica tables are billed using the following units:
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Replicated Write Request Units (rWRUs) for on-demand capacity mode, where one rWRU per replica table is charged for each write up to 1KB
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Replicated Write Capacity Units (rWCUs) for provisioned capacity mode, where one WCU per replica table provides one write per second for up to 1 KB
Updates to Global Secondary Indexes (GSIs) are billed using the same units as single-Region DynamoDB tables, even if the base table for the GSI is a replica table. Update operations for GSIs are billed using the following units:
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Write Request Units (WRUs) for on-demand capacity mode, where one WRU is charged for each write up to 1KB
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Write Capacity Units (WCUs) for provisioned capacity mode, where one WCU provides one write per second for up to 1 KB
Replicated write units (rWCUs and rWRUs) are priced the same as single-Region write units (WCUs and WRUs). Cross-Region data transfer fees apply for global tables as data is replicated across Regions. Replicated write (rWCU or rWRU) charges are incurred in every Region containing a replica table for the global table.
Read operations from single-Region tables and from replica tables use the following units::
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Read Request Units (RRUs) for on-demand capacity mode, where one RRU is charged for each strongly consistent read up to 4KB
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Read Capacity Units (RCUs) for provisioned tables, where one RCU provides one strongly consistent read per second for up to 4KB
DynamoDB global tables billing
example
Let's walk through a multi-day example scenario to see how global table write request billing works in practice (note that this example only considers write requests, and does not include the table restore and cross-Region data transfer charges that would be incurred in the example):
Day 1 - Single-Region table: You have a single-Region on-demand DynamoDB table named Table_A in the us-west-2 Region. You write 100 1KB items to Table_A. For these single-Region write operations, you are charged 1 write request unit (WRU) per 1KB written. Your day 1 charges are:
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100 WRUs in the us-west-2 Region for single-Region writes
The total request units charged on day 1: 100 WRUs.
Day 2 - Creating a global table: You create a global table by adding a replica to Table_A in the us-east-2 Region. Table_A is now a global table with two replica tables; one in the us-west-2 Region, and one in the us-east-2 Region. You write 150 1KB items to the replica table in the us-west-2 Region. Your day 2 charges are:
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150 rWRUs in the us-west-2 Region for replicated writes
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150 rWRUs in the us-east-2 Region for replicated writes
The total request units charged on day 2: 300 rWRUs.
Day 3 - Adding a Global Secondary Index: You add a global secondary index (GSI) to the replica table in the us-east-2 Region that projects all attributes from the base (replica) table. The global table automatically creates the GSI on the replica table in the us-west-2 Region for you. You write 200 new 1KB records to the replica table in the us-west-2 Region. Your day 3 charges are:
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• 200 rWRUs in the us-west-2 Region for replicated writes
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• 200 WRUs in the us-west-2 Region for GSI updates
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• 200 rWRUs in the us-east-2 Region for replicated writes
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• 200 WRUs in the us-east-2 Region for GSI updates
The total write request units charged on day 3: 400 WRUs and 400 rWRUs.
The total write unit charges for all three days are 500WRUs (100 WRU on day 1 + 400 WRUs on day 3) and 700 rWRUs (300 rWRUs on Day2 + 400 rWRUs on Day 3).
In summary, replica table write operations are billed in replicated write units in all Regions that contain a replica table. If you have global secondary indexes, you are charged write units for updates to GSIs in all regions that contain a GSI (which in a global table is all Regions that contain a replica table).
