How reservation discounts apply to Azure SQL Data Warehouse
After you buy Azure SQL Data Warehouse reserved capacity, the reservation discount is automatically applied to data warehouses that exist in that region. The reservation discount applies to the usage emitted by the SQL Data Warehouse cDWU meter. Storage and networking are charged at pay-as-you-go rates.
Reservation discount application
The SQL Data Warehouse reserved capacity discount is applied to running warehouses on an hourly basis. If you don't have a warehouse deployed for an hour, then the reserved capacity is wasted for that hour. It doesn't carry over.
After purchase, the reservation that you buy is matched to SQL Data Warehouse usage emitted by running warehouses at any point in time. If you shut down some warehouses, then reservation discounts automatically apply to any other matching warehouses.
For warehouses that don't run for a full hour, the reservation is automatically applied to other matching instances in that hour.
The following examples show how the SQL Data Warehouse reserved capacity discount applies, depending on the deployments.
Example 1: You purchase 5 units of 100 cDWU reserved capacity. You run a DW1500c SQL Data Warehouse instance for an hour. In this case, usage is emitted for 15 units of 100 cDWU usage. The reservation discount applies to the 5 units that you used. You are charged using pay-as-you-go rates for the remaining 10 units of 100 cDWU usage that you used. In other words, partial coverage is possible for multiple reservations.
Example 2: You purchase 5 units of 100 cDWU reserved capacity. You run two DW100c SQL Data Warehouse instances for an hour. In this case, two usage events are emitted for 1 unit of 100 cDWU usage. Both usage events get reserved capacity discounts. The remaining 3 units of 100 cDWU reserved capacity are wasted and don't carry over for future use. In other words, a single reservation can get matched to multiple SQL Data Warehouse instances.
Example 3: You purchase 1 unit of 100 cDWU reserved capacity. You run two DW100c SQL Data Warehouse instances. Each runs for 30 minutes. In this case, both usage events get reserved capacity discounts. No usage is charged using pay-as-you-go rates.
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To learn more about Azure Reservations, see the following articles: