Read/write throughput

Last Updated: Jan 29, 2018

The read/write throughput is measured by read/write capacity units (CUs), which is the smallest billing unit for the data read and write operations.

One read CU indicates that 4 KB data is read from the table. One write CU indicates that 4 KB data is written into the table. Data smaller than 4 KB during the operation is rounded up to the nearest CU. For example, writing 7.6 KB data consumes two write CUs, and reading 0.1 KB data consumes one read CU.

When applications use an API to perform Table Store read/write operations, the corresponding amount of read/write CUs is consumed.

Reserved throughput

The reserved read/write throughput:

  • Is an attribute of a table.

    When creating a table, the application specifies the read/write throughput reserved for the table. Configuring the reserved read/write throughput does not affect the table’s access performance and service capability.

  • Can be set to zero.

    When the reserved read/write throughput is greater than zero, Table Store assigns and reserves enough resources for the table according to this configuration to guarantee low resource costs. The reserved read/write throughput of a table can be dynamically changed using the UpdateTable operation.

For a non-zero reserved read/write throughput, your Table Store service is billed even if no read and write requests are made. To guarantee billing accuracy, Table Store limits the maximum reserved read/write throughput to 5000 CUs per table (neither read throughput nor write throughput can exceed 5000 CUs). If you require more than 5000 CUs of reserved read/write throughput for a single table, open a ticket to increase the throughput.

The reserved read/write throughput of a non-existent table is regarded as zero. To access a non-existent table, one additional read CU or one additional write CU is consumed depending on the actual operation.

Additional throughput

The additional read/write throughput refers to the portion of the actual consumed read/write throughput that exceeds the reserved read/write throughput. Its statistical period is one second. For example, if the reserved read throughput of a table is set to 100 CUs and, within one second, the read operation actually consumes 120 CUs, then the additional read throughput consumed within the second is 20 CUs.

For the additional read/write throughput mode, it is difficult to estimate the amount of compute resources that need to be reserved for data tables. Table Store is required to provide sufficient service capability to effectively handle access traffic spikes. For this reason, the unit price of additional read/write throughput is higher than that of reserved read/write throughput. To make sure that low costs are maintained, we recommend that you set an appropriate value of the reserved read/write throughput.

Note: Because it is difficult to accurately reserve resources based on the additional read/write throughput, in extreme situations, Table Store may return an error OTSCapacityUnitExhausted to an application when an access to a single partition key consumes 10,000 CUs per second. In this case, policies, such as backoff retry, are used to reduce the frequency of access to the table.

For more information, see Table Store tables and billing methods.

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