Global Secondary Index Considerations
If a query exceeds the provisioned read capacity of a global secondary index, that request will be throttled. Similarly, if a request performs heavy write activity on the table, but a global secondary index on that table has insufficient write capacity, then the write activity on the table will be throttled.
Tip
For a table write to succeed, the provisioned throughput settings for the table and global secondary indexes must have enough write capacity to accommodate the write; otherwise, the write will be throttled.
Global secondary indexes support eventually consistent reads, each of which consume one half of a read capacity unit. The number of read capacity units is the sum of all projected attribute sizes across all of the items returned in the index query results. With write activities, the total provisioned throughput cost for a write, consists of the sum of write capacity units consumed by writing to the table and those consumed by updating the global secondary indexes.
