Remember that the throughput is per item, not per query. For instance we have an indexed query that returns ~1500 rows each time. Just doing that query a couple of times per second would create that kind of throughput requirement.
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If your items are less than 1KB in size, then each unit of Read Capacity will give you 1 read/second of capacity and each unit of Write Capacity will give you 1 write/second of capacity. For example, if your items are 512 bytes and you need to read 100 items per second from your table, then you need to provision 100 units of Read Capacity.
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Looks like 1KB is the minimum for calculations.
This is currently an undocumented benefit of the query operation, but we will be adding that to our documentation shortly.