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DynamoDB and Hash Key
If a specific hash key element has a large range key element set, and the results cannot be retrieved in a single Query request, the ExclusiveStartKey continuation parameter allows you to submit a new query request from the last retrieved item without re-processing the data already retrieved.
Pagination, LastEvaluatedKey, and ExclusiveStartKey
DynamoDB paginates the results from Query and Scan operations. With pagination,
Query and Scan results are divided into distinct pieces; an application can process the first page of results, then the second page, and so on. The data returned from a Query or Scan operation is limited to 1 MB; this means that if you scan a table that has more than 1 MB of data, you'll need to perform another Scan operation to continue to the next 1 MB of data in the table.
If you query for specific attributes that match values that amount to more than 1 MB of data, you'll need to perform another Query request for the next 1 MB of data. The second query request uses a starting point (ExclusiveStartKey) based on the key of the last returned value (LastEvaluatedKey) so you can progressively query or scan for new data in 1 MB increments.
When the entire result set from a Query or Scan has been processed, the LastEvaluatedKey is null.
This indicates that the result set is complete (i.e. the operation processed the last page of data).
If LastEvaluatedKey is anything other than null, this does not necessarily mean that there is more data in the result set. The only way to know when you have reached the end of the result set is when LastEvaluatedKey is null.
A Scan result is an eventually consistent read, meaning that changes to data immediately before the scan takes place might not be included in the scan results. The result set will not contain any duplicate items.
A Query result is an eventually consistent read, but you can optionally request a strongly consistent read instead. An eventually consistent read might not reflect the results of a recently completed PutItem or UpdateItem operation
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