Global secondary index in DynamoDb – An index with a partition key and a sort key that can be different from the base table. A global secondary index is very helpful when you need to query your data without primary key.
The primary key of a global secondary index can be partition key or composite (partition key and sort key).
Global secondary indexes can be created at the same time that you create a table. You can also add a new global secondary index to an existing table, or delete an existing global secondary index
A global secondary index lets you query over the entire table, across all partitions.
The index partition key and sort key (if present) can be any base table attributes of type string, number, or binary.
With global secondary index queries or scans, you can only request the attributes that are projected into the index. DynamoDB will not fetch any attributes from the table.
There are no size restrictions for global secondary indexes.
Click through to learn more about these as well as local secondary indexes.