DynamoDB GSI vs. LSI

Updated 2024-09-19

AWS has a good video on how to choose between GSI and LSI that also covers their internal differences.

Highlights:

• GSI
  • Eventually consistent because it is implemented as a shadow table that receives updates from the original table
  • Can use any primary key and sort key
• LSI
  • Strongly consistent because the data comes from the original table
  • Can use any sort key but always uses the table's original primary key

Original content

Are you struggling to understand the difference between a DynamoDB Global Secondary Index (GSI) and a Local Secondary Index (LSI)?

A true legend wrote it up on Stack Overflow concisely:

Global secondary index — an index with a hash and range key
that can be different from those on the table. A global
secondary index is considered "global" because queries on
the index can span all of the data in a table, across all
partitions.

Local secondary index — an index that has the same hash key
as the table, but a different range key. A local secondary
index is "local" in the sense that every partition of a
local secondary index is scoped to a table partition that
has the same hash key.

Remember:

• Local == Same hash key, so it refers to data in the same partition
• Global == Any hash key, so it can refer to data in any partition