AWS DynamoDB Query based on non-primary keys

Question

I'm new to AWS DynamoDB and wanted to clarify something. Is it possible to query a table and filter base on a non-primary key attribute. My table looks like the following

Store Id: PrimaryKey Name: simple string Location: simple string

Now I want to query on the Name, but I think I have to give the key as well from what I know? Apart from that I can use the scan but then I will be loading all the data.

Answer 1

From the docs:

The Query operation finds items based on primary key values. You can query any table or secondary index that has a composite primary key (a partition key and a sort key).

DynamoDB requires queries to always use the partition key.

In your case your options are:

• create a Global Secondary Index that uses Name as a primary key
• use a Scan + Filter if the table is relatively small, or if you expect the result set will include the majority of the records in the table

Answer 2

There are few designs principals that you can follow while you are using DynamoDB. If you are coming from a relational background, you have already witnessed the query limitations from primary key attributes.

• Design your tables, for querying and separating hot and cold data.
• Create Indexes for Querying from Non Key attributes (You have two options, Global Secondary Index which you can define at any time and Local Secondary Index which you need to specify at table creation time).

With the Global Secondary Index you can promote any NonKey attribute as the Partition Key for the Index and select another attribute for Sort Key for querying. For Local Secondary Index, you can promote any Non Key attribute as the Sort Key keeping the same Partition Key.

• Using Indexes for query is important also to improve the efficiency in using provisioned throughput.
• Although having indexes consumes the read throughput from the table, it also saves read through put from in a way that, if you project the right amount of attributes to read, it can give a huge benefit in reading. Check the following example.

Lets say you have a DynamoDB table that has items of 40KB. If you read directly from the table to list 10 items, it consumes 100 Read Throughput Units (For one item 10 Units since one unit can read 4KB and multiply it by 10). If you have an index defined just to project the attributes needed to list which will be having 4KB per item, then it will be consuming only 10 Read Throughput Units(One Unit per item) which makes a huge difference in terms of cost.

• With DynamoDB its really important how you define Indexes to optimize for Querying not only from Query capability but also in terms of throughput.

Answer 3

You can not query based non-primary key attribute in Dynamo Db.

If you wanted to still do that you can do it using scan query,but scan is costly operation in DyanmoDB and if table is large, then it will affect performance and not recommended because it will scan each item in table and AWS cost you for all item it scan for that query.

There are two ways to achieve it

1. Keep Store Id as your PrimaryKey/ Partaion key of Dyanmo DB table and add Name/Location as sort Key (only one as Dyanmo DB accept only one Attribute as sort key by design.
2. Create Global Secondary Indexes for Querying from Non Key attributes which you are more frequenly required.

There are 3 ways to created GSI in Dyanamo DB, In your case select GSI with option INCLUDE and add Name , Location and store ID in Idex.

• KEYS_ONLY – Each item in the index consists only of the table partition key and sort key values, plus the index key values. The KEYS_ONLY option results in the smallest possible secondary index.

• INCLUDE – In addition to the attributes described in KEYS_ONLY, the secondary index will include other non-key attributes that you specify.

• ALL – The secondary index includes all of the attributes from the source table. Because all of the table data is duplicated in the index, an ALL projection results in the largest possible secondary index.