AWS DynamoDB is a key-values database, every item in DynamoDB is associated an unique primary key which is required in almost all DynamoDB's APIs, so having a good design on this primary key is crucial for your development. What's primary key in DynamoDB A primary key is used to identity an item in DynamoDB uniquely.
What is primary key in DynamoDB?
In this blog post, we are going to discuss Primary Key in DynamoDB. When you create a table, in addition to the table name, you must specify the primary key of the table. The primary key uniquely identifies each item in the table, so that no two items can have the same key. A simple primary key, composed of one attribute known as the partition key.
What is partition key and sort key in DynamoDB?
Partition key and sort key – Also referred to as composite primary key, this key comprises of two attributes, namely, partition key and sort key.DynamoDB uses the partition key value as input to an internal hash function. The output from the hash function sets the partition in which the item will be stored.
What is a hash key in DynamoDB?
@Teofrostus, the hash key is used to identify the partition that contains the item (s). Without it, DynamoDB wouldn't which partition to look in. Not knowing where to look defeats a Query, and is the use case for a Scan (or Global Secondary Index, but that's not suitable for your use case of using nothing but a time series to select data).
How do I get the primary key of an item?
You have to specify the primary key of the item you want. In SQL, you use the SELECT statement to retrieve data from a table. You can request one or more columns in the result (or all of them, if you use the * operator).
What is a partition key in DynamoDB?
It is a simple primary key, composed of one attribute.DynamoDB utilizes the partition key’s value as input to an internal hash function. The output from that hash function sets the partition (physical storage internal to DynamoDB) where the item is to be stored. Table having only the partition key is not allowed to have more than one item with the same partition key value. For instance, look into the below-depicted table:#N#The People table has a simple primary key (PersonID). You can access any item in the People table directly by providing the PersonId value for that item.
What is a composite primary key?
Also referred to as composite primary key, this key comprises of two attributes, namely, partition key and sort key.DynamoDB uses the partition key value as input to an internal hash function. The output from the hash function sets the partition in which the item will be stored. Each item with the same partition key value are stored together, in sorted order by sort key value. In a table that has a partition key and a sort key, it’s allowed for two items to have the same partition key value assuming those items have different sort key values. for instance, look into the database of Music depicted below:#N#The Music table above is an example of a table with a composite primary key ( Artist and SongTitle ). You can access any item in the Music table directly, if you provide the Artist and SongTitle values for that item. A composite primary key provides users with additional flexibility when querying data. For example, if you provide only the value for Artist, DynamoDB retrieves all of the songs by that artist. To get only a subset of songs by a particular artist, you can provide a value for Artist along with a range of values for SongTitle.
What is composite key in music table?
The Music table above is an example of a table with a composite primary key (Artist and SongTitle). You can access any item in the Music table directly if you provide the Artist and SongTitle values for that item. A composite primary key provides users with additional flexibility when querying data. For example, if you provide only the value for Artist, DynamoDB retrieves all of the songs by that artist. To get only a subset of songs by a particular artist, you can provide a value for Artist along with a range of values for SongTitle.
Can two items have the same primary key?
No two-item can have the same primary key. In DynamoDB the primary key must be specified along with the table name while creating a table. DynamoDB supports two different kinds of primary keys: Partition key. Partition key and sort key.
Can you have more than one partition key?
Table having only the partition key is not allowed to have more than one item with the same partition key value. For instance, look into the below-depicted table: The People table has a simple primary key (PersonID). You can access any item in the People table directly by providing the PersonId value for that item.
PartiQL
DynamoDB provides the ExecuteStatement action for retrieving an item by its primary key using the SELECT statement.
Classic APIs
DynamoDB provides the GetItem action for retrieving an item by its primary key. GetItem is highly efficient because it provides direct access to the physical location of the item. (For more information, see Partitions and Data Distribution .)
What is composite primary key?
A composite primary key gives you additional flexibility when querying data. For example, if you provide only the value for Artist, DynamoDB retrieves all of the songs by that artist. To retrieve only a subset of songs by a particular artist, you can provide a value for Artist along with a range of values for SongTitle.
What is the primary key of a row?
This means that every row's primary key is the combination of the hash and range key. You can make direct gets on single rows if you have both the hash and range key, or you can make a query against the sorted range index.
Can you get multiple items with a primary key?
If you decide that your PrimaryKey is simply a hash key then great you can get a single item out of it. If you decide however that your primary key is hashKey + SortKey then you could also do a range query on your primary key because you will get your items by (HashKey + SomeRangeFunction (on range key)). So you can get multiple items with your primary key query.
Can a hashkey have multiple ranges?
So both have a different purpose and together help to do complex query. In the above example hashkey1 can have multiple n-range. Another example of range and hashkey is game, userA (hashkey) can play Ngame (range)
Can you get a single item out of a hash key?
If you decide that your PrimaryKey is simply a hash key then great you can get a single item out of it. If you decide however that your primary key is hashKey + SortKey then you could also do a range query on your primary key because you will get your items by (HashKey + SomeRangeFunction(on range key)).
A brief introduction to partition keys
To better understand how to organize your data, it’s important to understand how data is stored in DynamoDB. Each item in a DynamoDB table requires that you create a primary key for the table, as described in the DynamoDB documentation. A primary key can be a partition key or a combination of a partition key and sort key.
Using sort keys to extend data retrieval options
In some cases, you might supply only a partition key as the primary key when creating a table. In these cases, you’re limited to data retrieval by the partition key or by returning all items in a table with the scan operation. Creating a table this way is simple, and in some cases, simple is all you need.
Working with ranges
You use ranges with sort keys to create queries. The following operators are available with the KeyConditionExpressions query:
How to use sort keys for data organization and retrieval
Applying the knowledge of sort keys to real-life examples highlights repeatable techniques and patterns that you can use for data organization and retrieval in tables you create in the future.
Summary
Sort keys can add more power to the querying capabilities of DynamoDB. However, you must use some forethought. Remember to employ string templates that take advantage of the begins_with operator and to order the string by least specific data to most specific.
What is the primary key in a table?
The primary key uniquely identifies each item in the table, so that no two items can have the same key.
How does DynamoDB work?
DynamoDB uses the partition key value as input to an internal hash function. The output from the hash function determines the partition (physical storage internal to DynamoDB) in which the item will be stored. All items with the same partition key value are stored together, in sorted order by sort key value.
What is partition key?
Partition key: A simple primary key, composed of one attribute known as the partition key. DynamoDB uses the partition key’s value as input to an internal hash function. The output from the hash function determines the partition (physical storage internal to DynamoDB) in which the item will be stored. In a table that has only a partition key, no ...
Can you query a table with a non primary key?
Note: We are unable to query the table as the country is not part of the primary key. To query using a non-primary key, we need to create a secondary index on the table which will be covered in the next blog post.
Does DynamoDB sort in order?
Observe: Data is not sorted in any order. Because we have created a simple primary key on id, DynamoDB has not sorted the data in any order. In order to sort the data, we have to create a composite primary key and define the sort key.
What is the primary key in DynamoDB?
The Primary Key in DynamoDB must be unique so that it can find the exact item in the table. DynamoDB supports two kinds of Primary Keys: Hash Type Primary Key: If an attribute uniquely identifies an item, it can be considered as Primary. DynamoDB builds a hash index on the attribute to facilitate the uniqueness.
What is DynamoDB?
Here are ten key features that helped make Amazon DynamoDB into a giant. 1. Amazon DynamoDB is a managed, NoSQL database service. With a managed service, users only interact with the running application itself. You don’t need to worry about things like server health, storage, and network connectivity.
How many GSIs can DynamoDB support?
GSIs span multiple partitions and are placed in separate tables. DynamoDB supports up to five GSIs. While creating a GSI, you need to carefully choose your hash key because that key will be used for partitioning.
Why is DynamoDB a giant?
In this post, I’m going to focus on Amazon DynamoDB — the giant of the NoSQL world. I believe it’s become a giant because AWS built it for their own operations. Considering how much was at stake financially, anything less than complete reliability would simply not be tolerated. Software created in such a demanding environment and with the use of AWS-scale resources is bound to be epic. The result? Fantastic reliability and durability, with blazing fast service.
What is DynamoDB managed service?
With a managed service, users only interact with the running application itself. You don’t need to worry about things like server health, storage, and network connectivity. With Amazon DynamoDB, AWS provisions and runs the infrastructure for you. Some of DynamoDB’s critical managed infrastructure features include: 1 Automatic data replication over three availability-zones in a single region. 2 Infinitely scalable read-write I/O running on IOPS-optimized solid state drives. 3 A provisioned-throughput model where read and write units can be adjusted at any time based on actual application usage. 4 Data backed up to S3. 5 Integrated with other AWS services like Elastic MapReduce (EMR), Data Pipeline, and Kinesis. 6 Pay-per-use model – you never pay for hardware or services you’re not actually using. 7 Security and access control can be applied using Amazon’s IAM service. 8 Great enterprise-ready features such as a robust SLA, monitoring tools, and private VPN functionality.
Is Amazon DynamoDB scalable?
That makes DynamoDB a highly available, scalable, and distributed data store. Here are ten key features that helped make Amazon DynamoDB into a giant. 1.
Is Amazon DynamoDB a good NoSQL service?
With DynamoDB, Amazon has done a great job providing a NoSQL service with strong consistency and predictable performance, while saving users from the complexities of a distributed system. One proof of their success is the many systems (like Riak) that chose to build on the DynamoDB design. With a strong ecosystem, Amazon DynamoDB is something to consider when you are building your next Internet-based scale application.
