Functional differences: Amazon Keyspaces vs. Apache Cassandra

The following are the functional differences between Amazon Keyspaces and Apache Cassandra.

Apache Cassandra APIs, operations, and data types

Amazon Keyspaces supports all commonly used Cassandra data-plane operations, such as creating keyspaces and tables, reading data, and writing data. To see what is currently supported, see Supported Cassandra APIs, operations, functions, and data types in Amazon Keyspaces.

Asynchronous creation and deletion of keyspaces and tables

Amazon Keyspaces performs data definition language (DDL) operations, such as creating and deleting keyspaces and tables, asynchronously. To learn how to monitor the creation status of resources, see Creating keyspaces in Amazon Keyspaces and Creating tables in Amazon Keyspaces. For a list of DDL statements in the CQL language reference, see DDL statements (data definition language) in Amazon Keyspaces.

Authentication and authorization

Amazon Keyspaces (for Apache Cassandra) uses AWS Identity and Access Management (IAM) for user authentication and authorization, and supports the equivalent authorization policies as Apache Cassandra. As such, Amazon Keyspaces does not support Apache Cassandra's security configuration commands.

Batch

Amazon Keyspaces supports unlogged batch commands with up to 30 commands in the batch. Only unconditional INSERT, UPDATE, or DELETE commands are permitted in a batch. Logged batches are not supported.

Cluster configuration

Amazon Keyspaces is serverless, so there are no clusters, hosts, or Java virtual machines (JVMs) to configure. Cassandra’s settings for compaction, compression, caching, garbage collection, and bloom filtering are not applicable to Amazon Keyspaces and are ignored if specified.

Connections

You can use existing Cassandra drivers to communicate with Amazon Keyspaces, but you need to configure the drivers differently. Amazon Keyspaces supports up to 3,000 CQL queries per TCP connection per second, but there is no limit on the number of connections a driver can establish.

Most open-source Cassandra drivers establish a connection pool to Cassandra and load balance queries over that pool of connections. Amazon Keyspaces exposes 9 peer IP addresses to drivers, and the default behavior of most drivers is to establish a single connection to each peer IP address. Therefore, the maximum CQL query throughput of a driver using the default settings is 27,000 CQL queries per second.

To increase this number, we recommend increasing the number of connections per IP address your driver is maintaining in its connection pool. For example, setting the maximum connections per IP address to 2 doubles the maximum throughput of your driver to 54,000 CQL queries per second.

As a best practice, we recommend configuring drivers to use 500 CQL queries per second per connection to allow for overhead and to improve distribution. In this scenario, planning for 18,000 CQL queries per second requires 36 connections. Configuring the driver for 4 connections across 9 endpoints provides for 36 connections performing 500 request per second. For more information about best practices for connections, see Client driver connections to Amazon Keyspaces (for Apache Cassandra).

When connecting with VPC endpoints, there might be fewer endpoints available. This means that you have to increase the number of connections in the driver configuration. For more information about best practices for VPC connections, see How to configure connections over VPC endpoints in Amazon Keyspaces.

IN keyword

Amazon Keyspaces supports the IN keyword in the SELECT statement. IN is not supported with UPDATE and DELETE. When using the IN keyword in the SELECT statement, the results of the query are returned in the order of how the keys are presented in the SELECT statement. In Cassandra, the results are ordered lexicographically.

When using ORDER BY, full re-ordering with disabled pagination is not supported and results are ordered within a page. Slice queries are not supported with the IN keyword. TOKENS are not supported with the IN keyword. Amazon Keyspaces processes queries with the IN keyword by creating subqueries. Each subquery counts as a connection towards the 3,000 CQL queries per TCP connection per second limit. For more information, see Using the IN operator with the SELECT Statement in Amazon Keyspaces.

CQL query throughput tuning

Amazon Keyspaces supports up to 3,000 CQL queries per TCP connection per second, but there is no limit on the number of connections a driver can establish.

Most open-source Cassandra drivers establish a connection pool to Cassandra and load balance queries over that pool of connections. Amazon Keyspaces exposes 9 peer IP addresses to drivers, and the default behavior of most drivers is to establish a single connection to each peer IP address. Therefore, the maximum CQL query throughput of a driver using the default settings will be 27,000 CQL queries per second.

To increase this number, we recommend increasing the number of connections per IP address your driver is maintaining in its connection pool. For example, setting the maximum connections per IP address to 2 will double the maximum throughput of your driver to 54,000 CQL queries per second.

FROZEN collections

The FROZEN keyword in Cassandra serializes multiple components of a collection data type into a single immutable value that is treated like a BLOB. INSERT and UPDATE statements overwrite the entire collection.

Amazon Keyspaces supports up to five levels of nesting for frozen collections by default. For more information, see Amazon Keyspaces service quotas.

Amazon Keyspaces doesn't support inequality comparisons that use the entire frozen collection in a conditional UPDATE or SELECT statement. The behavior for collections and frozen collections is the same in Amazon Keyspaces.

When you're using frozen collections with client-side timestamps, in the case where the timestamp of a write operation is the same as the timestamp of an existing column that isn't expired or tombstoned, Amazon Keyspaces doesn't perform comparisons. Instead, it lets the server determine the latest writer, and the latest writer wins.

For more information about frozen collections, see Collection types.

Lightweight transactions

Amazon Keyspaces (for Apache Cassandra) fully supports compare and set functionality on INSERT, UPDATE, and DELETE commands, which are known as lightweight transactions (LWTs) in Apache Cassandra. As a serverless offering, Amazon Keyspaces (for Apache Cassandra) provides consistent performance at any scale, including for lightweight transactions. With Amazon Keyspaces, there is no performance penalty for using lightweight transactions.

Load balancing

The system.peers table entries correspond to Amazon Keyspaces load balancers. For best results, we recommend using a round robin load-balancing policy and tuning the number of connections per IP to suit your application's needs.

Pagination

Amazon Keyspaces paginates results based on the number of rows that it reads to process a request, not the number of rows returned in the result set. As a result, some pages might contain fewer rows than you specify in PAGE SIZE for filtered queries. In addition, Amazon Keyspaces paginates results automatically after reading 1 MB of data to provide customers with consistent, single-digit millisecond read performance. For more information, see Paginating results in Amazon Keyspaces.

Partitioners

The default partitioner in Amazon Keyspaces is the Cassandra-compatible Murmur3Partitioner. In addition, you have the choice of using either the Amazon Keyspaces DefaultPartitioner or the Cassandra-compatible RandomPartitioner.

With Amazon Keyspaces, you can safely change the partitioner for your account without having to reload your Amazon Keyspaces data. After the configuration change has completed, which takes approximately 10 minutes, clients will see the new partitioner setting automatically the next time they connect. For more information, see Working with partitioners in Amazon Keyspaces.

Prepared statements

Amazon Keyspaces supports the use of prepared statements for data manipulation language (DML) operations, such as reading and writing data. Amazon Keyspaces does not currently support the use of prepared statements for data definition language (DDL) operations, such as creating tables and keyspaces. DDL operations must be run outside of prepared statements.

Range delete

Amazon Keyspaces supports deleting rows in range. A range is a contiguous set of rows within a partition. You specify a range in a DELETE operation by using a WHERE clause. You can specify the range to be an entire partition.

Furthermore, you can specify a range to be a subset of contiguous rows within a partition by using relational operators (for example, '>', '<'), or by including the partition key and omitting one or more clustering columns. With Amazon Keyspaces, you can delete up to 1,000 rows within a range in a single operation. Additionally, range deletes are atomic, but not isolated.

System tables

Amazon Keyspaces populates the system tables that are required by Apache 2.0 open-source Cassandra drivers. The system tables that are visible to a client contain information that's unique to the authenticated user. The system tables are fully controlled by Amazon Keyspaces and are read-only.

Read-only access to system tables is required, and you can control it with IAM access policies. For more information, see Managing access using policies. You must define tag-based access control policies for system tables differently depending on whether you use the AWS SDK or Cassandra Query Language (CQL) API calls through Cassandra drivers and developer tools. To learn more about tag-based access control for system tables, see Amazon Keyspaces resource access based on tags.

If you access Amazon Keyspaces using Amazon VPC endpoints, you see entries in the system.peers table for each Amazon VPC endpoint that Amazon Keyspaces has permissions to see. As a result, your Cassandra driver might issue a warning message about the control node itself in the system.peers table. You can safely ignore this warning.

Timestamps

In Amazon Keyspaces, cell-level timestamps that are compatible with the default timestamps in Apache Cassandra are an opt-in feature.

The USING TIMESTAMP clause and the WRITETIME function are only available when client-side timestamps are turned on for a table. To learn more about client-side timestamps in Amazon Keyspaces, see Working with client-side timestamps in Amazon Keyspaces.