Supported Apache Cassandra read and write consistency levels and associated costs
The topics in this section describe which Apache Cassandra consistency levels are supported for read and write operations in Amazon Keyspaces (for Apache Cassandra).
Write consistency levels
Amazon Keyspaces replicates all write
operations three times across multiple Availability Zones for durability and high
availability. Writes are durably stored before they are acknowledged using the
LOCAL_QUORUM
consistency level. For each 1 KB write, you are billed 1
write capacity unit (WCU) for tables using provisioned capacity mode or 1 write request unit (WRU)
for tables using on-demand mode.
You can use cqlsh
to set the consistency for all queries in the current
session to LOCAL_QUORUM
using the following code.
CONSISTENCY LOCAL_QUORUM;
To configure the consistency level programmatically, you can set the consistency with
the appropriate Cassandra client drivers. For example, the 4.x version Java drivers allow you
to set the consistency level in the app config
file as shown
below.
basic.request.consistency = LOCAL_QUORUM
If you're using a 3.x version Java Cassandra driver, you can specify the consistency level for the session by adding
.withQueryOptions(new QueryOptions().setConsistencyLevel(ConsistencyLevel.LOCAL_QUORUM)
as shown in the following
code example.
Session session = Cluster.builder() .addContactPoint(endPoint) .withPort(portNumber) .withAuthProvider(new SigV4AuthProvider("us-east-2")) .withSSL() .withQueryOptions(new QueryOptions().setConsistencyLevel(ConsistencyLevel.LOCAL_QUORUM) .build() .connect();
To configure the consistency level for specific write operations, you can define the consistency
when you call QueryBuilder.insertInto
with a setConsistencyLevel
argument
when you're using the Java driver.
Read consistency levels
Amazon Keyspaces supports three read
consistency levels: ONE
, LOCAL_ONE
, and LOCAL_QUORUM
. During a
LOCAL_QUORUM
read, Amazon Keyspaces returns a response reflecting the most recent updates
from all prior successful write operations. Using the consistency level ONE
or LOCAL_ONE
can improve the performance and availability of your read requests, but the response might not reflect the results of a
recently completed write.
For each 4 KB read using ONE
or LOCAL_ONE
consistency,
you are billed 0.5 read capacity units (RCUs) for tables using provisioned capacity mode
or 0.5 read request units (RRUs) for tables using on-demand mode. For each 4 KB read
using LOCAL_QUORUM
consistency, you are billed 1 read capacity unit (RCU)
for tables using provisioned capacity mode or 1 read request units (RRU) for tables
using on-demand mode.
Billing based on read consistency and read capacity throughput mode per table for
each 4 KB of reads | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Consistency level | Provisioned | On-demand | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
ONE |
0.5 RCUs | 0.5 RRUs | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
LOCAL_ONE |
0.5 RCUs | 0.5 RRUs | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
LOCAL_QUORUM |
1 RCU | 1 RRU |
To specify a different consistency for read operations, call
QueryBuilder.select
with a setConsistencyLevel
argument
when you're using the Java driver.
Unsupported consistency levels
The following consistency levels are not supported by Amazon Keyspaces and will result in exceptions.
Unsupported consistency levels | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Apache Cassandra | Amazon Keyspaces | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
EACH_QUORUM |
Not supported | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
QUORUM |
Not supported | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
ALL
|
Not supported | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
TWO |
Not supported | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
THREE |
Not supported | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
ANY |
Not supported | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
SERIAL |
Not supported | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
LOCAL_SERIAL |
Not supported |