Database limits
Astra DB Serverless is a fully managed serverless database-as-a-service (DBaaS), powered by Apache Cassandra®, an open-source NoSQL distributed database. To ensure high availability and optimum performance, Astra DB Serverless databases have guardrails on underlying Cassandra functionality.
Replicas
Astra DB Serverless replicates data across three availability zones within each deployed region to promote uptime and ensure data integrity.
By default, each database is deployed to a single region, and you can deploy databases to additional regions.
Astra DB follows the eventual consistency model, and you cannot independently manage, restrict, or modify replicas. When you insert data into an Astra DB database, it is eventually replicated across all of the database’s replicas, regardless of the original region where you loaded the data.
For multi-region databases, it can take time to replicate data across all regions. For more information, see Data consistency in multi-region databases.
Consistency levels
The Data API and clients always use the LOCAL_QUORUM consistency level for reads and writes.
With CQL and drivers, you can use all read consistency levels and all write consistency levels except ONE, ANY, and LOCAL_ONE.
LOCAL_QUORUM is generally sufficient for balanced workloads due to Astra DB’s eventual consistency model.
It has lower latency than multi-region consistency levels because it only requires acknowledgement from replicas in the target read/write region.
For more information about consistency levels, see the CQL documentation on CONSISTENCY and Data consistency in multi-region databases.
Table limits
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A Serverless (Vector) database can have up to 50 tables.
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For multi-region databases, the Astra Portal’s Data Explorer accesses and manipulates keyspaces, collections, tables, and data from the primary region. If you need to manage your database from a secondary region, you must use the Data API or CQL. Generally, accessing secondary regions is for latency optimization when the primary region is geographically distant from the caller or when the primary region is experiencing an outage. However, because multi-region databases follow an eventual consistent model, changes to data in any region are eventually replicated to the database’s other regions.
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A single value in a column/row cannot exceed 10MB of data.
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Only the
UnifiedCompactionStrategycompaction strategy is allowed. This strategy combines ideas fromSizeTieredCompactionStrategy,LeveledCompactionStrategy, andTimeWindowCompactionStrategy, along with token range sharding. This all-inclusive compaction strategy works well for Astra DB Serverless use cases. -
A warning is issued when reading or compacting a partition that exceeds 100MB.
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You cannot
UPDATEorDELETEa list value by index because Astra DB Serverless does not allow list operations that perform a read-before-write. Operations that are not by index work normally. -
Data API limits apply when inserting data into tables with the Data API.
Collection limits
The following limits apply to collections in Serverless (Vector) databases:
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Serverless (Vector) databases created after June 24, 2024 can have approximately 10 collections. Databases created before this date can have approximately 5 collections. The collection limit is based on the number of indexes.
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For multi-region databases, the Astra Portal’s Data Explorer accesses and manipulates keyspaces, collections, tables, and data from the primary region. If you need to manage your database from a secondary region, you must use the Data API or CQL. Generally, accessing secondary regions is for latency optimization when the primary region is geographically distant from the caller or when the primary region is experiencing an outage. However, because multi-region databases follow an eventual consistent model, changes to data in any region are eventually replicated to the database’s other regions.
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A collection cannot have more than 64 fields, as extracted from all documents inserted into the collection.
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Data API limits apply when inserting documents into collections, either through the Astra Portal or the Data API.
Index limits
There is a limit to the number of indexes you can have:
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A database created before June 24, 2024 can have up to 50 indexes (approximately 5 collections).
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A database created after June 24, 2024 can have up to 100 indexes (approximately 10 collections).
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A single collection in a database can have up to 10 indexes.
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This limit doesn’t apply to tables.
For more information, see Indexes in collections.
Rate limits
The default Astra DB Serverless rate limit is approximately 12,000 operations per second (ops/sec). Batches count as a single operation, regardless of the number of operations in a batch.
Astra DB Serverless workloads can be limited to 4,096 ops/sec for new or idle database when traffic suddenly increases suddenly. If you expect a sudden increase in traffic for an idle database, try to warm up your database before the workload increases. Make sure your database is active, and then send requests to your database to gradually increase the workload to the desired level over a period of time.
For production databases that require consistent capacity for traffic spikes, consider Provisioned Capacity Units for Astra DB Serverless.
If you encounter rate limiting exceptions or errors, you might need to allow some time for the database to scale up before retrying your request. Alternatively, you can use programmatic strategies to balance and retry workloads, such as request batching, generic retry policies, and retry policies with backoff strategies. How you implement these strategies depends on your chosen connection method and use case.
Data API limits
For information about Data API limits, see Data API limits.
CQL limits
For information about guardrails and limits for CQL commands, see Cassandra Query Language (CQL) for Astra DB.
Free plans
In addition to the limits described elsewhere on this page, organizations on the Free plan have the following additional limits:
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No more than five databases.
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Inactive databases are automatically hibernated and scheduled for deletion. For more information, see Database statuses: Hibernated.
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Cannot export metrics.
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Cannot use premium features, such as custom domains and multi-region databases.
To increase or remove these limits, upgrade your plan.
Cassandra configuration properties
The cassandra.yaml file is not configurable for Astra DB Serverless databases.
This file is defined as follows:
# Read requests
in_select_cartesian_product_failure_threshold: 25
partition_keys_in_select_failure_threshold: 20
tombstone_warn_threshold: 1000
tombstone_failure_threshold: 100000
# Write requests
batch_size_warn_threshold_in_kb: 64
batch_size_fail_threshold_in_kb: 640
unlogged_batch_across_partitions_warn_threshold: 10
user_timestamps_enabled: true
column_value_size_failure_threshold_in_kb: 5 * 2048L
read_before_write_list_operations_enabled: false
max_mutation_size_in_kb: 16384
write_consistency_levels_disallowed: ANY, ONE, LOCAL_ONE
# Schema
fields_per_udt_failure_threshold: 60
collection_size_warn_threshold_in_kb: 5 * 1024L
items_per_collection_warn_threshold: 20
columns_per_table_failure_threshold: 75
tables_warn_threshold: 100
tables_failure_threshold: 200
# SAI indexes failure threshold
sai_indexes_per_table_failure_threshold: 10
sai_indexes_total_failure_threshold: 100 # 50 for databases created before June 24, 2024The limits defined in cassandra.yaml inform the limits described elsewhere on this page.
