Hyper-Converged Database (HCD) guardrails
Hyper-Converged Database (HCD) is a self-managed database powered by Apache Cassandra®, an open-source NoSQL distributed database. To ensure high availability and optimum performance, HCD databases have guardrails on underlying Cassandra functionality. These guardrails prevent configurations that could negatively impact performance or availability.
To configure guardrails, see Guardrails configuration.
Startup warnings and failures
HCD issues warnings or prevents startup for certain configurations to maintain optimal performance and compatibility.
Startup warnings
The following configurations generate warnings at startup:
Parameter | Configuration location | Warns when |
---|---|---|
Non-murmur3 partitioner |
|
You use a partitioner other than murmur3. |
JBOD (multiple data directories) |
|
You configure multiple data directories. DataStax recommends using striped LVM instead. |
Non-BTI SSTable format |
Automatically configured by HCD |
You don’t use BTI SSTable format type.
This is automatically configured by HCD and cannot be changed in |
Materialized views enabled |
|
You set |
SASI indexes enabled |
|
You set |
COMPACT STORAGE tables |
Table-level setting |
COMPACT STORAGE tables are present in the database.
This is a table-level setting, not a |
COMPACT STORAGE table dropping enabled |
|
You enable the ability to drop COMPACT STORAGE tables. Instead, you must manually migrate such tables. |
Legacy secondary indexes |
Table-level setting and |
You enable legacy secondary indexes or if any tables use them.
This is a table-level setting and a |
High tombstone failure threshold |
|
You set |
High batch size failure threshold |
|
You set |
Startup failures
The following configurations cause HCD to fail to start:
Configuration | Description |
---|---|
HCD will fail to start if transient replication is enabled. |
Limited functions and configurations
The following table lists specific limitations and configurations for HCD databases:
Parameter | Limit | Notes |
---|---|---|
Large partition |
Warning |
Issues a warning when reading or compacting a partition that exceeds 100 MB. |
Page size |
Fixed |
HCD configures the proper page size automatically. |
User-defined functions (UDFs) and user-defined aggregate functions (UDAs) |
Disabled |
HCD supports UDFs and UDAs, but you must enable them in the |
List operations |
Enabled |
Read-before-write operations for lists are enabled by default.
Configured with |
Guardrails configuration
The following tables list the default guardrail thresholds by category:
Warning thresholds
Guardrail parameter | Default threshold | Warns when |
---|---|---|
|
1000 |
The tombstone count exceeds this threshold. |
|
100 |
The partition size exceeds 100 MB. |
|
64 |
The batch size exceeds 64 KB. |
|
10 |
The unlogged batch spans more than 10 partitions. |
|
-1 (unlimited) |
The vector dimensions exceed the threshold. |
|
10240 |
The collection size exceeds 10,240 KB (10 MB). |
|
200 |
The number of items per collection exceeds 200. |
|
100 |
The number of tables exceeds 100. |
|
10000 |
The |
|
70 |
The disk usage percentage exceeds 70%. |
Failure thresholds
Guardrail parameter | Default threshold | Fails when |
---|---|---|
|
-1 (unlimited) |
The column value size exceeds the threshold. |
|
200 |
The number of columns per table exceeds 200. |
|
100 |
The number of fields per UDT exceeds 100. |
|
8192 |
The vector dimensions exceed 8192. |
|
0 |
Any secondary indexes are created (not allowed). |
|
10 |
The number of SAI indexes per table exceeds 10. |
|
100 |
The total number of SAI indexes exceeds 100. |
|
0 |
Any SASI indexes are created (not allowed). |
|
4000 |
The SAI ANN rerank K value exceeds 4000. |
|
0 |
Any materialized views are created (not allowed). |
|
200 |
The number of tables exceeds 200. |
|
-1 (unlimited) |
The page size exceeds the threshold. |
|
25 |
The IN clause creates a Cartesian product exceeding 25. |
|
20 |
The number of partition keys in SELECT exceeds 20. |
|
-1 (unlimited) |
The disk usage percentage exceeds the threshold. |
|
-1 (unlimited) |
The disk usage exceeds the maximum disk size threshold in GB. |
|
20000 |
The |
|
-1 (unlimited) |
The number of query filters exceeds the warn threshold. |
|
-1 (unlimited) |
The number of query filters exceeds the fail threshold. |
|
ANY |
Disallows any write consistency level. |