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 are designed to prevent configurations that could negatively impact performance or availability.

Replication within regions

HCD databases replicate data across three availability zones within the launched region to promote uptime and ensure data integrity.

Limited functions and configurations

HCD databases have guardrails on certain functions and configurations to ensure high performance and availability.

The following table lists the limitations and notes for HCD databases:

Parameter Limit Notes

Large partition

Warning

A warning is issued if reading or compacting a partition that exceeds 100 MB.

Lists

Fixed

Cannot UPDATE or DELETE a list value by index because HCD does not allow list operations that perform a read-before-write.

UPDATE and DELETE operations that are not by index work normally.

Page size

Fixed

HCD configures the proper page size automatically.

User-defined functions (UDFs) and user-defined aggregate functions (UDAs)

Disabled

HCD does support UDFs and UDAs, but they must be enabled in the cassandra.yaml file.

Ignored values in CQL commands

If you try to use a CQL command with unsupported data definition language (DDL) properties, the command works, but ignores the unsupported values.

For example, the following CQL command creates a table with the nodesync attribute, which is not supported in HCD:

CREATE TABLE IF NOT EXISTS library.books
  (
    id UUID PRIMARY KEY,
    lastname text,
    firstname text)
  WITH nodesync={'enabled': 'true'};

The table is created with the defined attributes, except for the nodesync values. The results show a warning that lists the unsupported values, which are ignored:

Warnings :
The unsupported 'nodesync' table option was ignored.

Supported CQL commands

For a list of supported CQL commands, see the CQL quick reference.

Unsupported CQL commands

Operations concerning search indexes and row-level access control are not supported. This affects the following CQL commands, which are not supported in HCD:

CREATE SEARCH INDEX
DROP SEARCH INDEX
ALTER SEARCH INDEX CONFIG
ALTER SEARCH INDEX SCHEMA
COMMIT SEARCH INDEX
REBUILD SEARCH INDEX
RELOAD SEARCH INDEX
RESTRICT ROWS
UNRESTRICT ROWS