[CASSANDRA-14572] Expose all table metrics in virtual table

• Type: New Feature
• Status: Resolved
• Priority: Low
• Resolution: Fixed
• Fix Version/s: 5.1
• Component/s: Legacy/Observability, Observability/Metrics
• Labels: virtual-tables

Source Control Link

https://github.com/apache/cassandra/commit/2e7def7626fe299318e0cf4c2bf8138a6c31e149

Test and Documentation Plan

Run full CI, additionally manually verify all metrics table via cqlsh

• Assignee: Maxim Muzafarov
• Reporter: Chris Lohfink

Authors

Maxim Muzafarov

Reviewers

Chris Lohfink, Stefan Miklosovic

• Created: 17/Jul/18 17:23
• Updated: 24/May/24 19:49
• Resolved: 03/Apr/24 18:13

Description

While we want a number of virtual tables to display data in a way thats great and intuitive like in nodetool. There is also much for being able to expose the metrics we have for tooling via CQL instead of JMX. This is more for the tooling and adhoc advanced users who know exactly what they are looking for.

Schema:
Initial idea is to expose data via ((keyspace, table), metric) with a column for each metric value. Could also use a Map or UDT instead of the column based that can be a bit more specific to each metric type. To that end there can be a metric_type column and then a UDT for each metric type filled in, or a single value with more of a Map<Text, Text> style. I am purposing the column type though as with ALLOW FILTERING it does allow more extensive query capabilities.

Implementations:

• Use reflection to grab all the metrics from TableMetrics (see: CASSANDRA-7622 impl). This is easiest and least abrasive towards new metric implementors... but its reflection and a kinda a bad idea.
• Add a hook in TableMetrics to register with this virtual table when registering
• Pull from the CassandraMetrics registery (either reporter or iterate through metrics query on read of virtual table)

Issue Links

• is related to: CASSANDRA-11994 Expose metrics via CQL interface
• is related to: CASSANDRA-18238 Implicitly enable ALLOW FILTERING on virtual tables
• is related to: CASSANDRA-14629 Abstract Virtual Table for very large result sets
• is related to: CASSANDRA-19150 Align values in rows in CQLSH right for numbers, left for text
• relates to: CASSANDRA-19567 Minimize the heap consumption when registering metrics
• links to: dev-list: [DISCUSSION] Framework for Internal Collection Exposure
• links to: GitHub Pull Request #3152
• links to: GitHub PullRequest dtest #249