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AxonOps Cache Dashboard Metrics Mapping

This document maps the metrics used in the AxonOps Cache dashboard.

Dashboard Overview

The Cache dashboard monitors Cassandra's caching layers including KeyCache, RowCache, and CounterCache. These caches improve read performance by storing frequently accessed data in memory. The dashboard helps optimize cache configuration and monitor cache effectiveness.

Metrics Mapping

Cache Metrics (Applied to all cache types)

Dashboard Metric Description Attributes
cas_Cache_HitRate Cache hit ratio (0.0-1.0) scope (KeyCache/RowCache/CounterCache), dc, rack, host_id
cas_Cache_Size Current cache size in bytes scope, dc, rack, host_id
cas_Cache_Capacity Maximum cache capacity in bytes scope, dc, rack, host_id
cas_Cache_Entries Number of entries in cache scope, dc, rack, host_id
cas_Cache_Requests Total cache requests scope, dc, rack, host_id

Cache Types

KeyCache

  • Caches partition index entries
  • Enabled by default in Cassandra
  • Reduces disk seeks for finding partition locations

RowCache

  • Caches entire rows of data
  • Disabled by default due to memory overhead
  • Useful for small, hot datasets

CounterCache

  • Caches counter column values
  • Improves counter read performance
  • Only applies to counter columns

Query Examples

KeyCache Hit Rate

cas_Cache_HitRate{scope='KeyCache',dc=~'$dc',rack=~'$rack',host_id=~'$host_id'}

KeyCache Size by Group

sum(cas_Cache_Size{scope='KeyCache',dc=~'$dc',rack=~'$rack',host_id=~'$host_id'}) by ($groupBy)

KeyCache Requests per Second

sum(cas_Cache_Requests{axonfunction='rate',scope='KeyCache',dc=~'$dc',rack=~'$rack',host_id=~'$host_id'}) by ($groupBy)

RowCache Entries Count

sum(cas_Cache_Entries{scope='RowCache',dc=~'$dc',rack=~'$rack',host_id=~'$host_id'}) by ($groupBy)

CounterCache Capacity

sum(cas_Cache_Capacity{scope='CounterCache',dc=~'$dc',rack=~'$rack',host_id=~'$host_id'}) by ($groupBy)

Panel Organization

Key Cache Section

  • KeyCache HitRate Per Node - Line chart showing cache hit effectiveness (0-1 scale)

  • KeyCache Size - Line chart showing memory used by cache

  • KeyCache Capacity - Line chart showing maximum cache size

  • KeyCache Number of Entries - Line chart showing entry count

  • KeyCache Requests Count Per Second - Line chart showing request rate

Row Cache Section

  • RowCache Size - Line chart showing memory used

  • RowCache Capacity - Line chart showing maximum size

  • RowCache Number of Entries - Line chart showing entry count

  • RowCache Requests Count Per Second - Line chart showing request rate

Counter Cache Section

  • CounterCache HitRate - Line chart showing hit ratio

  • CounterCache Size - Line chart showing memory used

  • CounterCache Capacity - Line chart showing maximum size

  • CounterCache Number of Entries - Line chart showing entry count

  • CounterCache Requests Count Per Second - Line chart showing request rate

Filters

  • data center (dc) - Filter by data center

  • rack - Filter by rack

  • node (host_id) - Filter by specific node

  • groupBy - Dynamic grouping by dc, rack, or host_id

Metric Aggregation

The dashboard uses the groupBy variable for flexible aggregation: - Group by data center to see cache usage per DC - Group by rack for rack-level analysis - Group by host_id for node-level details

Legend format: - Size metrics: size_$groupBy - Capacity metrics: capacity_$groupBy - Other metrics: $groupBy

Important Notes

Hit Rate Interpretation:

  • Value between 0.0 and 1.0 (shown as percentunit)
  • Higher values indicate better cache effectiveness
  • Low hit rates may indicate cache size needs adjustment

Cache Sizing:

  • Size should not exceed Capacity
  • Monitor the Size/Capacity ratio
  • Adjust capacity in cassandra.yaml if needed

Version Compatibility:

  • Note states "Only Cassandra and DSE prior to version 6.0" for some metrics
  • Cache metrics may vary in newer versions

Performance Impact:

  • KeyCache has minimal overhead and high benefit
  • RowCache can consume significant memory
  • Monitor request rates to understand cache load

Units:

  • Size and Capacity: bytes (with SI units disabled)
  • Hit Rate: percentunit (0.0-1.0 scale)
  • Requests: operations per second (ops)