Cache Analysis and Tuning

Analyze ClickHouse cache systems: mark cache, uncompressed cache, query cache, and compiled expression cache.

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Diagnostics

Run all queries from the file checks.sql and analyze the results.

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Cache Sizing Recommendations

Cache	Typical Size	Notes
Mark Cache	5-10% of RAM	Higher if random access patterns
Uncompressed	0 (disabled) or 5-10%	Enable only for specific workloads
Query Cache	1-5GB	For repeated identical queries
Compiled Expression	128MB-1GB	Higher for complex expressions

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Problem Investigation

Poor Mark Cache Hit Ratio

Possible causes:

1. Cache too small for working set
2. Queries scan many different tables
3. Many small queries to cold data

Cache Too Large

If mark cache > 15% RAM:

Solutions:

• Reduce index_granularity for tables with excessive marks
• Drop unused tables
• Reduce mark_cache_size setting

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Cross-Module Triggers

Finding	Load Module	Reason
Cache using too much RAM	altinity-expert-clickhouse-memory	Overall memory analysis
Poor hit ratio + high disk IO	altinity-expert-clickhouse-storage	Disk bottleneck
Many marks per table	altinity-expert-clickhouse-schema	Consider index_granularity tuning
Query cache misses	altinity-expert-clickhouse-reporting	Query pattern analysis

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Settings Reference

Setting	Scope	Notes
mark_cache_size	Server	Global mark cache limit
uncompressed_cache_size	Server	Set to 0 to disable
use_uncompressed_cache	Query	Enable per-query
query_cache_max_size	Server	Query result cache
use_query_cache	Query	Enable per-query