Dictionary Diagnostics

Analyze external dictionaries: configuration, memory usage, reload status, and performance.

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Diagnostics

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

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Dictionary Reload Operations

Force Reload (syntax reference)

-- SYSTEM RELOAD DICTIONARY {database}.{name}
-- SYSTEM RELOAD DICTIONARIES

Check Reload Result for Specific Dictionary

-- Check reload result
select
    name,
    status,
    loading_start_time,
    loading_duration,
    last_exception
from system.dictionaries
where name = '{dictionary_name}'

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Best Practices

Dictionary Sizing Guidelines

Elements	Recommended Type
< 100K	Flat (if sequential keys)
100K - 10M	Hashed
> 10M	Consider partitioning or cache
Complex keys	ComplexKeyHashed
Sparse access	Cache with SSD

Common Issues

Symptom	Cause	Solution
High memory	Too many elements	Use cache type, filter data
Slow reload	Large source table	Add filters, use delta updates
Stale data	Source unreachable	Check connectivity, add retry
Failed status	Source query fails	Check source table/query

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Cross-Module Triggers

Finding	Load Module	Reason
High memory usage	altinity-expert-clickhouse-memory	Overall memory analysis
Load failures	altinity-expert-clickhouse-overview	Error summary + routing
Source connectivity	altinity-expert-clickhouse-logs	Log investigation
Slow lookups	altinity-expert-clickhouse-reporting	Query optimization

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Settings Reference

Setting	Notes
dictionaries_lazy_load	Load on first access vs startup
dictionary_load_wait_timeout_ms	Wait time for lazy load
max_dictionary_num_to_warn	Warning threshold