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See Cache: audit and review the caching in Meza #111

The following was AI generated and should be marked as verified after review

Semantic MediaWiki Additional Caching Mechanisms edit

Semantic MediaWiki (SMW) adds several specialized caching layers beyond standard MediaWiki caching.

SMW-Specific Cache Types edit

Query Result Cache edit

Purpose: Caches results of #ask queries and concept queries
Configuration: $smwgQueryResultCacheType and $smwgQueryResultCacheLifetime
Default: Uses MediaWiki's main cache (CACHE_ANYTHING)
Storage: Separate from page cache, stores semantic query results

Property Table Cache edit

Purpose: Caches the mapping of properties to their database tables
Key Variable: $smwgPropertiesCache
Impact: Affects how SMW resolves which table contains property values
Invalidation: Triggered on property type changes or new properties

Concept Cache edit

Purpose: Pre-computed query results for [[Category:Concepts]]
Configuration: $smwgAutoRefreshSubject controls auto-refresh
Mechanism: Runs concept queries in background, stores results
Manual Refresh: php maintenance/SMW_refreshData.php -page "Concept:Name"

Dependency Cache edit

Purpose: Tracks dependencies between pages with semantic data
Function: Ensures pages using #ask queries update when source data changes
Integration: Works with MediaWiki's LinksUpdate system
Performance: Can cause cascading updates on heavily-queried wikis

Statistical Cache edit

Purpose: Caches statistics about semantic data (property usage counts, etc.)
Location: Special:Statistics and Special:Properties pages
Configuration: $smwgStatisticsCache and $smwgStatisticsRefreshInterval

Serializer Cache edit

Purpose: Caches serialized semantic data objects (DIWikiPage, DIProperty)
Type: Object-level caching for frequently accessed semantic entities
Benefit: Reduces database queries for property metadata

Key Differences from Standard MediaWiki Caching edit

Aspect	MediaWiki	Semantic MediaWiki
Parser Cache	Caches rendered HTML	Also stores embedded query metadata
Link Tables	Simple page-to-page links	Complex property-value relationships
Cache Invalidation	On page edit	On edit + when queried data changes
Database Load	Primarily page text	+ semantic property tables (20+ tables)

Configuration in Meza Context edit

In /opt/conf-meza/public/<env>/LocalSettings.php or extension configs:

// Query result caching
$smwgQueryResultCacheType = CACHE_MEMCACHED; // or CACHE_REDIS
$smwgQueryResultCacheLifetime = 3600; // seconds

// Enable query dependency tracking
$smwgEnabledQueryDependencyLinksStore = true;

// Concept cache refresh
$smwgAutoRefreshSubject = true; // Auto-refresh concepts on edit

Performance Implications edit

High-Impact Scenarios edit

Inline Queries: Pages with many {{#ask:}} queries benefit most from query cache
Concepts: Pre-cached concepts avoid expensive runtime queries
Property Pages: Heavily accessed properties (like [[Has type::Page]]) benefit from property cache

Cache Warming Strategies edit

# Rebuild semantic data cache
php maintenance/SMW_refreshData.php -d 50 -v

# Refresh specific namespace
php maintenance/SMW_refreshData.php -page "Property:*" -v

# Force rebuild with full delete
php maintenance/SMW_refreshData.php -d 50 -v -f

Debugging SMW Cache Issues edit

# Check SMW cache status
php maintenance/SMW_debugCaches.php

# Clear SMW query cache
php maintenance/SMW_clearQueryCache.php

# View cache backend
grep smwgQueryResultCacheType /opt/conf-meza/public/<env>/LocalSettings.php

Integration with Meza's Caching edit

Meza's MediaWiki role configures:

Memcached/Redis: Backend for $smwgQueryResultCacheType
Parser Cache: Shared cache for rendered pages with SMW queries
Database Query Cache: MySQL query cache affects property table reads

The mediawiki role in Meza handles SMW cache configuration through templates in src/roles/mediawiki/templates/, particularly in the extension-specific configuration files.

Meza/caching

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