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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