Answer
The working set is frequently accessed data and indexes. Performance drops if it exceeds available RAM.
Quick Answer
Working set is the data and indexes that MongoDB actively uses - what fits in RAM. When working set fits in WiredTiger's cache (60% of RAM by default), reads are served from memory. When working set exceeds RAM, MongoDB pages data to/from disk - causing I/O spikes and slow reads. Size your RAM so the frequently accessed working set fits. Monitor using serverStatus.wiredTiger.cache metrics.
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SugharaIQ Editorial Team
Verified Answer
This answer has been peer-reviewed by industry experts holding senior engineering roles to ensure technical accuracy and relevance for modern interview standards.
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Source: SugharaIQ