WiredTiger Cache & Checkpoint Flush Architecture

WiredTiger's internal in-memory buffer pool and its 60-second periodic checkpoint cycle that flushes modified dirty cache pages to disk storage.

Internal Architecture Breakdown

WiredTiger allocates 50% of (RAM - 1 GB) to its internal data cache. Writes modify in-memory pages and append redo mutations to the journal; dirty pages are reconciled to disk data files on periodic 60-second checkpoints.

If dirty cache exceeds 20% or total cache exceeds 80%, aggressive foreground thread eviction triggers, inducing severe application latency spikes.

Production Inspection Queries

MongoDB

var c = db.serverStatus().wiredTiger.cache;
print('Bytes in cache:', c['bytes currently in the cache'], 'Dirty bytes:', c['tracked dirty bytes in the cache']);

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