Answer
The primary writes operations to the oplog; secondaries tail the oplog and apply changes in timestamp order for consistent replication.
Quick Answer
The oplog is a capped collection. Each entry records a write operation (with document data for idempotent replay). Secondaries tail the primary oplog and apply entries. If a secondary falls too far behind (oplog is overwritten before secondary catches up), the secondary goes into RECOVERING state and needs full resync. Size oplog large enough to cover expected lag and maintenance windows.
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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