Answer
The oplog is a capped collection storing recent operations. Secondaries replay oplog entries to stay in sync.
Quick Answer
The oplog (operations log) is a capped collection on each replica set member that records all write operations. Secondaries continuously tail the primary's oplog and apply operations in order. Replication lag grows when secondaries can't keep up. Change streams use the oplog. Oplog size matters: if a secondary falls too far behind, the oplog might not contain the missing entries.
S
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