Answer
Journal files store operations sequentially for atomicity and crash recovery. MongoDB replays journals after restarts.
Quick Answer
Write-ahead logging (WAL / journal): before MongoDB applies any data change, it first writes the operation to the journal file on disk. If the server crashes mid-write, MongoDB replays the journal on startup to complete or roll back the incomplete operation. This ensures the data files are never left in a partially-written, inconsistent state after a crash.
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