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  1. Core Server
  2. SERVER-29123

Why is ParallelBatchWriterMode used when Applying Oplogs

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    • Type: Question
    • Status: Closed
    • Priority: Critical - P2
    • Resolution: Done
    • Affects Version/s: None
    • Fix Version/s: None
    • Component/s: Replication
    • Labels:
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      Description

      In function OpTime SyncTail::multiApply, ParallelBatchWriterMode is used.
      If primary is writing heavily, the latency of reading slaves will be very unstable. In our production environment, it may be 400 to 1000ms,
      I know that ParallelBatchWriterMode is a global resource lock, which will block every read operation on every collections.
      My question is that: why is it necessary to stop reads on collections other than oplog.rs?
      Why can not a lock on local db satisfy the concurrency model?

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