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  1. WiredTiger
  2. WT-3381

Improve concurrency in the transaction subsystem

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Details

    • Improvement
    • Status: Closed
    • Major - P3
    • Resolution: Fixed
    • None
    • 3.5.11, WT3.0.0
    • None
    • None

    Description

      There is currently a single rwlock protecting reads and writes of data in WT_TXN_GLOBAL. Some of those operations, such as updating the oldest transaction (and timestamp), involve scans that are O(#open sessions).

      Performance should be better with more granular locking, where transactions put themselves on a number of lists (one by transaction ID, one by pinned ID, one by read timestamp, and another by commit timestamp). Each of those lists can be protected by a rwlock, and transactions would only appear in a list when they have the associated ID / timestamp.

      This should make update_oldest into an O(1) operation, and make get_snapshot O(#running transactions) rather than O(#open sessions).

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              michael.cahill@mongodb.com Michael Cahill
              michael.cahill@mongodb.com Michael Cahill
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                Created:
                Updated:
                Resolved: