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  1. WiredTiger
  2. WT-4000

Avoid getting two snapshots when setting a read_timestamp

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    Details

    • Type: Improvement
    • Status: Closed
    • Priority: Major - P3
    • Resolution: Fixed
    • Affects Version/s: None
    • Fix Version/s: 3.6.6, 4.0.0-rc0, WT3.1.0
    • Component/s: None
    • Labels:
      None
    • Story Points:
      5
    • Sprint:
      Storage Non-NYC 2018-05-07, Storage Non-NYC 2018-05-21

      Description

      In WT-3981 we get a new transaction snapshot when setting a read_timestamp in a running transaction.

      That means this pattern:

      session->begin_transaction("isolation=snapshot")
      session->timestamp_transaction("read_timestamp=X")
      

      calls __wt_txn_get_snapshot twice.

      Find a way to avoid one of the calls (while making sure that the snapshot is current as of the timestamp_transaction call for correctness). Setting a read timestamp is a relatively common case, and getting the snapshot can be expensive when many sessions are active.

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              Assignee:
              vamsi.krishna Vamsi Boyapati
              Reporter:
              michael.cahill Michael Cahill
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                Created:
                Updated:
                Resolved: