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  1. Core Server
  2. SERVER-47952

If a snapshot read targets one shard, let the shard choose the timestamp

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    • Icon: Task Task
    • Resolution: Won't Fix
    • Icon: Major - P3 Major - P3
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    • Sharding
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    • Repl 2020-06-01, Repl 2020-06-15
    • 25

    Description

      Normally, a snapshot read outside a multi-document transaction will target multiple shards, and mongos selects a timestamp for readConcern.atClusterTime.

      If only a single shard is targeted, snapshot timestamp selection can be deferred to the mongod. Thus, sending readConcern: {level: "snapshot"} is sufficient. Implement this optimization in mongos. Capture the atClusterTime returned by the shard and store it on the cursor (for find/aggregate) and return it to the client.

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            jesse@mongodb.com A. Jesse Jiryu Davis
            jesse@mongodb.com A. Jesse Jiryu Davis
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