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  1. Core Server
  2. SERVER-49285

Support getMore on snapshot cursor even after unrelated index is created or dropped

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    • Type: Icon: Improvement Improvement
    • Resolution: Duplicate
    • Priority: Icon: Major - P3 Major - P3
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    • Affects Version/s: None
    • Component/s: Catalog
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    • Storage Execution
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    • 3
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      Creating or dropping an index raises the collection's minimum visible snapshot. This causes a getMore on a snapshot cursor to return a SnapshotUnavailable error response, even if it wouldn't use that index. Longer-running snapshot reads would be more useful if their query plan wasn't impacted by the change to the collection's minimum visible snapshot.

      const rst = new ReplSetTest({nodes: 1});
rst.startSet();
rst.initiate();

const db = rst.getPrimary().getDB("test");
assert.commandWorked(db.mycoll.insert(Array.from({length: 5}, (_, i) => ({_id: i}))));
const cursor = db.mycoll.find().readConcern("snapshot").batchSize(1);

assert.eq({_id: 0}, cursor.next());
assert.eq({_id: 1}, cursor.next());
assert.commandWorked(db.mycoll.createIndex({a: 1}));
// HERE: The getMore command fails with SnapshotUnavailable due to the collection's minimum visible
// snapshot being bumped from creating the {a: 1} index.
assert.eq({_id: 2}, cursor.next());

rst.stopSet();

            Assignee:
            backlog-server-execution [DO NOT USE] Backlog - Storage Execution Team
            Reporter:
            max.hirschhorn@mongodb.com Max Hirschhorn
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              Created:
              Updated:
              Resolved: