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  1. Core Server
  2. SERVER-77720

$collStats aggregation with storageStats always results in incrementing docUnitsRead

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    • Type: Icon: Bug Bug
    • Resolution: Duplicate
    • Priority: Icon: Major - P3 Major - P3
    • None
    • Affects Version/s: 7.0.0-rc2
    • Component/s: None
    • None
    • Storage Execution
    • ALL

      When converting from using the legacy collStats command to the $collStats aggregation stage, end-to-end tests have identified that calling the aggregation stage consistently increases docUnitsRead in v7.0 builds of the server. We can reproduce the issue with the following script:

      const node = MongoRunner.runMongod({
  setParameter: { aggregateOperationResourceConsumptionMetrics: true }
});

const admin = node.getDB("admin");
const db = node.getDB("foo");

// add some data to the collection
assert.commandWorked(db.bar.insert({}));

// run test
const first = admin.aggregate([{ $operationMetrics: {} }]).next();
db.bar.aggregate([{ "$collStats": { "storageStats": {} } }]);
const second = admin.aggregate([{ $operationMetrics: {} }]).next();
assert.eq(first.db, second.db);
assert.eq(first.primaryMetrics.docUnitsRead, second.primaryMetrics.docUnitsRead);

MongoRunner.stopMongod(node);

            Assignee:
            backlog-server-execution [DO NOT USE] Backlog - Storage Execution Team
            Reporter:
            matt.broadstone@mongodb.com Matt Broadstone
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              Created:
              Updated:
              Resolved: