Report correct "n" when retryable update/delete by _id (no shard key) affects multiple docs

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    • Type: Bug
    • Resolution: Unresolved
    • Priority: Major - P3
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    • Affects Version/s: None
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    • Query Execution
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      // Ensure the client is using a session with retryable writes enabled

use test

db.coll.createIndex({a: "hashed"});

db.adminCommand(
  {shardCollection: "test.coll", key: {a: "hashed"}, numInitialChunks: 8})

db.coll.insert({_id: 10, a: 1, b: 1}, {_id: 10, a: 11, b: 1});

db.coll.updateOne({_id: 10}, {$set: {b: 0}})
{
   acknowledged: true,
   insertedId: null,
   matchedCount: 1,
   modifiedCount: 1,
   upsertedCount: 0
}

db.coll.find()
{_id: 10, a: 11, b: 0}
{_id: 10, a: 1, b: 0}
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      // Ensure the client is using a session with retryable writes enabled use test db.coll.createIndex({a: "hashed" }); db.adminCommand( {shardCollection: "test.coll" , key: {a: "hashed" }, numInitialChunks: 8}) db.coll.insert({_id: 10, a: 1, b: 1}, {_id: 10, a: 11, b: 1}); db.coll.updateOne({_id: 10}, {$set: {b: 0}}) { acknowledged: true ,   insertedId: null ,   matchedCount: 1,   modifiedCount: 1,   upsertedCount: 0 } db.coll.find() {_id: 10, a: 11, b: 0} {_id: 10, a: 1, b: 0}
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      On v8.0, when a sharded collection that has an _id value that is present on multiple shards, a retryable multi:false update or delete that targets this _id value (without a shard key) will end up affecting more than one document (due to how retryable updates/deletes by _id without shard key are implemented in v8.0).

      Accepting that behavior for now, a user has reported that they noticed a case where an update by _id (without a shard key) was modifying two documents but was return "n=1". See the "Steps to Reproduce" section for an example.

      The goal of this ticket is to ensure that this bug is fixed in v9.0, and also to explore whether a fix should be backported to v8.0 and v8.2 as well.

            Assignee:
            Unassigned
            Reporter:
            Drew Paroski
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              Created:
              Updated: