Documents with fields MaxKey() value may not be moved on a chunk migration

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    • Type: Bug
    • Resolution: Unresolved
    • Priority: Major - P3
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    • Affects Version/s: None
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      import {ShardingTest} from "jstests/libs/shardingtest.js";

let st = new ShardingTest({shards: 3});

const db = st.s.getDB("test");

assert.commandWorked(st.s.adminCommand({enableSharding: db.getName(), primaryShard: st.shard0.shardName}));

// Create a sharded collection with:
//  - shard key pattern: {x:1}
//  - shard key index: {x:1, y:1}
assert.commandWorked(db.adminCommand({shardCollection: "test.coll", key: {x: 1}}));
db.coll.createIndex({x: 1, y: 1});
db.coll.dropIndex({x: 1});

// Create doc {x: MaxKey(), y:10}
db.coll.insertOne({x: MaxKey(), y: 10});
assert.eq(db.coll.find({}).count(), 1);

// Move chunk
assert.commandWorked(
    db.adminCommand({moveRange: "test.coll", min: {x: 0}, max: {x: MaxKey()}, toShard: st.shard1.shardName}),
);

// The document {x: MaxKey(), y:10} has not been moved
// Consequently, we can't fetch it from the mongos
const docs = db.coll.find().toArray();
assert.eq(docs.length, 1);

db.coll.drop();

st.stop();
      Show
      import {ShardingTest} from "jstests/libs/shardingtest.js"; let st = new ShardingTest({shards: 3}); const db = st.s.getDB("test"); assert.commandWorked(st.s.adminCommand({enableSharding: db.getName(), primaryShard: st.shard0.shardName})); // Create a sharded collection with: //  - shard key pattern: {x:1} //  - shard key index: {x:1, y:1} assert.commandWorked(db.adminCommand({shardCollection: "test.coll", key: {x: 1}})); db.coll.createIndex({x: 1, y: 1}); db.coll.dropIndex({x: 1}); // Create doc {x: MaxKey(), y:10} db.coll.insertOne({x: MaxKey(), y: 10}); assert.eq(db.coll.find({}).count(), 1); // Move chunk assert.commandWorked(     db.adminCommand({moveRange: "test.coll", min: {x: 0}, max: {x: MaxKey()}, toShard: st.shard1.shardName}), ); // The document {x: MaxKey(), y:10} has not been moved // Consequently, we can't fetch it from the mongos const docs = db.coll.find().toArray(); assert.eq(docs.length, 1); db.coll.drop(); st.stop();
    • CAR Team 2026-03-30
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      If a chunk migration uses an index that is longer than the shard key pattern, documents with fields MaxKey() value may not be moved.

      For example:

      • Sharded collection with shard key pattern {x:1}
      • It has the document: {x: MaxKey(), y: 10}
      • A chunk migration uses index {x: 1, y: 1}
      • The chunk migration with a range where max is {x: MaxKey()} will miss that document.

      The upper bound of the range is extended to include all index fields, resulting in {x: MaxKey(), y: MinKey()}. The field y is set to MinKey() because the upper bound is non-inclusive.

            Assignee:
            Unassigned
            Reporter:
            Silvia Surroca
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              Created:
              Updated: