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  1. Core Server
  2. SERVER-92806

Plan cache entry ignores index collation with $elemMatch

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    • Query Optimization
    • Fully Compatible
    • ALL
    • v8.0, v7.0, v6.0, v5.0
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      const conn = MongoRunner.runMongod();
const db = conn.getDB(jsTestName());

const documentList = [
    {_id: 47, "obj": {"array": ["lowercase"]}},
    {_id: 78, "obj": {"array": ["lowercase"]}},
];

let coll = db.bf34252;
coll.drop();
assert.commandWorked(coll.insert(documentList));

// Create two indexes and run the query twice to create an _active_ plan cache entry.
assert.commandWorked(coll.createIndex({"obj.array": 1}, {
    collation: {locale: 'en'},
}));
assert.commandWorked(coll.createIndex({"obj.array": 1, unused: 1}, {
    collation: {locale: 'en'},
}));

// Sanity check
const match2 = {"obj.array": {$elemMatch: {$gte: "UPPERCASE"}}};
assert.eq(2, coll.find(match2).itcount());

for (let i = 0; i < 2; ++i) {
    coll.find({"obj.array": {$elemMatch: {$gte: NumberLong("78219")}}}).itcount();
}

assert.eq(2, coll.find(match2).itcount()); // <---- THIS ASSERTION FAILS

MongoRunner.stopMongod(conn);
      Show
      const conn = MongoRunner.runMongod(); const db = conn.getDB(jsTestName()); const documentList = [ {_id: 47, "obj" : { "array" : [ "lowercase" ]}}, {_id: 78, "obj" : { "array" : [ "lowercase" ]}}, ]; let coll = db.bf34252; coll.drop(); assert.commandWorked(coll.insert(documentList)); // Create two indexes and run the query twice to create an _active_ plan cache entry. assert.commandWorked(coll.createIndex({ "obj.array" : 1}, { collation: {locale: 'en' }, })); assert.commandWorked(coll.createIndex({ "obj.array" : 1, unused: 1}, { collation: {locale: 'en' }, })); // Sanity check const match2 = { "obj.array" : {$elemMatch: {$gte: "UPPERCASE" }}}; assert.eq(2, coll.find(match2).itcount()); for (let i = 0; i < 2; ++i) { coll.find({ "obj.array" : {$elemMatch: {$gte: NumberLong( "78219" )}}}).itcount(); } assert.eq(2, coll.find(match2).itcount()); // <---- THIS ASSERTION FAILS MongoRunner.stopMongod(conn);
    • QO 2024-08-05
    • 200
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      The plan cache key should distinguish between two queries with predicates which differ in index compatibility due to index collation. This does not happen when $elemMatch is present in the predicate.

            Assignee:
            hana.pearlman@mongodb.com Hana Pearlman
            Reporter:
            jess.balint@mongodb.com Jess Balint
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              Created:
              Updated:
              Resolved:
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