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SERVER-84667:index check, avoid create duplicate btree indexes, Avoid affecting performance #1588

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SERVER-84667:index check, avoid create duplicate btree indexes, Avoid affecting performance #1588

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a2a00ec
avoid create_duplicate_btree_indexes
y123456yz Jan 9, 2024
046e439
func name perfect
y123456yz Jan 15, 2024
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36 changes: 34 additions & 2 deletions src/mongo/db/index/index_descriptor.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -247,9 +247,41 @@ IndexDescriptor::Comparison IndexDescriptor::compareIndexOptions(
const IndexCatalogEntry* existingIndex) const {
auto existingIndexDesc = existingIndex->descriptor();

//Index check, avoid creating duplicate indexes.
//For example:
// Add two indexes: db.collection.createIndex({a:1}) and db.collection.createIndex({a:11})
// The two indexes are actually the same, One of them is a useless index
auto canonizeIndexKeyPattern = [this](const BSONObj& indexKeyPattern) {
if (getIndexType() != INDEX_BTREE) {
return indexKeyPattern;
}

//Hidden index is not restricted
if (hidden() == true) {
return indexKeyPattern;
}

BSONObjBuilder build;
BSONObjIterator kpIt(indexKeyPattern);
while (kpIt.more()) {
BSONElement elt = kpIt.next();

// The canonical check as to whether a key pattern element is "ascending" or "descending" is
// (elt.number() >= 0). This is defined by the Ordering class.
invariant(elt.isNumber());
int sortOrder = (elt.number() >= 0) ? 1 : -1;
build.append(elt.fieldName(), sortOrder);
}

return build.obj();
};

BSONObj newIndexKeyPattern = canonizeIndexKeyPattern(keyPattern());
BSONObj existingIndexKeyPattern = canonizeIndexKeyPattern(existingIndexDesc->keyPattern());

// We first check whether the key pattern is identical for both indexes.
if (SimpleBSONObjComparator::kInstance.evaluate(keyPattern() !=
existingIndexDesc->keyPattern())) {
if (SimpleBSONObjComparator::kInstance.evaluate(newIndexKeyPattern !=
existingIndexKeyPattern)) {
return Comparison::kDifferent;
}

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