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/**
* Loading this file overrides DB.prototype.getCollection() with a function that attempts to shard
* the collection before returning it.
*
* The DB.prototype.getCollection() function is called whenever an undefined property is accessed
* on the db object.
*
* DBCollection.prototype.drop() function will re-shard any non-blacklisted collection that is
* dropped in a sharded cluster.
*/
(function() {
'use strict';
// Save a reference to the original getCollection method in the IIFE's scope.
// This scoping allows the original method to be called by the getCollection override below.
var originalGetCollection = DB.prototype.getCollection;
var originalDBCollectionDrop = DBCollection.prototype.drop;
// Blacklisted namespaces that should not be sharded.
var blacklistedNamespaces = [
/\$cmd/,
/^admin\./,
/^config\./,
/\.system\./,
];
function shardCollection(collection) {
var db = collection.getDB();
var dbName = db.getName();
var fullName = collection.getFullName();
for (var ns of blacklistedNamespaces) {
if (fullName.match(ns)) {
return;
}
}
var res = db.adminCommand({enableSharding: dbName});
// enableSharding may only be called once for a database.
if (res.code !== ErrorCodes.AlreadyInitialized) {
assert.commandWorked(res, "enabling sharding on the '" + dbName + "' db failed");
}
res = db.adminCommand({shardCollection: fullName, key: {_id: 'hashed'}});
assert.commandWorked(res, "sharding '" + fullName + "' with a hashed _id key failed");
}
DB.prototype.getCollection = function() {
var collection = originalGetCollection.apply(this, arguments);
// If the collection exists, there must have been a previous call to getCollection
// where we sharded the collection so there's no need to do it again.
if (collection.exists()) {
return collection;
}
// Attempt to enable sharding on database and collection if not already done.
shardCollection(collection);
return collection;
};
DBCollection.prototype.drop = function() {
var dropResult = originalDBCollectionDrop.apply(this, arguments);
// Attempt to enable sharding on database and collection if not already done.
shardCollection(this);
return dropResult;
};
}());
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