Function MergeWorkerResults

pg_documentdb/src/aggregation/index_stats.c:339–439

* This takes the output from each worker and creates an aggregated view * which dumps one row per index in the wire compatible format */

 * which dumps one row per index in the wire compatible format
 */
static void
MergeWorkerResults(MongoCollection *collection, List *workerResults,
				   Tuplestorestate *tupleStore, TupleDesc tupleDescriptor)
{
	List *indexDocs = ParseWorkerResults(workerResults);

	bool excludeIdIndex = false;

	/* Since index_stats can be executed in a $lookup/$unionWith
	 * It can run on a worker querying the coordinator - we would need
	 * nested distributed execution.
	 */
	bool enableNestedDistribution = true;
	List *indexes = CollectionIdGetIndexes(collection->collectionId, excludeIdIndex,
										   enableNestedDistribution);

	HTAB *bsonElementHash = CreatePgbsonElementHashSet();

	/* First run through the worker index docs -
	 * For each doc, add the { "indexName": (int64)indexAccesses }
	 * into the bsonElement hash. If the entry for that indexName
	 * already exists, add to the existing size.
	 */
	ListCell *indexCell;
	foreach(indexCell, indexDocs)
	{
		bson_value_t *value = lfirst(indexCell);
		bson_iter_t indexDocIter;
		BsonValueInitIterator(value, &indexDocIter);

		while (bson_iter_next(&indexDocIter))
		{
			pgbsonelement element = { 0 };
			element.path = bson_iter_key(&indexDocIter);
			element.pathLength = bson_iter_key_len(&indexDocIter);
			element.bsonValue = *bson_iter_value(&indexDocIter);

			bool found = false;
			pgbsonelement *foundVal = hash_search(bsonElementHash, &element, HASH_ENTER,
												  &found);
			if (found)
			{
				bool overflowedIgnore = false;
				AddNumberToBsonValue(&foundVal->bsonValue, &element.bsonValue,
									 &overflowedIgnore);
			}
		}
	}

	/* Extract postmaster start time */
	TimestampTz timestamp = PgStartTime;

	bson_value_t startTimeValue = { 0 };
	startTimeValue.value_type = BSON_TYPE_DATE_TIME;
	startTimeValue.value.v_datetime = GetDateTimeFromTimestamp(timestamp);

	/* Now write one row per index based on the collection indexes */
	ListCell *cell;