Function CollStatsWorker

pg_documentdb/src/commands/coll_stats.c:663–758

* This is the core logic for coll_stats that executes on * every node in the cluster. */

 * every node in the cluster.
 */
static pgbson *
CollStatsWorker(void *fcinfoPointer)
{
	PG_FUNCTION_ARGS = fcinfoPointer;
	Datum databaseName = PG_GETARG_DATUM(0);
	Datum collectionName = PG_GETARG_DATUM(1);

	double modeArgument = PG_GETARG_FLOAT8(2);


	/* Consider this mode in filtering below - but this requires
	 * the coordinator in a multi-node setup to be on the latest version.
	 */
	CollStatsAggMode mode = CollStatsAggMode_CountAndStorage;

	/* Ensure proper conversion to enum */
	int argAsInt = (int) floor(modeArgument);
	if (argAsInt > CollStatsAggMode_None &&
		argAsInt <= CollStatsAggMode_Max)
	{
		mode = argAsInt;
	}

	MongoCollection *collection =
		GetMongoCollectionByNameDatum(databaseName,
									  collectionName,
									  AccessShareLock);

	if (collection == NULL)
	{
		ereport(ERROR, (errcode(ERRCODE_DOCUMENTDB_INVALIDNAMESPACE),
						errmsg("Collection could not be found")));
	}

	/* First step, get the relevant shards on this node (We're already in the query worker) */
	ArrayType *shardNames = NULL;
	ArrayType *shardOids = NULL;

	/* Next get the relation and table size */
	pgbson_writer writer;
	PgbsonWriterInit(&writer);

	/* Only do work if there are shards */
	if (GetMongoCollectionShardOidsAndNames(collection, &shardOids, &shardNames))
	{
		Assert(shardNames != NULL);

		/*
		 * Next get statistics details: Fetch document count from statistics
		 * We don't do runtime counts here - instead we do it in the coordinator
		 * if it's needed.
		 */
		bool isSmallCollection = false;
		int64 documentCount = GetPostgresDocumentCountStats(shardOids,
															&isSmallCollection);

		PgbsonWriterAppendInt64(&writer, "total_doc_count", 15, documentCount);