Function CopyToDispatchDirectoryTable

src/backend/commands/copyto.c:1800–1884

* Copy FROM directory table TO file, in the dispatcher. Starts a COPY TO command * on each of the executors and gathers all the results and writes it out. */

 * on each of the executors and gathers all the results and writes it out.
 */
static uint64
CopyToDispatchDirectoryTable(CopyToState cstate)
{
	CopyStmt	*stmt = glob_copystmt;
	TupleDesc	tupDesc;
	CdbCopy		*cdbCopy;
	uint64		processed = 0;

	tupDesc = cstate->rel->rd_att;

	cstate->fe_msgbuf = makeStringInfo();
	cdbCopy = makeCdbCopyTo(cstate);

	/*
	 * Start a COPY command in every db of every segment in Apache Cloudberry.
	 *
	 * From this point in the code we need to be extra careful
	 * about error handling. ereport() must not be called until
	 * the COPY command sessions are closed on the executors.
	 * Calling ereport() will leave the executors hanging in
	 * COPY state.
	 */
	elog(DEBUG5, "COPY command sent to segdbs");
	
	PG_TRY();
	{
		bool		done;

		cdbCopyStart(cdbCopy, stmt, cstate->file_encoding);

		if (!cstate->opts.binary)
			ereport(ERROR,
					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
					 errmsg("Only support copy binary to directory table.")));

		/*
		 * This is the main work-loop. In here we keep collecting data from the
		 * COPY commands on the segdbs, until no more data is available. We
		 * keep writing data out a chunk at a time.
		 */
		do
		{
			bool	copy_cancel = (QueryCancelPending ? true : false);

			/* get a chunk of data rows from the QE's */
			done = cdbCopyGetData(cdbCopy, copy_cancel, &processed);

			/* send the chunk of data rows to destination (file or stdout) */
			if (cdbCopy->copy_out_buf.len > 0) /* conditional is important! */
			{
				/*
				 * in the dispatcher we receive chunks of file and flush it.
				 */
				CopySendData(cstate, (void *) cdbCopy->copy_out_buf.data, cdbCopy->copy_out_buf.len);
				CopyToDispatchFlush(cstate);
			}
		} while (!done);