Function cdbCopyGetData

src/backend/cdb/cdbcopy.c:284–401

* gets a chunk of rows of data from a copy command. * returns boolean true if done. Caller should still * empty the leftovers in the outbuf in that case. */

 * empty the leftovers in the outbuf in that case.
 */
bool
cdbCopyGetData(CdbCopy *c, bool copy_cancel, uint64 *rows_processed)
{
	SegmentDatabaseDescriptor *q;
	Gang	   *gp;
	int			nbytes;

	/* clean out buf data */
	resetStringInfo(&c->copy_out_buf);

	gp = getCdbCopyPrimaryGang(c);

	/*
	 * MPP-7712: we used to issue the cancel-requests for each *row* we got
	 * back from each segment -- this is potentially millions of
	 * cancel-requests. Cancel requests consist of an out-of-band connection
	 * to the segment-postmaster, this is *not* a lightweight operation!
	 */
	if (copy_cancel)
	{
		ListCell   *cur;

		/* iterate through all the segments that still have data to give */
		foreach(cur, c->seglist)
		{
			int			source_seg = lfirst_int(cur);

			q = getSegmentDescriptorFromGang(gp, source_seg);

			/* send a query cancel request to that segdb */
			PQrequestCancel(q->conn);
		}
	}

	/*
	 * Collect data rows from the segments that still have rows to give until
	 * chunk minimum size is reached
	 */
	while (c->copy_out_buf.len < COPYOUT_CHUNK_SIZE)
	{
		ListCell   *cur;

		/* iterate through all the segments that still have data to give */
		foreach(cur, c->seglist)
		{
			int			source_seg = lfirst_int(cur);
			char	   *buffer;

			q = getSegmentDescriptorFromGang(gp, source_seg);

			/* get 1 row of COPY data */
			nbytes = PQgetCopyData(q->conn, &buffer, false);

			/*
			 * SUCCESS -- got a row of data
			 */
			if (nbytes > 0 && buffer)
			{