Function BufFilePledgeSequential

src/backend/storage/file/buffile.c:1260–1268

* BufFilePledgeSequential * * Promise that the caller will only do sequential I/O on the given file. * This allows the BufFile to be compressed, if 'gp_workfile_compression=on'. * * A sequential file is used in two stages: * * 0. Create file with BufFileCreateTemp(). * 1. Write all data, using BufFileWrite() * 2. Rewind to beginning, with BufFileSeek(file, 0, 0, SEEK_SET). * 3. Read as m

 * that use buffiles across processes pledge sequential access, though.)
 */
void
BufFilePledgeSequential(BufFile *buffile)
{
	if (BufFileSize(buffile) != 0)
		elog(ERROR, "cannot pledge sequential access to a temporary file after writing it");

	if (gp_workfile_compression)
		BufFileStartCompression(buffile);
}

/*
 * The rest of the code is only needed when compression support is compiled in.