Function BufFileEndCompression

src/backend/storage/file/buffile.c:1372–1420

* End compression stage. Rewind and prepare the BufFile for decompression. */

 * End compression stage. Rewind and prepare the BufFile for decompression.
 */
static void
BufFileEndCompression(BufFile *file)
{
	ZSTD_outBuffer output;
	size_t		ret;
	int			wrote;
	off_t		pos = 0;

	Assert(file->state == BFS_COMPRESSED_WRITING);

	do {
		output.dst = compression_buffer;
		output.size = BLCKSZ;
		output.pos = 0;

		ret = ZSTD_endStream(file->zstd_context->cctx, &output);
		if (ZSTD_isError(ret))
			elog(ERROR, "%s", ZSTD_getErrorName(ret));

		wrote = FileWrite(file->files[0], output.dst, output.pos, file->curOffset + file->pos + pos, WAIT_EVENT_BUFFILE_WRITE);
		if (wrote != output.pos)
			elog(ERROR, "could not write %d bytes to compressed temporary file: %m", (int) output.pos);
		pos += wrote;
	} while (ret > 0);

	ZSTD_freeCCtx(file->zstd_context->cctx);
	file->zstd_context->cctx = NULL;

	elog(DEBUG1, "BufFile compressed from %ld to %ld bytes",
		 file->uncompressed_bytes, BufFileSize(file));

	/* Done writing. Initialize for reading */
	file->zstd_context->dctx = ZSTD_createDStream();
	if (!file->zstd_context->dctx)
		elog(ERROR, "out of memory");
	ret = ZSTD_initDStream(file->zstd_context->dctx);
	if (ZSTD_isError(ret))
		elog(ERROR, "failed to initialize zstd dstream: %s", ZSTD_getErrorName(ret));

	file->compressed_buffer.src = palloc(BLCKSZ);
	file->compressed_buffer.size = 0;
	file->compressed_buffer.pos = 0;
	file->state = BFS_RANDOM_ACCESS;

	if (BufFileSeek(file, 0, 0, SEEK_SET) != 0)
		elog(ERROR, "could not seek in temporary file: %m");

	file->state = BFS_COMPRESSED_READING;
}

static int
BufFileLoadCompressedBuffer(BufFile *file, void *buffer, size_t bufsize)