Function write_relmap_file

src/backend/utils/cache/relmapper.c:808–957

* Write out a new shared or local map file with the given contents. * * The magic number and CRC are automatically updated in *newmap. On * success, we copy the data to the appropriate permanent static variable. * * If write_wal is true then an appropriate WAL message is emitted. * (It will be false for bootstrap and WAL replay cases.) * * If send_sinval is true then a SI invalidation mes

 * map update could be happening.
 */
static void
write_relmap_file(bool shared, RelMapFile *newmap,
				  bool write_wal, bool send_sinval, bool preserve_files,
				  Oid dbid, Oid tsid, const char *dbpath)
{
	int			fd;
	RelMapFile *realmap;
	char		mapfilename[MAXPGPATH];

	/*
	 * Fill in the overhead fields and update CRC.
	 */
	newmap->magic = RELMAPPER_FILEMAGIC;
	if (newmap->num_mappings < 0 || newmap->num_mappings > MAX_MAPPINGS)
		elog(ERROR, "attempt to write bogus relation mapping");

	INIT_CRC32C(newmap->crc);
	COMP_CRC32C(newmap->crc, (char *) newmap, offsetof(RelMapFile, crc));
	FIN_CRC32C(newmap->crc);

	/*
	 * Open the target file.  We prefer to do this before entering the
	 * critical section, so that an open() failure need not force PANIC.
	 */
	if (shared)
	{
		snprintf(mapfilename, sizeof(mapfilename), "global/%s",
				 RELMAPPER_FILENAME);
		realmap = &shared_map;
	}
	else
	{
		snprintf(mapfilename, sizeof(mapfilename), "%s/%s",
				 dbpath, RELMAPPER_FILENAME);
		realmap = &local_map;
	}

	fd = OpenTransientFile(mapfilename, O_WRONLY | O_CREAT | PG_BINARY);
	if (fd < 0)
		ereport(ERROR,
				(errcode_for_file_access(),
				 errmsg("could not open file \"%s\": %m",
						mapfilename)));

	if (write_wal)
	{
		xl_relmap_update xlrec;
		XLogRecPtr	lsn;

		/* now errors are fatal ... */
		START_CRIT_SECTION();

		xlrec.dbid = dbid;
		xlrec.tsid = tsid;
		xlrec.nbytes = sizeof(RelMapFile);

		XLogBeginInsert();
		XLogRegisterData((char *) (&xlrec), MinSizeOfRelmapUpdate);