Function load_relcache_init_file

src/backend/utils/cache/relcache.c:6123–6543

* load_relcache_init_file -- attempt to load cache from the shared * or local cache init file * * If successful, return true and set criticalRelcachesBuilt or * criticalSharedRelcachesBuilt to true. * If not successful, return false. * * NOTE: we assume we are already switched into CacheMemoryContext. */

 * NOTE: we assume we are already switched into CacheMemoryContext.
 */
static bool
load_relcache_init_file(bool shared)
{
	FILE	   *fp;
	char		initfilename[MAXPGPATH];
	Relation   *rels;
	int			relno,
				num_rels,
				max_rels,
				nailed_rels,
				nailed_indexes,
				magic;
	int			i;

	if (shared)
		snprintf(initfilename, sizeof(initfilename), "global/%s",
				 RELCACHE_INIT_FILENAME);
	else
		snprintf(initfilename, sizeof(initfilename), "%s/%s",
				 DatabasePath, RELCACHE_INIT_FILENAME);

	fp = AllocateFile(initfilename, PG_BINARY_R);
	if (fp == NULL)
		return false;

	/*
	 * Read the index relcache entries from the file.  Note we will not enter
	 * any of them into the cache if the read fails partway through; this
	 * helps to guard against broken init files.
	 */
	max_rels = 100;
	rels = (Relation *) palloc(max_rels * sizeof(Relation));
	num_rels = 0;
	nailed_rels = nailed_indexes = 0;

	/* check for correct magic number (compatible version) */
	if (fread(&magic, 1, sizeof(magic), fp) != sizeof(magic))
		goto read_failed;
	if (magic != RELCACHE_INIT_FILEMAGIC)
		goto read_failed;

	for (relno = 0;; relno++)
	{
		Size		len;
		size_t		nread;
		Relation	rel;
		Form_pg_class relform;
		bool		has_not_null;

		/* first read the relation descriptor length */
		nread = fread(&len, 1, sizeof(len), fp);
		if (nread != sizeof(len))
		{
			if (nread == 0)
				break;			/* end of file */
			goto read_failed;
		}