Function GetPrivateRefCountEntry

src/backend/storage/buffer/bufmgr.c:322–395

* Return the PrivateRefCount entry for the passed buffer. * * Returns NULL if a buffer doesn't have a refcount entry. Otherwise, if * do_move is true, and the entry resides in the hashtable the entry is * optimized for frequent access by moving it to the array. */

 * optimized for frequent access by moving it to the array.
 */
static PrivateRefCountEntry *
GetPrivateRefCountEntry(Buffer buffer, bool do_move)
{
	PrivateRefCountEntry *res;
	int			i;

	Assert(BufferIsValid(buffer));
	Assert(!BufferIsLocal(buffer));

	/*
	 * First search for references in the array, that'll be sufficient in the
	 * majority of cases.
	 */
	for (i = 0; i < REFCOUNT_ARRAY_ENTRIES; i++)
	{
		res = &PrivateRefCountArray[i];

		if (res->buffer == buffer)
			return res;
	}

	/*
	 * By here we know that the buffer, if already pinned, isn't residing in
	 * the array.
	 *
	 * Only look up the buffer in the hashtable if we've previously overflowed
	 * into it.
	 */
	if (PrivateRefCountOverflowed == 0)
		return NULL;

	res = hash_search(PrivateRefCountHash,
					  (void *) &buffer,
					  HASH_FIND,
					  NULL);

	if (res == NULL)
		return NULL;
	else if (!do_move)
	{
		/* caller doesn't want us to move the hash entry into the array */
		return res;
	}
	else
	{
		/* move buffer from hashtable into the free array slot */
		bool		found;
		PrivateRefCountEntry *free;

		/* Ensure there's a free array slot */
		ReservePrivateRefCountEntry();

		/* Use up the reserved slot */
		Assert(ReservedRefCountEntry != NULL);
		free = ReservedRefCountEntry;
		ReservedRefCountEntry = NULL;
		Assert(free->buffer == InvalidBuffer);