Function ReadBufferExtended

src/backend/storage/buffer/bufmgr.c:827–857

* ReadBufferExtended -- returns a buffer containing the requested * block of the requested relation. If the blknum * requested is P_NEW, extend the relation file and * allocate a new block. (Caller is responsible for * ensuring that only one backend tries to extend a * relation at the same time!) * * Returns: the buffer number for the buffer containing * the block read. The return

 * See buffer/README for details.
 */
Buffer
ReadBufferExtended(Relation reln, ForkNumber forkNum, BlockNumber blockNum,
				   ReadBufferMode mode, BufferAccessStrategy strategy)
{
	bool		hit;
	Buffer		buf;

	/* Open it at the smgr level if not already done */
	RelationOpenSmgr(reln);

	/*
	 * Reject attempts to read non-local temporary relations; we would be
	 * likely to get wrong data since we have no visibility into the owning
	 * session's local buffers.
	 */
	if (RelationUsesLocalBuffers(reln) && RELATION_IS_OTHER_TEMP(reln))
		ereport(ERROR,
				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
				 errmsg("cannot access temporary tables of other sessions")));

	/*
	 * Read the buffer, and update pgstat counters to reflect a cache hit or
	 * miss.
	 */
	pgstat_count_buffer_read(reln);
	buf = ReadBuffer_common(reln->rd_smgr, reln->rd_rel->relpersistence,
							forkNum, blockNum, mode, strategy, &hit);
	if (hit)
		pgstat_count_buffer_hit(reln);
	return buf;
}


/*