Function XLogReadBufferForRedoExtended

src/backend/access/transam/xlogutils.c:331–435

* XLogReadBufferForRedoExtended * Like XLogReadBufferForRedo, but with extra options. * * In RBM_ZERO_* modes, if the page doesn't exist, the relation is extended * with all-zeroes pages up to the referenced block number. In * RBM_ZERO_AND_LOCK and RBM_ZERO_AND_CLEANUP_LOCK modes, the return value * is always BLK_NEEDS_REDO. * * (The RBM_ZERO_AND_CLEANUP_LOCK mode is redundant with the g

 * using LockBufferForCleanup(), instead of a regular exclusive lock.
 */
XLogRedoAction
XLogReadBufferForRedoExtended(XLogReaderState *record,
							  uint8 block_id,
							  ReadBufferMode mode, bool get_cleanup_lock,
							  Buffer *buf)
{
	XLogRecPtr	lsn = record->EndRecPtr;
	RelFileNode rnode;
	ForkNumber	forknum;
	BlockNumber blkno;
	Page		page;
	bool		zeromode;
	bool		willinit;

	if (!XLogRecGetBlockTag(record, block_id, &rnode, &forknum, &blkno))
	{
		/* Caller specified a bogus block_id */
		elog(PANIC, "failed to locate backup block with ID %d", block_id);
	}

	/*
	 * If a WAL redo function calls XLogReadBufferForRedoExtended() for a page that has a full-page
	 * image, it always succeeds. However, if redo process is only concerned about replaying changes
	 * to a singe page, so replaying any changes for other pages is a waste of cycles. We have modified
     * XLogReadBufferForRedoExtended() to return BLK_DONE for all other pages, to avoid the overhead.
	 */
	if (redo_read_buffer_filter && redo_read_buffer_filter(record, block_id))
	{
	    if (mode == RBM_ZERO_AND_LOCK || mode == RBM_ZERO_AND_CLEANUP_LOCK)
	    {
	        *buf = ReadBufferWithoutRelcache(rnode, forknum,
                                             blkno, mode, NULL);
	        return BLK_DONE;
	    }
	    else
	    {
	        *buf = InvalidBuffer;
	        return BLK_DONE;
	    }
	}

	/*
	 * Make sure that if the block is marked with WILL_INIT, the caller is
	 * going to initialize it. And vice versa.
	 */
	zeromode = (mode == RBM_ZERO_AND_LOCK || mode == RBM_ZERO_AND_CLEANUP_LOCK);
	willinit = (record->blocks[block_id].flags & BKPBLOCK_WILL_INIT) != 0;
	if (willinit && !zeromode)
		elog(PANIC, "block with WILL_INIT flag in WAL record must be zeroed by redo routine");
	if (!willinit && zeromode)
		elog(PANIC, "block to be initialized in redo routine must be marked with WILL_INIT flag in the WAL record");

	/* If it has a full-page image and it should be restored, do it. */
	if (XLogRecBlockImageApply(record, block_id))
	{
		Assert(XLogRecHasBlockImage(record, block_id));
		*buf = XLogReadBufferExtended(rnode, forknum, blkno,
									  get_cleanup_lock ? RBM_ZERO_AND_CLEANUP_LOCK : RBM_ZERO_AND_LOCK);