*** a/src/backend/access/transam/xlog.c
--- b/src/backend/access/transam/xlog.c
***************
*** 105,110 **** int			wal_level = WAL_LEVEL_MINIMAL;
--- 105,111 ----
  int			CommitDelay = 0;	/* precommit delay in microseconds */
  int			CommitSiblings = 5; /* # concurrent xacts needed to sleep */
  int			wal_retrieve_retry_interval = 5000;
+ int			max_slot_wal_keep_size_mb = 0;
  
  #ifdef WAL_DEBUG
  bool		XLOG_DEBUG = false;
***************
*** 9365,9373 **** KeepLogSeg(XLogRecPtr recptr, XLogSegNo *logSegNo)
--- 9366,9397 ----
  	if (max_replication_slots > 0 && keep != InvalidXLogRecPtr)
  	{
  		XLogSegNo	slotSegNo;
+ 		int			slotlimitsegs = ConvertToXSegs(max_slot_wal_keep_size_mb);
  
  		XLByteToSeg(keep, slotSegNo);
  
+ 		/*
+ 		 * ignore slots if too many wal segments are kept.
+ 		 * max_slot_wal_keep_size is just accumulated on wal_keep_segments.
+ 		 */
+ 		if (max_slot_wal_keep_size_mb > 0 && slotSegNo + slotlimitsegs < segno)
+ 		{
+ 			segno = segno - slotlimitsegs; /* must be positive */
+ 
+ 			/*
+ 			 * warn only if the checkpoint flushes the required segment.
+ 			 * we assume here that *logSegNo is calculated keep location.
+ 			 */
+ 			if (slotSegNo < *logSegNo)
+ 				ereport(WARNING,
+ 					(errmsg ("restart LSN of replication slots is ignored by checkpoint"),
+ 					 errdetail("Some replication slots have lost required WAL segnents to continue by up to %ld segments.",
+ 					   (segno < *logSegNo ? segno : *logSegNo) - slotSegNo)));
+ 
+ 			/* emergency vent */
+ 			slotSegNo = segno;
+ 		}
+ 
  		if (slotSegNo <= 0)
  			segno = 1;
  		else if (slotSegNo < segno)
*** a/src/backend/utils/misc/guc.c
--- b/src/backend/utils/misc/guc.c
***************
*** 2371,2376 **** static struct config_int ConfigureNamesInt[] =
--- 2371,2387 ----
  	},
  
  	{
+ 		{"max_slot_wal_keep_size", PGC_SIGHUP, REPLICATION_SENDING,
+ 			gettext_noop("Sets the maximum size of extra WALs kept by replication slots."),
+ 		 NULL,
+ 		 GUC_UNIT_MB
+ 		},
+ 		&max_slot_wal_keep_size_mb,
+ 		0, 0, INT_MAX,
+ 		NULL, NULL, NULL
+ 	},
+ 
+ 	{
  		{"wal_sender_timeout", PGC_SIGHUP, REPLICATION_SENDING,
  			gettext_noop("Sets the maximum time to wait for WAL replication."),
  			NULL,
*** a/src/backend/utils/misc/postgresql.conf.sample
--- b/src/backend/utils/misc/postgresql.conf.sample
***************
*** 235,240 ****
--- 235,241 ----
  #max_wal_senders = 10		# max number of walsender processes
  				# (change requires restart)
  #wal_keep_segments = 0		# in logfile segments, 16MB each; 0 disables
+ #max_slot_wal_keep_size = 0	# measured in bytes; 0 disables
  #wal_sender_timeout = 60s	# in milliseconds; 0 disables
  
  #max_replication_slots = 10	# max number of replication slots
*** a/src/include/access/xlog.h
--- b/src/include/access/xlog.h
***************
*** 97,102 **** extern bool reachedConsistency;
--- 97,103 ----
  extern int	min_wal_size_mb;
  extern int	max_wal_size_mb;
  extern int	wal_keep_segments;
+ extern int	max_slot_wal_keep_size_mb;
  extern int	XLOGbuffers;
  extern int	XLogArchiveTimeout;
  extern int	wal_retrieve_retry_interval;