diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 3c695c1615..da74f00ab2 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -8903,7 +8903,9 @@ can_skip_gucvar(struct config_generic * gconf)
 
 /*
  * estimate_variable_size:
- * Estimate max size for dumping the given GUC variable.
+ *		Compute space needed for dumping the given GUC variable.
+ *
+ * It's OK to overestimate, but not to underestimate.
  */
 static Size
 estimate_variable_size(struct config_generic * gconf)
@@ -8914,9 +8916,8 @@ estimate_variable_size(struct config_generic * gconf)
 	if (can_skip_gucvar(gconf))
 		return 0;
 
-	size = 0;
-
-	size = add_size(size, strlen(gconf->name) + 1);
+	/* Name, plus trailing zero byte. */
+	size = strlen(gconf->name) + 1;
 
 	/* Get the maximum display length of the GUC value. */
 	switch (gconf->vartype)
@@ -8937,7 +8938,7 @@ estimate_variable_size(struct config_generic * gconf)
 				 * small values.  Maximum value is 2147483647, i.e. 10 chars.
 				 * Include one byte for sign.
 				 */
-				if (abs(*conf->variable) < 1000)
+				if (Abs(*conf->variable) < 1000)
 					valsize = 3 + 1;
 				else
 					valsize = 10 + 1;
@@ -8947,11 +8948,12 @@ estimate_variable_size(struct config_generic * gconf)
 		case PGC_REAL:
 			{
 				/*
-				 * We are going to print it with %.17g. Account for sign,
-				 * decimal point, and e+nnn notation. E.g.
-				 * -3.9932904234000002e+110
+				 * We are going to print it with %e with REALTYPE_PRECISION
+				 * fractional digits.  Account for sign, leading digit,
+				 * decimal point, and exponent with up to 3 digits.  E.g.
+				 * -3.99329042340000021e+110
 				 */
-				valsize = REALTYPE_PRECISION + 1 + 1 + 5;
+				valsize = 1 + 1 + 1 + REALTYPE_PRECISION + 5;
 			}
 			break;
 
@@ -8959,7 +8961,15 @@ estimate_variable_size(struct config_generic * gconf)
 			{
 				struct config_string *conf = (struct config_string *) gconf;
 
-				valsize = strlen(*conf->variable);
+				/*
+				 * If the value is NULL, we transmit it as an empty string.
+				 * Although this is not physically the same value, GUC
+				 * generally treats a NULL the same as empty string.
+				 */
+				if (*conf->variable)
+					valsize = strlen(*conf->variable);
+				else
+					valsize = 0;
 			}
 			break;
 
@@ -8972,17 +8982,17 @@ estimate_variable_size(struct config_generic * gconf)
 			break;
 	}
 
-	/* Allow space for terminating zero-byte */
+	/* Allow space for terminating zero-byte for value */
 	size = add_size(size, valsize + 1);
 
 	if (gconf->sourcefile)
 		size = add_size(size, strlen(gconf->sourcefile));
 
-	/* Allow space for terminating zero-byte */
+	/* Allow space for terminating zero-byte for sourcefile */
 	size = add_size(size, 1);
 
-	/* Include line whenever we include file. */
-	if (gconf->sourcefile)
+	/* Include line whenever file is nonempty. */
+	if (gconf->sourcefile && gconf->sourcefile[0])
 		size = add_size(size, sizeof(gconf->sourceline));
 
 	size = add_size(size, sizeof(gconf->source));
@@ -9100,7 +9110,7 @@ serialize_variable(char **destptr, Size *maxbytes,
 			{
 				struct config_real *conf = (struct config_real *) gconf;
 
-				do_serialize(destptr, maxbytes, "%.*g",
+				do_serialize(destptr, maxbytes, "%.*e",
 							 REALTYPE_PRECISION, *conf->variable);
 			}
 			break;
@@ -9109,7 +9119,9 @@ serialize_variable(char **destptr, Size *maxbytes,
 			{
 				struct config_string *conf = (struct config_string *) gconf;
 
-				do_serialize(destptr, maxbytes, "%s", *conf->variable);
+				/* NULL becomes empty string, see estimate_variable_size() */
+				do_serialize(destptr, maxbytes, "%s",
+							 *conf->variable ? *conf->variable : "");
 			}
 			break;
 
@@ -9126,7 +9138,7 @@ serialize_variable(char **destptr, Size *maxbytes,
 	do_serialize(destptr, maxbytes, "%s",
 				 (gconf->sourcefile ? gconf->sourcefile : ""));
 
-	if (gconf->sourcefile)
+	if (gconf->sourcefile && gconf->sourcefile[0])
 		do_serialize_binary(destptr, maxbytes, &gconf->sourceline,
 							sizeof(gconf->sourceline));
 
@@ -9193,7 +9205,7 @@ read_gucstate(char **srcptr, char *srcend)
 	for (ptr = *srcptr; ptr < srcend && *ptr != '\0'; ptr++)
 		;
 
-	if (ptr > srcend)
+	if (ptr >= srcend)
 		elog(ERROR, "could not find null terminator in GUC state");
 
 	/* Set the new position to the byte following the terminating NUL */
@@ -9247,9 +9259,7 @@ RestoreGUCState(void *gucstate)
 	{
 		int			result;
 
-		if ((varname = read_gucstate(&srcptr, srcend)) == NULL)
-			break;
-
+		varname = read_gucstate(&srcptr, srcend);
 		varvalue = read_gucstate(&srcptr, srcend);
 		varsourcefile = read_gucstate(&srcptr, srcend);
 		if (varsourcefile[0])