Fix pg_size_pretty() to avoid overflow for inputs close to INT64_MAX.

tglsfdc · tglsfdc · commit 6ba0d8d5ac47 · 2011-04-25T16:22:17.000-04:00
The expression that tried to round the value to the nearest TB could
overflow, leading to bogus output as reported in bug #5993 from Nicola
Cossu.  This isn't likely to ever happen in the intended usage of the
function (if it could, we'd be needing to use a wider datatype instead);
but it's not hard to give the expected output, so let's do so.
diff --git a/src/backend/utils/adt/dbsize.c b/src/backend/utils/adt/dbsize.c
@@ -497,9 +497,15 @@ pg_size_pretty(PG_FUNCTION_ARGS)
 							 (size + mult / 2) / mult);
 				else
 				{
+					/* Here we have to worry about avoiding overflow */
+					int64	val;
+
 					mult *= 1024;
+					val = size / mult;
+					if ((size % mult) >= (mult / 2))
+						val++;
 					snprintf(buf, sizeof(buf), INT64_FORMAT " TB",
-							 (size + mult / 2) / mult);
+							 val);
 				}
 			}
 		}

Original file line number	Diff line number	Diff line change
`@@ -497,9 +497,15 @@ pg_size_pretty(PG_FUNCTION_ARGS)`
`497`	`497`	`(size + mult / 2) / mult);`
`498`	`498`	`else`
`499`	`499`	`{`
	`500`	`+ /* Here we have to worry about avoiding overflow */`
	`501`	`+ int64 val;`
	`502`	`+`
`500`	`503`	`mult *= 1024;`
	`504`	`+ val = size / mult;`
	`505`	`+ if ((size % mult) >= (mult / 2))`
	`506`	`+ val++;`
`501`	`507`	`snprintf(buf, sizeof(buf), INT64_FORMAT " TB",`
`502`		`- (size + mult / 2) / mult);`
	`508`	`+ val);`
`503`	`509`	`}`
`504`	`510`	`}`
`505`	`511`	`}`