Cap wal_buffers to avoid a server crash when it's set very large.

robertmhaas · robertmhaas · commit b09446ed7eec · 2015-08-04T13:12:03.000-04:00
It must be possible to multiply wal_buffers by XLOG_BLCKSZ without
overflowing int, or calculations in StartupXLOG will go badly wrong
and crash the server.  Avoid that by imposing a maximum value on
wal_buffers.  This will be just under 2GB, assuming the usual value
for XLOG_BLCKSZ.

Josh Berkus, per an analysis by Andrew Gierth.
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
@@ -1722,7 +1722,7 @@ static struct config_int ConfigureNamesInt[] =
 			GUC_UNIT_XBLOCKS
 		},
 		&XLOGbuffers,
-		8, 4, INT_MAX, NULL, NULL
+		8, 4, (INT_MAX / XLOG_BLCKSZ), NULL, NULL
 	},
 
 	{

Original file line number	Diff line number	Diff line change
`@@ -1722,7 +1722,7 @@ static struct config_int ConfigureNamesInt[] =`
`1722`	`1722`	`GUC_UNIT_XBLOCKS`
`1723`	`1723`	`},`
`1724`	`1724`	`&XLOGbuffers,`
`1725`		`- 8, 4, INT_MAX, NULL, NULL`
	`1725`	`+ 8, 4, (INT_MAX / XLOG_BLCKSZ), NULL, NULL`
`1726`	`1726`	`},`
`1727`	`1727`
`1728`	`1728`	`{`