Accept "B" in all memory-unit GUCs, and improve error messages.

Commit 6e7baa3 added support for "B" unit, for specifying config options
in bytes. However, it was only accepted in GUC_UNIT_BYTE settings,
wal_segment_size and track_activity_query_size, and not e.g. in work_mem.
This patch makes it consistent, so that "B" accepted in all the same
contexts where "kB", "MB", and so forth are accepted.

Add "B" to the list of accepted units in the error hint, along with "kB",
"MB", etc.

Add an entry in the conversion table for "TB" to "B" conversion. A terabyte
is out of range for any GUC_UNIT_BYTE option, so you always get an "out of
range" error with that, but without it, you get a confusing error message
that claims that "TB" is not an accepted unit, with a hint that nevertheless
lists "TB" as an accepted unit.

Reviewed-by: Alexander Korotkov, Andres Freund
Discussion: https://www.postgresql.org/message-id/1bfe7f4a-7e22-aa6e-7b37-f4d222ed2d67@iki.fi

Author: hlinnaka

src/backend/utils/misc/guc.c

@@ -705,7 +705,7 @@ typedef struct
 	char		unit[MAX_UNIT_LEN + 1]; /* unit, as a string, like "kB" or
 										 * "min" */
 	int			base_unit;		/* GUC_UNIT_XXX */
-	int			multiplier;		/* If positive, multiply the value with this
+	int64		multiplier;		/* If positive, multiply the value with this
 								 * for unit -> base_unit conversion.  If
 								 * negative, divide (with the absolute value) */
 } unit_conversion;
@@ -718,10 +718,16 @@ typedef struct
 #error XLOG_BLCKSZ must be between 1KB and 1MB
 #endif
 
-static const char *memory_units_hint = gettext_noop("Valid units for this parameter are \"kB\", \"MB\", \"GB\", and \"TB\".");
+static const char *memory_units_hint = gettext_noop("Valid units for this parameter are \"B\", \"kB\", \"MB\", \"GB\", and \"TB\".");
 
 static const unit_conversion memory_unit_conversion_table[] =
 {
+	/*
+	 * TB -> bytes conversion always overflows 32-bit integer, so this always
+	 * produces an error.  Include it nevertheless for completeness, and so
+	 * that you get an "out of range" error, rather than "invalid unit".
+	 */
+	{"TB", GUC_UNIT_BYTE, INT64CONST(1024) * 1024 * 1024 * 1024},
 	{"GB", GUC_UNIT_BYTE, 1024 * 1024 * 1024},
 	{"MB", GUC_UNIT_BYTE, 1024 * 1024},
 	{"kB", GUC_UNIT_BYTE, 1024},
@@ -731,21 +737,25 @@ static const unit_conversion memory_unit_conversion_table[] =
 	{"GB", GUC_UNIT_KB, 1024 * 1024},
 	{"MB", GUC_UNIT_KB, 1024},
 	{"kB", GUC_UNIT_KB, 1},
+	{"B", GUC_UNIT_KB, -1024},
 
 	{"TB", GUC_UNIT_MB, 1024 * 1024},
 	{"GB", GUC_UNIT_MB, 1024},
 	{"MB", GUC_UNIT_MB, 1},
 	{"kB", GUC_UNIT_MB, -1024},
+	{"B", GUC_UNIT_MB, -(1024 * 1024)},
 
 	{"TB", GUC_UNIT_BLOCKS, (1024 * 1024 * 1024) / (BLCKSZ / 1024)},
 	{"GB", GUC_UNIT_BLOCKS, (1024 * 1024) / (BLCKSZ / 1024)},
 	{"MB", GUC_UNIT_BLOCKS, 1024 / (BLCKSZ / 1024)},
 	{"kB", GUC_UNIT_BLOCKS, -(BLCKSZ / 1024)},
+	{"B", GUC_UNIT_BLOCKS, -BLCKSZ},
 
 	{"TB", GUC_UNIT_XBLOCKS, (1024 * 1024 * 1024) / (XLOG_BLCKSZ / 1024)},
 	{"GB", GUC_UNIT_XBLOCKS, (1024 * 1024) / (XLOG_BLCKSZ / 1024)},
 	{"MB", GUC_UNIT_XBLOCKS, 1024 / (XLOG_BLCKSZ / 1024)},
 	{"kB", GUC_UNIT_XBLOCKS, -(XLOG_BLCKSZ / 1024)},
+	{"B", GUC_UNIT_XBLOCKS, -XLOG_BLCKSZ},
 
 	{""}						/* end of table marker */
 };