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Commit 6de3a21

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david-rowleydavid-rowley
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Fix incorrect return value in pg_size_pretty(bigint)
Due to how pg_size_pretty(bigint) was implemented, it's possible that when given a negative number of bytes that the returning value would not match the equivalent positive return value when given the equivalent positive number of bytes. This was due to two separate issues. 1. The function used bit shifting to convert the number of bytes into larger units. The rounding performed by bit shifting is not the same as dividing. For example -3 >> 1 = -2, but -3 / 2 = -1. These two operations are only equivalent with positive numbers. 2. The half_rounded() macro rounded towards positive infinity. This meant that negative numbers rounded towards zero and positive numbers rounded away from zero. Here we fix #1 by dividing the values instead of bit shifting. We fix #2 by adjusting the half_rounded macro always to round away from zero. Additionally, adjust the pg_size_pretty(numeric) function to be more explicit that it's using division rather than bit shifting. A casual observer might have believed bit shifting was used due to a static function being named numeric_shift_right. However, that function was calculating the divisor from the number of bits and performed division. Here we make that more clear. This change is just cosmetic and does not affect the return value of the numeric version of the function. Here we also add a set of regression tests both versions of pg_size_pretty() which test the values directly before and after the function switches to the next unit. This bug was introduced in 8a1fab3. Prior to that negative values were always displayed in bytes. Author: Dean Rasheed, David Rowley Discussion: https://postgr.es/m/CAEZATCXnNW4HsmZnxhfezR5FuiGgp+mkY4AzcL5eRGO4fuadWg@mail.gmail.com Backpatch-through: 9.6, where the bug was introduced.
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‎src/backend/utils/adt/dbsize.c

Copy file name to clipboardExpand all lines: src/backend/utils/adt/dbsize.c
+21-16Lines changed: 21 additions & 16 deletions
Original file line numberDiff line numberDiff line change
@@ -31,8 +31,8 @@
3131
#include "utils/relmapper.h"
3232
#include "utils/syscache.h"
3333

34-
/* Divide by two and round towards positive infinity. */
35-
#define half_rounded(x) (((x) + ((x) < 0 ? 0 : 1)) / 2)
34+
/* Divide by two and round away from zero */
35+
#define half_rounded(x) (((x) + ((x) < 0 ? -1 : 1)) / 2)
3636

3737
/* Return physical size of directory contents, or 0 if dir doesn't exist */
3838
static int64
@@ -542,25 +542,29 @@ pg_size_pretty(PG_FUNCTION_ARGS)
542542
snprintf(buf, sizeof(buf), INT64_FORMAT " bytes", size);
543543
else
544544
{
545-
size >>= 9; /* keep one extra bit for rounding */
545+
/*
546+
* We use divide instead of bit shifting so that behavior matches for
547+
* both positive and negative size values.
548+
*/
549+
size /= (1 << 9); /* keep one extra bit for rounding */
546550
if (Abs(size) < limit2)
547551
snprintf(buf, sizeof(buf), INT64_FORMAT " kB",
548552
half_rounded(size));
549553
else
550554
{
551-
size >>= 10;
555+
size /= (1 << 10);
552556
if (Abs(size) < limit2)
553557
snprintf(buf, sizeof(buf), INT64_FORMAT " MB",
554558
half_rounded(size));
555559
else
556560
{
557-
size >>= 10;
561+
size /= (1 << 10);
558562
if (Abs(size) < limit2)
559563
snprintf(buf, sizeof(buf), INT64_FORMAT " GB",
560564
half_rounded(size));
561565
else
562566
{
563-
size >>= 10;
567+
size /= (1 << 10);
564568
snprintf(buf, sizeof(buf), INT64_FORMAT " TB",
565569
half_rounded(size));
566570
}
@@ -621,13 +625,13 @@ numeric_half_rounded(Numeric n)
621625
}
622626

623627
static Numeric
624-
numeric_shift_right(Numeric n, unsigned count)
628+
numeric_truncated_divide(Numeric n, int64 divisor)
625629
{
626630
Datum d = NumericGetDatum(n);
627631
Datum divisor_numeric;
628632
Datum result;
629633

630-
divisor_numeric = NumericGetDatum(int64_to_numeric(((int64) 1) << count));
634+
divisor_numeric = NumericGetDatum(int64_to_numeric(divisor));
631635
result = DirectFunctionCall2(numeric_div_trunc, d, divisor_numeric);
632636
return DatumGetNumeric(result);
633637
}
@@ -650,8 +654,8 @@ pg_size_pretty_numeric(PG_FUNCTION_ARGS)
650654
else
651655
{
652656
/* keep one extra bit for rounding */
653-
/* size >>= 9 */
654-
size = numeric_shift_right(size, 9);
657+
/* size /= (1 << 9) */
658+
size = numeric_truncated_divide(size, 1 << 9);
655659

656660
if (numeric_is_less(numeric_absolute(size), limit2))
657661
{
@@ -660,17 +664,18 @@ pg_size_pretty_numeric(PG_FUNCTION_ARGS)
660664
}
661665
else
662666
{
663-
/* size >>= 10 */
664-
size = numeric_shift_right(size, 10);
667+
/* size /= (1 << 10) */
668+
size = numeric_truncated_divide(size, 1 << 10);
669+
665670
if (numeric_is_less(numeric_absolute(size), limit2))
666671
{
667672
size = numeric_half_rounded(size);
668673
result = psprintf("%s MB", numeric_to_cstring(size));
669674
}
670675
else
671676
{
672-
/* size >>= 10 */
673-
size = numeric_shift_right(size, 10);
677+
/* size /= (1 << 10) */
678+
size = numeric_truncated_divide(size, 1 << 10);
674679

675680
if (numeric_is_less(numeric_absolute(size), limit2))
676681
{
@@ -679,8 +684,8 @@ pg_size_pretty_numeric(PG_FUNCTION_ARGS)
679684
}
680685
else
681686
{
682-
/* size >>= 10 */
683-
size = numeric_shift_right(size, 10);
687+
/* size /= (1 << 10) */
688+
size = numeric_truncated_divide(size, 1 << 10);
684689
size = numeric_half_rounded(size);
685690
result = psprintf("%s TB", numeric_to_cstring(size));
686691
}

‎src/test/regress/expected/dbsize.out

Copy file name to clipboardExpand all lines: src/test/regress/expected/dbsize.out
+42Lines changed: 42 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -35,6 +35,48 @@ SELECT size, pg_size_pretty(size), pg_size_pretty(-1 * size) FROM
3535
1000000000000000.5 | 909 TB | -909 TB
3636
(12 rows)
3737

38+
-- test where units change up
39+
SELECT size, pg_size_pretty(size), pg_size_pretty(-1 * size) FROM
40+
(VALUES (10239::bigint), (10240::bigint),
41+
(10485247::bigint), (10485248::bigint),
42+
(10736893951::bigint), (10736893952::bigint),
43+
(10994579406847::bigint), (10994579406848::bigint),
44+
(11258449312612351::bigint), (11258449312612352::bigint)) x(size);
45+
size | pg_size_pretty | pg_size_pretty
46+
-------------------+----------------+----------------
47+
10239 | 10239 bytes | -10239 bytes
48+
10240 | 10 kB | -10 kB
49+
10485247 | 10239 kB | -10239 kB
50+
10485248 | 10 MB | -10 MB
51+
10736893951 | 10239 MB | -10239 MB
52+
10736893952 | 10 GB | -10 GB
53+
10994579406847 | 10239 GB | -10239 GB
54+
10994579406848 | 10 TB | -10 TB
55+
11258449312612351 | 10239 TB | -10239 TB
56+
11258449312612352 | 10240 TB | -10240 TB
57+
(10 rows)
58+
59+
SELECT size, pg_size_pretty(size), pg_size_pretty(-1 * size) FROM
60+
(VALUES (10239::numeric), (10240::numeric),
61+
(10485247::numeric), (10485248::numeric),
62+
(10736893951::numeric), (10736893952::numeric),
63+
(10994579406847::numeric), (10994579406848::numeric),
64+
(11258449312612351::numeric), (11258449312612352::numeric)) x(size);
65+
size | pg_size_pretty | pg_size_pretty
66+
-------------------+----------------+----------------
67+
10239 | 10239 bytes | -10239 bytes
68+
10240 | 10 kB | -10 kB
69+
10485247 | 10239 kB | -10239 kB
70+
10485248 | 10 MB | -10 MB
71+
10736893951 | 10239 MB | -10239 MB
72+
10736893952 | 10 GB | -10 GB
73+
10994579406847 | 10239 GB | -10239 GB
74+
10994579406848 | 10 TB | -10 TB
75+
11258449312612351 | 10239 TB | -10239 TB
76+
11258449312612352 | 10240 TB | -10240 TB
77+
(10 rows)
78+
79+
-- pg_size_bytes() tests
3880
SELECT size, pg_size_bytes(size) FROM
3981
(VALUES ('1'), ('123bytes'), ('1kB'), ('1MB'), (' 1 GB'), ('1.5 GB '),
4082
('1TB'), ('3000 TB'), ('1e6 MB')) x(size);

‎src/test/regress/sql/dbsize.sql

Copy file name to clipboardExpand all lines: src/test/regress/sql/dbsize.sql
+16Lines changed: 16 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -11,6 +11,22 @@ SELECT size, pg_size_pretty(size), pg_size_pretty(-1 * size) FROM
1111
(1000000000.5::numeric), (1000000000000.5::numeric),
1212
(1000000000000000.5::numeric)) x(size);
1313

14+
-- test where units change up
15+
SELECT size, pg_size_pretty(size), pg_size_pretty(-1 * size) FROM
16+
(VALUES (10239::bigint), (10240::bigint),
17+
(10485247::bigint), (10485248::bigint),
18+
(10736893951::bigint), (10736893952::bigint),
19+
(10994579406847::bigint), (10994579406848::bigint),
20+
(11258449312612351::bigint), (11258449312612352::bigint)) x(size);
21+
22+
SELECT size, pg_size_pretty(size), pg_size_pretty(-1 * size) FROM
23+
(VALUES (10239::numeric), (10240::numeric),
24+
(10485247::numeric), (10485248::numeric),
25+
(10736893951::numeric), (10736893952::numeric),
26+
(10994579406847::numeric), (10994579406848::numeric),
27+
(11258449312612351::numeric), (11258449312612352::numeric)) x(size);
28+
29+
-- pg_size_bytes() tests
1430
SELECT size, pg_size_bytes(size) FROM
1531
(VALUES ('1'), ('123bytes'), ('1kB'), ('1MB'), (' 1 GB'), ('1.5 GB '),
1632
('1TB'), ('3000 TB'), ('1e6 MB')) x(size);

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