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Date: Mon, 30 Apr 2012 15:59:20 -0500
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 <CAEik5nNxPd7NqvJHEnQmHh4oB1fuX3a1cAgSpUCJRaeNtQs1sQ@mail.gmail.com>
Subject: Observation on integer types documentation
From: Dan McGee <dpmcgee@gmail.com>
To: pgsql-docs@postgresql.org
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Hey everyone,

Reading the docs today, I came across this paragraph
(http://www.postgresql.org/docs/devel/static/datatype-numeric.html#DATATYPE=
-INT),
which goes back several major versions:

> The type integer is the common choice, as it offers the best balance betw=
een range, storage size, and performance. The smallint type is generally on=
ly used if disk space is at a premium. The bigint type should only be used =
if the range of the integer type is insufficient, because the latter is def=
initely faster.

A few thoughts on this.
1) the use of the word "latter" isn't totally clear, or at least I had
to re-read it to realize former was 'bigint' and latter was 'integer'.
It might just be the style of writing.
2) I'm less than convinced this note belongs in modern documentation,
and set out to test that theory. My full results are below, but the
summary is this: on a 64-bit system, there seems to be only a minimal
measurable performance difference (< 5%) and very little size
difference. In the case of the indexes, the size difference is zero.
This is not true for a 32-bit system (where it is 39% slower), but the
blanket statement doesn't hold true, which is why I'm writing all this
up.

On a final note, the following paragraph also seems like it has
outlived its useful life:

> On very minimal operating systems the bigint type might not function corr=
ectly, because it relies on compiler support for eight-byte integers. On su=
ch machines, bigint acts the same as integer, but still takes up eight byte=
s of storage. (We are not aware of any modern platform where this is the ca=
se.)

Thanks!
-Dan


Table setup (only difference is type of 'id' column):

Table "public.package_files"
    Column    |          Type          |       Modifiers
--------------+------------------------+------------------------
 id           | integer                | not null
 pkg_id       | integer                | not null
 is_directory | boolean                | not null default false
 directory    | character varying(255) | not null
 filename     | character varying(255) |
Indexes:
    "package_files_pkey" PRIMARY KEY, btree (id)
    "package_files_pkg_id" btree (pkg_id) CLUSTER


Table "public.package_files_int8"
    Column    |          Type          |       Modifiers
--------------+------------------------+------------------------
 id           | bigint                 | not null
 pkg_id       | integer                | not null
 is_directory | boolean                | not null default false
 directory    | character varying(255) | not null
 filename     | character varying(255) |
Indexes:
    "package_files_int8_pkey" PRIMARY KEY, btree (id)
    "package_files_int8_pkg_id" btree (pkg_id) CLUSTER


# select count(*) from package_files;
 2621418
# select count(*) from package_files_int8 ;
 2621418


All runs below were done after issuing a few warm up queries, and both
tables went through a VACUUM/CLUSTER/ANALYZE sequence.

32-bit P4 2.4 GHz (single core). no enabled CPU frequency scaling, 1GB
total ram, shared_buffers 128MB, work_mem 4MB:

             relation             |    size
----------------------------------+------------
 public.package_files_int8        | 239 MB
 public.package_files             | 229 MB
 public.package_files_int8_pkey   | 56 MB
 public.package_files_int8_pkg_id | 45 MB
 public.package_files_pkey        | 45 MB
 public.package_files_pkg_id      | 45 MB

archweb=3D> \timing on
Timing is on.
archweb=3D> \t
Showing only tuples.
archweb=3D> select count(*) from (select * from package_files where
pkg_id in (48024, 48025, 40343) order by id) a;
 119325
Time: 516.558 ms
archweb=3D> select count(*) from (select * from package_files where
pkg_id in (48024, 48025, 40343) order by id) a;
 119325
Time: 519.720 ms
archweb=3D> select count(*) from (select * from package_files where
pkg_id in (48024, 48025, 40343) order by id) a;
 119325
Time: 533.330 ms
archweb=3D> select count(*) from (select * from package_files where
pkg_id in (48024, 48025, 40343) order by id) a;
 119325
Time: 519.095 ms
archweb=3D> select count(*) from (select * from package_files where
pkg_id in (48024, 48025, 40343) order by id) a;
 119325
Time: 520.253 ms

archweb=3D> select count(*) from (select * from package_files_int8 where
pkg_id in (48024, 48025, 40343) order by id) a;
 119325
Time: 731.194 ms
archweb=3D> select count(*) from (select * from package_files_int8 where
pkg_id in (48024, 48025, 40343) order by id) a;
 119325
Time: 730.329 ms
archweb=3D> select count(*) from (select * from package_files_int8 where
pkg_id in (48024, 48025, 40343) order by id) a;
 119325
Time: 724.646 ms
archweb=3D> select count(*) from (select * from package_files_int8 where
pkg_id in (48024, 48025, 40343) order by id) a;
 119325
Time: 710.815 ms
archweb=3D> select count(*) from (select * from package_files_int8 where
pkg_id in (48024, 48025, 40343) order by id) a;
 119325
Time: 724.519 ms


64-bit Core2 Quad 2.66 GHz (four core), CPU freq scaling disabled
(performance governor used), 8GB total ram, shared_buffers 128MB,
work_mem 4MB:

             relation             |    size
----------------------------------+------------
 public.package_files_int8        | 245 MB
 public.package_files             | 234 MB
 public.package_files_int8_pkey   | 56 MB
 public.package_files_pkg_id      | 56 MB
 public.package_files_int8_pkg_id | 56 MB
 public.package_files_pkey        | 56 MB

dmcgee=3D# select count(*) from (select * from package_files where
pkg_id in (48024, 48025, 40343) order by id) a;
 119325
Time: 177.078 ms
dmcgee=3D# select count(*) from (select * from package_files where
pkg_id in (48024, 48025, 40343) order by id) a;
 119325
Time: 176.109 ms
dmcgee=3D# select count(*) from (select * from package_files where
pkg_id in (48024, 48025, 40343) order by id) a;
 119325
Time: 177.478 ms
dmcgee=3D# select count(*) from (select * from package_files where
pkg_id in (48024, 48025, 40343) order by id) a;
 119325
Time: 176.639 ms
dmcgee=3D# select count(*) from (select * from package_files where
pkg_id in (48024, 48025, 40343) order by id) a;
 119325
Time: 176.453 ms

dmcgee=3D# select count(*) from (select * from package_files_int8 where
pkg_id in (48024, 48025, 40343) order by id) a;
 119325
Time: 185.768 ms
dmcgee=3D# select count(*) from (select * from package_files_int8 where
pkg_id in (48024, 48025, 40343) order by id) a;
 119325
Time: 185.159 ms
dmcgee=3D# select count(*) from (select * from package_files_int8 where
pkg_id in (48024, 48025, 40343) order by id) a;
 119325
Time: 184.407 ms
dmcgee=3D# select count(*) from (select * from package_files_int8 where
pkg_id in (48024, 48025, 40343) order by id) a;
 119325
Time: 184.555 ms
dmcgee=3D# select count(*) from (select * from package_files_int8 where
pkg_id in (48024, 48025, 40343) order by id) a;
 119325
Time: 184.290 ms


Overall results:

                       i686                            x86_64
                int4            int8            int4            int8
                516.558         731.194         177.078         185.768
                519.72          730.329         176.109         185.159
                533.33          724.646         177.478         184.407
                519.095         710.815         176.639         184.555
                520.253         724.519         176.453         184.29


Average         521.7912        724.3006        176.7514        184.8358
Stddev          6.6040841681    8.1530512264    0.5359499044    0.619288059
Ratio                   1.3881042839                    1.0457388173