Re: PG8.3->10 migration data differences

On 9/10/18 6:43 AM, Csaba Ragasits wrote:
> I think I found the solution.
>
> When I set this parameter on the pg10 client connection, the pg10 REAL
> value format same as the pg83 value:
>
> SET extra_float_digits = 0;
>
> Interesting, because the default value is 0 in the postgresql.conf:
> #extra_float_digits = 0                 # min -15, max 3
>
> Do you have any ideas how can I format the miliseconds too?

select version();
version
------------------------------------------------------------------------------------
PostgreSQL 10.5 on x86_64-pc-linux-gnu, compiled by gcc (SUSE Linux)
4.8.5, 64-bit

test=# select '09/10/18 07:10:25.100'::timestamp;
timestamp
-----------------------
2018-09-10 07:10:25.1
(1 row)

test=# select '09/10/18 07:10:25.111'::timestamp;
timestamp
-------------------------
2018-09-10 07:10:25.111

Milliseconds will display if they are significant.

If you want to format the output:

test=# select to_char('09/10/18 07:10:25.100'::timestamp, 'MM/DD/YY
HH:MI:SS.MS');
to_char
-----------------------
09/10/18 07:10:25.100
(1 row)

>
> Thx,
> Csaba
>
> 2018-09-10 12:00 GMT+02:00 Peter J. Holzer <hjp-pgsql(at)hjp(dot)at
> <mailto:hjp-pgsql(at)hjp(dot)at>>:
>
> On 2018-09-10 11:57:42 +0300, Achilleas Mantzios wrote:
> > On 10/09/2018 11:22, Csaba Ragasits wrote:
> >     Hello,
> >
> >     We would like to migrate our old databases to new postgres server,
> >     with the simple backup-restore process. The process run fine
> >     without errors but when we're  checking the source and the
> >     migrated datas as field level, we found the following differences:
> [...]
> >
> >     Field type: REAL
> >     pg93: 2.2
> >     pg10: 2.20000005
> >
> >
> > Those have to do with rounding. Precision for real is 6 decimal
> > digits. Your difference is on the 8-th digit.
>
> Nitpick: Precision is 24 binary digits which is *about* 6 decimal
> digits. The number which is actually stored (on both pg93 and pg10) is
> actually 2.2000000476837158203125 (1.00011001100110011001101 * 2^1 in
> binary). Apparently Pg9.3 rounds this to "2.2" on output while Pg10
> prints the more precise (but still not exact) "2.20000005".
>
> (I would argue that the Pg9.3 output is better, since it represents the
> same value in fewer digits, but always printing the minimum number of
> digits necessary is surprisingly difficult.)
>
>         hp
>
> --
>    _  | Peter J. Holzer    | we build much bigger, better disasters now
> |_|_) |                    | because we have much more sophisticated
> | |   | hjp(at)hjp(dot)at <mailto:hjp(at)hjp(dot)at>         | management tools.
> __/   | http://www.hjp.at/ | -- Ross Anderson <https://www.edge.org/>
>
>

--
Adrian Klaver
adrian(dot)klaver(at)aklaver(dot)com