Re: PG8.3->10 migration data differences - Mailing list pgsql-general

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@hjp.at <mailto:hjp-pgsql@hjp.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
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Adrian Klaver
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