Re: PG8.3->10 migration data differences

Hello,

We would like to migrate from 8.3 to 10 version. We've hundreds databases
with different structures. That reason we're working on an automatic data
comparing process.

I've found the following storage settings:
- pg83: Date/time type storage: 64-bit integers
- pg10: Date/time type storage: 64-bit integers

When I running the following select from psql (Select '09/10/18
07:10:25.110'::timestamp;)
The results are same:
-pg83: 2018-09-10 07:10:25.11
-pg10: 2018-09-10 07:10:25.11

When I select it from a table (Select v.entry_timestamp from t_vis v):
The results are different:
- pg83: 2015-08-28 21:25:07.70
- pg10: 2015-08-28 21:25:07.7

The field type:
entry_timestamp TIMESTAMP WITHOUT TIME ZONE NOT NULL,

Our difference every time the last 0 values. The time values are same, but
our field based data comparing mechanism every time mark it as error.

thx,
Csaba

2018-09-10 16:21 GMT+02:00 Adrian Klaver <adrian(dot)klaver(at)aklaver(dot)com>:

> 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
>