Oppolzer - Informatik / Blog

AFAIK, there is a stand-alone utility DSN1COMP that tells you about the
compressed size vs. original size ...

but I don't have practical experience with this.

Kind regards

Bernd



Am 09.03.2015 um 16:20 schrieb Bernd Oppolzer:
> I forgot about that:
>
> from DB2 SQL Reference:
>
> Column of SYSIBM.SYSTABLES:
>
> PCTROWCOMP
> SMALLINT NOT NULL WITH DEFAULT
>
> Percentage of rows compressed within the total number of active rows in the table.
> This includes any row in a table space that is defined with COMPRESS YES.
> The value is -1 if statistics have not been gathered, or the row describes a view, alias,
> created temporary table, or auxiliary table. This is an updatable column.
>
> Kind regards
>
> Bernd
>
>
> Am 09.03.2015 um 16:14 schrieb Bernd Oppolzer:
>> just a wild guess on the original question:
>>
>> the value 98 % could be the part of the rows that are compressed
>> (that is, that have the "compressed" bit on), because not every row
>> is compressed ... rows are compressed only, if the resulting length
>> is shorter that the original length ... if not (which is possible with
>> dictionary-based compression algorithms), the row is stored in
>> non-compressed format.
>>
>> So the 98 % would tell you nothing about the ratio of compressed size
>> to original size ...
>>
>> but I don't really know that. I guess that this value comes from a
>> SYSTABLES column ... so I would look at the SQL reference manual
>> and check if there is a description.
>>
>> Kind regards
>>
>> Bernd
>>
>>
>>
>> Am 09.03.2015 um 15:56 schrieb J.M.:
>>>
>>> Dear Listers,
>>>
>>> Infocenter is giving me more headache than information...
>>>
>>> I am looking at the "Interpretation of an Object in SYSTABLES" panel in the
>>> DB2 Administration tool. One of the fields is called "% compressed:" and it
>>> shows a value of 98. Now this figure strikes me as odd, because, given the kind
>>> of data that is stored in that table, it seems hard to believe that it would
>>> compress to only 2 percent of the original size. And if I am reading the figure
>>> wrong and need to interpret it inversely, then it is equally difficult to
>>> believe that the compressed data would still require 98 percent of the original
>>> size...
>>>
>>> So, naive as I am, I place the cursor on the field and hit PF1, confident that
>>> contextual help will kick in and tell me... Big dissappointment... The only
>>> thing the help is telling me is that I should look at the DB2 product
>>> documentation at http://publib.boulder.ibm.com/infocenter/imzic This now
>>> redirects to the IBM Knowledge Center main page, which is equally crap as the
>>> Infocenter.
>>>
>>> Can anyone please tell me where I can find a simple description of the
>>> different panels and fields shown by the DB2 Administration tool?
>>>
>>> Thanks and very best regards,
>>>
>>> J.
>>>
>>>
>>>
>>> P.S. O, did I mention that Infocenter is crap? PLEASE, IBM, give us back Book Manager.
>>>
>>>
>>>
>