Re: Estimating HCC ratios

Hi,

as Andi answered already, for uncompressed data you can use DBMS_COMPRESSION.GET_COMPRESSION_RATIO to get a ratio how the compression could be.
Be careful as this real (possible) compression depends on the way data is processed.

If you want to know the compression rate of an already HCC compressed block (or better, Compression Unit) the only method I know is to uncompress the object.
It's even more tricky, as in case you change compression attribute for an already HCC compressed table, the HCC compressed blocks on disk are still there, but you will only find them on non-Exadata system at access ( ORA-64307: hybrid columnar compression is only supported in tablespaces residing on Exadata storage). I don't know of any data dictionary information to show "objects with currently HCC compressed blocks", and also no view with "current compression ratio of object with currently HCC compressed blocks".

best regards,
 Martin

2017-06-28 1:50 GMT+02:00 Pantheon Systems <pantheon.oracle_at_gmail.com>:

> Folks
>
> Is there a way to estimate HCC compression ratios?
>
> I.e.. To what extent HCC is employed in the database ?
>
> Or what percentage of tables are HCC compressed & their ratios & whether
> it is archive high / low and so on (
>
> I'm seeing a lot of information out there by various Oracle partners & ACE
> / OakTable members but nothing that solves this question ?
>
> Thanks
>
>
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>
>
>

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