Re: Re: HCC in Pillar Storage
Date: Tue, 20 Mar 2012 18:46:33 +0100
Thanks for the explanation
So if a tablespace has 2 datafiles, one per array, and if a segment located in the tablespace spans in these two datafiles, can this segment have part of data in HCC and others parts not?
On Tue, Mar 20, 2012 at 6:29 PM, Tanel Poder <tanel_at_tanelpoder.com> wrote:
> Oracle supports HCC on Exadata and from 22.214.171.124 onwards on Oracle's (Sum)
> ZFS appliance and Pillar. Obviously on non-Exadata the *de*compression
> always happens at the database layer (on Exadata it depends on a number of
> things). The compression always happens in the database layer on both
> Exadata and non-Exadata.
> The HCC "support" is decided at the tablespace level, but HCC itself is
> enabled at the segment level. So you can have a table residing in
> HCC-capable tablespace, but you decide not to compress it.
> This segment-level approach also means that you can move the oldest
> partitions of a partitioned fact table onto Pillar/ZFS appliance (and keep
> it compressed with HCC if you want) while keeping the newest partitions of
> the same table on Exadata storage. By the way, even with regular NFS
> appliances or iSCSI storage you can keep some partitions of a table off
> Exadata (without HCC) while keeping other partitions on Exadata.
> *Tanel Poder*
> Enkitec Europe
> +372 56 956 181
> Expert Oracle Exadata book:
> On Tue, Mar 20, 2012 at 4:13 PM, Vit Spinka <vit.spinka_at_vitspinka.cz>
> > The HCC is usually done by the storage; if the storage decides not to do
> > so (e.g. due to CPU load), it will pass the blocks uncompressed and it's
> > then job of the database to uncompress them. So Oracle does not support
> > HCC on non-Exadata/Pillar, but it could do so, but with performance hit.
> > >> I am wondering because I am not very sure where is HCC done, if it is
> > done
> > >> in the DB how the hcc algorithm applies for some blocks (pillar) and
> > some
> > >> not (EVA), if it works shouldnt be a performance hit?
> > >>
> > >
> > --
> > http://www.freelists.org/webpage/oracle-l