Re: Re: HCC in Pillar Storage

From: Tanel Poder <>
Date: Tue, 20 Mar 2012 17:29:27 +0000
Message-ID: <>

Oracle supports HCC on Exadata and from 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 <> wrote:

> 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?
> >>
> >
> --
Received on Tue Mar 20 2012 - 12:29:27 CDT

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