Re: When does CLUSTER occur?

The data files contain only one active version of every record. Different
versions of that same record are maintained in a version store.

Kind regards/met vriendelijke groet,

Serge Fonville

http://www.sergefonville.nl

Convince Microsoft!
They need to add TRUNCATE PARTITION in SQL Server
https://connect.microsoft.com/SQLServer/feedback/details/417926/truncate-partition-of-partitioned-table

2012/11/29 Igor Neyman <ineyman(at)perceptron(dot)com>

>
> From: Mike Christensen [mailto:mike(at)kitchenpc(dot)com]
> Sent: Thursday, November 29, 2012 1:35 PM
> To: sthomas(at)optionshouse(dot)com
> Cc: Jeff Janes; Schnabel, Robert D.; pgsql-general(at)postgresql(dot)org
> Subject: Re: When does CLUSTER occur?
>
>
> On Thu, Nov 29, 2012 at 10:28 AM, Shaun Thomas <sthomas(at)optionshouse(dot)com>
> wrote:
> On 11/29/2012 12:20 PM, Jeff Janes wrote:
> It would maintain an imperfect clustering, but still much better than
> current behavior.
>
> I thought about that, too. The "imperfect clustering" made me erase
> everything I'd written. If the clustering is imperfect, it's not really
> clustering. It would mean less random reads to restart the seek chain
> though, so it would be a perceptible gain. But it's still not real
> clustering until the order is maintained indefinitely.
>
> So far as I know, that simply can't be done with MVCC. Especially on an
> insert-only table that's clustered on a column unrelated to insert order.
>
>
> How is this implemented in MS SQL then? Obviously, MS SQL supports real
> clustering and has MVCC..
>
> --
>
> The way MVCC implemented in Postgres (not allowing "in place" updates) is
> obviously complicates things in regards to clustering.
>
> As for MS SQL, here is how it implements clustering:
> The index on which the table is clustered actually becomes a "physical
> holder" (for the lack of better term) of the table, meaning the complete
> table tuples are stored in the leaf blocks of the index it is clustered on.
> There is no other place in the database where they are stored physically.
>
> Regards,
> Igor Neyman
>
>
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