Re: Row migrated in new data blocks

From: <xhoster_at_gmail.com>
Date: 17 Aug 2006 17:13:34 GMT
Message-ID: <20060817131342.235$F0@newsreader.com>

"frank.van.bortel_at_gmail.com" <frank.van.bortel_at_gmail.com> wrote:

>

> someone is mixing up row migration and row chaining here.
> The OP decribes migration, as I read it.
> I have never seen performance tests examining this, so,
> be our guest.
> Chaining is when a row doesn't "fit" and thus uses two (or more)
> blocks.
> Migrated rows will not affect full table scans, it will affect indexed
> reads.

Will migrated rows effect full table scans if the rowid for the selected rows are needed for some reason? Does the new location of the row contain a pointer back to the original block it was migrated from, so that the real rowid can be determined solely from the new location? If not, it seems like the only way to get the rowid and the data at the same time is for the FTS to break rank when it encounters a pointer to a migrated row and go get the row data rather than waiting for it run across that data during the normal course of the scan.

Xho

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Received on Thu Aug 17 2006 - 12:13:34 CDT