Re: Row migrated in new data blocks

xhoster_at_gmail.com schreef:

> "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
>

Xho, as I understand it, oracle just ignores them, as the referenced block will be read eventually. Received on Fri Aug 18 2006 - 07:28:23 CDT