RE: index full scan over an index fast full scan in an analytic f

But the fact is, the access path is still a valid path if the user needs the data returned ordered on the indexed columns. Index_asc or Index_desc should do the job without extra cost.

Waleed

-----Original Message-----
Sent: Friday, October 24, 2003 9:39 PM
To: Multiple recipients of list ORACLE-L function?

Tanel

Tanel Poder wrote:
> As an addition to Vladimir's response:

I cannot provide you with detailed information -- can only give pointers to the documentation -- otherwise it would look suspicious :)

> Full scan will search from index root block using branch blocks to first
> leaf block. And since all leaf blocks have pointers to next and previous
> leaf block in index, sequentially reading only leaf blocks is sufficient
for
> returning all values in index, in order (keys are ordered inside leaf
blocks
> as well).
>
> FFS will scan from index header block (note that index segment header and
> index root block are different ones) up to segment high water mark using
> multiblock reads and ignoring contents of root, branch, bitmap, extent
map,
> freelist group blocks. Rows are returned as they've read from blocks, thus
> no order can be guaranteed.

"Rows are returned as they've read from blocks, thus no order can be guaranteed."

Not rows, but blocks returned as is in order they being read. Keys (rows) are ordered inside leaf blocks -- as you wrote above. So, inside the blocks the order is consistent but blocks are 'mixed' whilst read.

Things (parameters etc.) are changing, as Cary pointed out, principles are not.

-- 
Vladimir Begun
The statements and opinions expressed here are my own and
do not necessarily represent those of Oracle Corporation.

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