Ian,
I'll look at compressing the index. Does that only work on unique indexes
or can you
do it on non-unique multi-column indexes as well?
Thanks,
Cherie
"MacGregor,
Ian A." To: Multiple recipients of list ORACLE-L
<[EMAIL PROTECTED]>
<[EMAIL PROTECTED] cc:
ford.EDU> Subject: RE: Do fast full index scans do
physical disk reads?
Sent by:
[EMAIL PROTECTED]
om
09/07/01 03:26
PM
Please respond
to ORACLE-L
The advantage of the fast full index scan is that it should read fewer
blocks than the full table scan. Index compression may help reduce the
number of blocks read even further. A unique index mist be at least two
columns wide to benefit from compression.
Ian MacGregor
Stanford Linear Accelerator Center
[EMAIL PROTECTED]
-----Original Message-----
Sent: Friday, September 07, 2001 5:20 AM
To: Multiple recipients of list ORACLE-L
Ian,
The last one I looked at it was cached, I guess. I could purposely cache
the
table (and index) if it was small, though.
I'm confused though. Isn't the whole benefit of the fast, full index scan
that you
don't have to go against the table, thereby avoiding those physical reads?
Or, in the case where the index isn't cached, is the benefit that you don't
have
to read all of the columns in the table that aren't part of the index?
Thanks for your reply,
Cherie
"MacGregor,
Ian A." To: Multiple recipients of
list ORACLE-L <[EMAIL PROTECTED]>
<[EMAIL PROTECTED] cc:
ford.EDU> Subject: RE: Do fast full
index scans do physical disk reads?
Sent by:
[EMAIL PROTECTED]
om
09/07/01 01:05
AM
Please respond
to ORACLE-L
There is no rule that says an index will be cache. Yes physical reads are
being done.
If the unique index is composed of more than one column look into
compressing it.
Ian MacGregor
Stanford Linear Accelerator Center
[EMAIL PROTECTED]
-----Original Message-----
Sent: Thursday, September 06, 2001 1:51 PM
To: Multiple recipients of list ORACLE-L
I am confused by the output from tkprof below. An fast full index
scan is being performed. However, from the statistics, it looks as
thought 649 physical disk reads are being performed. Is that actually
the case? Are physical disk reads being done?
Thanks,
Cherie Machler
Oracle DBA
Gelco Information Network
********************************************************************************
Select SD.KS_OBJECTID as CONCEPTID
>From kbowner.KS_SHORTDESCRIPTION SD
Where SD.KS_DESCRIPTIONTYPE = 'CPTNAME' And
UPPER(SD.KS_DESCRIPTIONTEXT) = ''
call count cpu elapsed disk query current
rows
------- ------ -------- ---------- ---------- ---------- ----------
----------
Parse 1 0.03 0.03 0 0 0
0
Execute 1 0.00 0.00 0 0 0
0
Fetch 1 0.30 0.30 649 649 4
0
------- ------ -------- ---------- ---------- ---------- ----------
----------
total 3 0.33 0.33 649 649 4
0
Rows Row Source Operation
------- ---------------------------------------------------
0 INDEX FAST FULL SCAN (object id 5286)
Rows Execution Plan
------- ---------------------------------------------------
0 SELECT STATEMENT GOAL: CHOOSE
0 INDEX GOAL: ANALYZED (FAST FULL SCAN) OF 'SYS_C001069' (UNIQUE)
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