Query runs with Index... View Full Scan does...

We have table as:

drop table xml_tbl;

create table xml_tbl)
whole xml_msg_id
xmltype xml_msg_text
);

insert into xml_tbl values
(1, "< principal > < id > 1 < /ID > < / hand > '");

insert into xml_tbl values-(xml_msg_id, xml_msg_text)
(1, "< principal > < id > 2 < /ID > < / hand > '");

There is a hint of XMLType on an XPATH for the xml_msg_text column.

Another table like:

create the table1 Table:
(id1 int);

Insert into Table1 values (2);
Insert into Table1 values (3);

View as follows:

Create or replace view V1 as
Select t.xml_msg_text
of xml_tbl t
where (xmlexists)
' ' fn:collection("oradb:/PUBLIC/TABLE1") / ROW [ID1 = $d/hand/id] ".
from t.xml_msg_text as "d".
);

If I run the query from the view only or
Select t.xml_msg_text
of xml_tbl t
where (xmlexists)
' ' fn:collection("oradb:/PUBLIC/TABLE1") / ROW [ID1 = $d/hand/id] ".
from t.xml_msg_text as "d".
);

XMLIndex has proved to be used in the PLAN to EXPLAIN and I get the result in a few seconds.

WHILE

If I execute Select * from V1 where the view V1 has the same underlying query.
Execution going on indefinitely.
EXPLAIN the PLAN also show that the XML Index is not used, and is it a FTS.
Please suggest.

You should have posted this in the {forum: id = 34} forum, as your previous posts on the subject.

What is the definition of the XMLIndex?

Tags: Database

Similar Questions

Why the optimizer ignores Index Fast full Scan when much lower cost?

Summary (tracking details below) - to improve the performance of a query on more than one table, I created an index on a table that included all the columns referenced in the query. With the new index in place the optimizer is still choosing a full Table Scan on an Index fast full scan. However, by removing the one query tables I reach the point where the optimizer suddenly use the Index Fast Full Scan on this table. And 'Yes', it's a lot cheaper than the full Table Scan it used before. By getting a test case, I was able to get the motion down to 4 tables with the optimizer still ignoring the index and table of 3, it will use the index.

So why the optimizer not chooses the Index Fast Full Scan, if it is obvious that it is so much cheaper than a full Table Scan? And why the deletion of a table changes how the optimizer - I don't think that there is a problem with the number of join permutations (see below). The application is so simple that I can do, while remaining true to the original SQL application, and it still shows this reversal in the choice of access path. I can run the queries one after another, and he always uses a full Table Scan for the original query and Index fast full scan for the query that is modified with a table less.

Watching trace 10053 output for the two motions, I can see that for the original query 4 table costs alone way of ACCESS of TABLE UNIQUE section a full Table Scan. But for the modified query with a table less, the table now has a cost for an Index fast full scan also. And the end of the join cost 10053 does not end with a message about exceeding the maximum number of permutations. So why the optimizer does not cost the IFFS for the first query, when it does for the second, nearly identical query?

This is potentially a problem to do with OUTER joins, but why? The joins between the tables do not change when the single extra table is deleted.

It's on 10.2.0.5 on Linux (Oracle Enterprise Linux). I did not define special settings I know. I see the same behavior on 10.2.0.4 32-bit on Windows (XP).

Thank you
John
Blog of database Performance

DETAILS
I've reproduced the entire scenario via SQL scripts to create and populate the tables against which I can then run the queries. I've deliberately padded table so that the length of the average line of data generated is similar to that of the actual data. In this way the statistics should be similar on the number of blocks and so forth.

System - uname - a

Linux mysystem.localdomain 2.6.32-300.25.1.el5uek #1 SMP Tue May 15 19:55:52 EDT 2012 i686 i686 i386 GNU/Linux

Database - v$ version

Oracle Database 10g Enterprise Edition Release 10.2.0.5.0 - Prod
PL/SQL Release 10.2.0.5.0 - Production
CORE    10.2.0.5.0      Production
TNS for Linux: Version 10.2.0.5.0 - Production
NLSRTL Version 10.2.0.5.0 - Production

Original query (complete table below details):

SELECT 
    episode.episode_id , episode.cross_ref_id , episode.date_required , 
    product.number_required , 
    request.site_id 
FROM episode 
LEFT JOIN REQUEST on episode.cross_ref_id = request.cross_ref_id 
     JOIN product ON episode.episode_id = product.episode_id 
LEFT JOIN product_sub_type ON product.prod_sub_type_id = product_sub_type.prod_sub_type_id 
WHERE (
        episode.department_id = 2
    and product.status = 'I'
      ) 
ORDER BY episode.date_required
;

Execution of display_cursor after the execution plan:

SQL_ID  5ckbvabcmqzw7, child number 0
-------------------------------------
SELECT     episode.episode_id , episode.cross_ref_id , episode.date_required ,
product.number_required ,     request.site_id FROM episode LEFT JOIN REQUEST on
episode.cross_ref_id = request.cross_ref_id      JOIN product ON episode.episode_id =
product.episode_id LEFT JOIN product_sub_type ON product.prod_sub_type_id =
product_sub_type.prod_sub_type_id WHERE (         episode.department_id = 2 and
product.status = 'I'       ) ORDER BY episode.date_required

Plan hash value: 3976293091

-----------------------------------------------------------------------------------------------------
| Id  | Operation             | Name                | Rows  | Bytes |TempSpc| Cost (%CPU)| Time     |
-----------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT      |                     |       |       |       | 35357 (100)|          |
|   1 |  SORT ORDER BY        |                     | 33333 |  1920K|  2232K| 35357   (1)| 00:07:05 |
|   2 |   NESTED LOOPS OUTER  |                     | 33333 |  1920K|       | 34879   (1)| 00:06:59 |
|*  3 |    HASH JOIN OUTER    |                     | 33333 |  1822K|  1728K| 34878   (1)| 00:06:59 |
|*  4 |     HASH JOIN         |                     | 33333 |  1334K|       |   894   (1)| 00:00:11 |
|*  5 |      TABLE ACCESS FULL| PRODUCT             | 33333 |   423K|       |   103   (1)| 00:00:02 |
|*  6 |      TABLE ACCESS FULL| EPISODE             |   299K|  8198K|       |   788   (1)| 00:00:10 |
|   7 |     TABLE ACCESS FULL | REQUEST             |  3989K|    57M|       | 28772   (1)| 00:05:46 |
|*  8 |    INDEX UNIQUE SCAN  | PK_PRODUCT_SUB_TYPE |     1 |     3 |       |  0   (0)|          |
-----------------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------
   3 - access("EPISODE"."CROSS_REF_ID"="REQUEST"."CROSS_REF_ID")
   4 - access("EPISODE"."EPISODE_ID"="PRODUCT"."EPISODE_ID")
   5 - filter("PRODUCT"."STATUS"='I')
   6 - filter("EPISODE"."DEPARTMENT_ID"=2)
   8 - access("PRODUCT"."PROD_SUB_TYPE_ID"="PRODUCT_SUB_TYPE"."PROD_SUB_TYPE_ID")

Updated the Query:

SELECT 
    episode.episode_id , episode.cross_ref_id , episode.date_required , 
    product.number_required , 
    request.site_id 
FROM episode 
LEFT JOIN REQUEST on episode.cross_ref_id = request.cross_ref_id 
     JOIN product ON episode.episode_id = product.episode_id 
WHERE (
        episode.department_id = 2
    and product.status = 'I'
      ) 
ORDER BY episode.date_required
;

Execution of display_cursor after the execution plan:

SQL_ID  gbs74rgupupxz, child number 0
-------------------------------------
SELECT     episode.episode_id , episode.cross_ref_id , episode.date_required ,
product.number_required ,     request.site_id FROM episode LEFT JOIN REQUEST on
episode.cross_ref_id = request.cross_ref_id      JOIN product ON episode.episode_id =
product.episode_id WHERE (         episode.department_id = 2     and product.status =
'I'       ) ORDER BY episode.date_required

Plan hash value: 4250628916

----------------------------------------------------------------------------------------------
| Id  | Operation              | Name        | Rows  | Bytes |TempSpc| Cost (%CPU)| Time     |
----------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT       |             |       |       |       | 10515 (100)|          |
|   1 |  SORT ORDER BY         |             | 33333 |  1725K|  2112K| 10515   (1)| 00:02:07 |
|*  2 |   HASH JOIN OUTER      |             | 33333 |  1725K|  1632K| 10077   (1)| 00:02:01 |
|*  3 |    HASH JOIN           |             | 33333 |  1236K|       |   894   (1)| 00:00:11 |
|*  4 |     TABLE ACCESS FULL  | PRODUCT     | 33333 |   325K|       |   103   (1)| 00:00:02 |
|*  5 |     TABLE ACCESS FULL  | EPISODE     |   299K|  8198K|       |   788   (1)| 00:00:10 |
|   6 |    INDEX FAST FULL SCAN| IX4_REQUEST |  3989K|    57M|       |  3976   (1)| 00:00:48 |
----------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------
   2 - access("EPISODE"."CROSS_REF_ID"="REQUEST"."CROSS_REF_ID")
   3 - access("EPISODE"."EPISODE_ID"="PRODUCT"."EPISODE_ID")
   4 - filter("PRODUCT"."STATUS"='I')
   5 - filter("EPISODE"."DEPARTMENT_ID"=2)

Creating the table and Population:
1 create tables
2. load data
3 create indexes
4. collection of statistics

--
-- Main table
--
create table episode (
episode_id number (*,0),
department_id number (*,0),
date_required date,
cross_ref_id varchar2 (11),
padding varchar2 (80),
constraint pk_episode primary key (episode_id)
) ;
--
-- Product tables
--
create table product_type (
prod_type_id number (*,0),
code varchar2 (10),
binary_field number (*,0),
padding varchar2 (80),
constraint pk_product_type primary key (prod_type_id)
) ;
--
create table product_sub_type (
prod_sub_type_id number (*,0),
sub_type_name varchar2 (20),
units varchar2 (20),
padding varchar2 (80),
constraint pk_product_sub_type primary key (prod_sub_type_id)
) ;
--
create table product (
product_id number (*,0),
prod_type_id number (*,0),
prod_sub_type_id number (*,0),
episode_id number (*,0),
status varchar2 (1),
number_required number (*,0),
padding varchar2 (80),
constraint pk_product primary key (product_id),
constraint nn_product_episode check (episode_id is not null) 
) ;
alter table product add constraint fk_product 
foreign key (episode_id) references episode (episode_id) ;
alter table product add constraint fk_product_type 
foreign key (prod_type_id) references product_type (prod_type_id) ;
alter table product add constraint fk_prod_sub_type
foreign key (prod_sub_type_id) references product_sub_type (prod_sub_type_id) ;
--
-- Requests
--
create table request (
request_id number (*,0),
department_id number (*,0),
site_id number (*,0),
cross_ref_id varchar2 (11),
padding varchar2 (80),
padding2 varchar2 (80),
constraint pk_request primary key (request_id),
constraint nn_request_department check (department_id is not null),
constraint nn_request_site_id check (site_id is not null)
) ;
--
-- Activity & Users
--
create table activity (
activity_id number (*,0),
user_id number (*,0),
episode_id number (*,0),
request_id number (*,0), -- always NULL!
padding varchar2 (80),
constraint pk_activity primary key (activity_id)
) ;
alter table activity add constraint fk_activity_episode
foreign key (episode_id) references episode (episode_id) ;
alter table activity add constraint fk_activity_request
foreign key (request_id) references request (request_id) ;
--
create table app_users (
user_id number (*,0),
user_name varchar2 (20),
start_date date,
padding varchar2 (80),
constraint pk_users primary key (user_id)
) ;

prompt Loading episode ...
--
insert into episode
with generator as 
(select rownum r
          from (select rownum r from dual connect by rownum <= 1000) a,
               (select rownum r from dual connect by rownum <= 1000) b,
               (select rownum r from dual connect by rownum <= 1000) c
         where rownum <= 1000000
       ) 
select r, 2,
    sysdate + mod (r, 14),
    to_char (r, '0000000000'),
    'ABCDEFGHIJKLMNOPQRSTUVWXYZ' || to_char (r, '000000')
  from generator g
where g.r <= 300000
/
commit ;
--
prompt Loading product_type ...
--
insert into product_type
with generator as 
(select rownum r
          from (select rownum r from dual connect by rownum <= 1000) a,
               (select rownum r from dual connect by rownum <= 1000) b,
               (select rownum r from dual connect by rownum <= 1000) c
         where rownum <= 1000000
       ) 
select r, 
       to_char (r, '000000000'),
       mod (r, 2),
       'ABCDEFGHIJKLMNOPQRST' || to_char (r, '000000')
  from generator g
where g.r <= 12
/
commit ;
--
prompt Loading product_sub_type ...
--
insert into product_sub_type
with generator as 
(select rownum r
          from (select rownum r from dual connect by rownum <= 1000) a,
               (select rownum r from dual connect by rownum <= 1000) b,
               (select rownum r from dual connect by rownum <= 1000) c
         where rownum <= 1000000
       ) 
select r, 
       to_char (r, '000000'),
       to_char (mod (r, 3), '000000'),
       'ABCDE' || to_char (r, '000000')
  from generator g
where g.r <= 15
/
commit ;
--
prompt Loading product ...
--
-- product_id prod_type_id prod_sub_type_id episode_id padding 
insert into product
with generator as 
(select rownum r
          from (select rownum r from dual connect by rownum <= 1000) a,
               (select rownum r from dual connect by rownum <= 1000) b,
               (select rownum r from dual connect by rownum <= 1000) c
         where rownum <= 1000000
       ) 
select r, mod (r, 12) + 1, mod (r, 15) + 1, mod (r, 300000) + 1,
       decode (mod (r, 3), 0, 'I', 1, 'C', 2, 'X', 'U'),
       dbms_random.value (1, 100), NULL
  from generator g
where g.r <= 100000
/
commit ;
--
prompt Loading request ...
--
-- request_id department_id site_id cross_ref_id varchar2 (11) padding 
insert into request
with generator as 
(select rownum r
          from (select rownum r from dual connect by rownum <= 1000) a,
               (select rownum r from dual connect by rownum <= 1000) b,
               (select rownum r from dual connect by rownum <= 1000) c
         where rownum <= 10000000
       ) 
select r, mod (r, 4) + 1, 1, to_char (r, '0000000000'),
'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz01234567890123456789' || to_char (r, '000000'),
'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789012345678' || to_char (r, '000000')
  from generator g
where g.r <= 4000000
/
commit ;
--
prompt Loading activity ...
--
-- activity activity_id user_id episode_id request_id (NULL) padding 
insert into activity
with generator as 
(select rownum r
          from (select rownum r from dual connect by rownum <= 1000) a,
               (select rownum r from dual connect by rownum <= 1000) b,
               (select rownum r from dual connect by rownum <= 1000) c
         where rownum <= 10000000
       ) 
select r, mod (r, 50) + 1, mod (r, 300000) + 1, NULL, NULL
  from generator g
where g.r <= 100000
/
commit ;
--
prompt Loading app_users ...
--
-- app_users user_id user_name start_date padding 
insert into app_users
with generator as 
(select rownum r
          from (select rownum r from dual connect by rownum <= 1000) a,
               (select rownum r from dual connect by rownum <= 1000) b,
               (select rownum r from dual connect by rownum <= 1000) c
         where rownum <= 10000000
       ) 
select r, 
       'User_' || to_char (r, '000000'),
       sysdate - mod (r, 30),
       'ABCDEFGHIJKLMNOPQRSTUVWXYZ' || to_char (r, '000000')
  from generator g
where g.r <= 1000
/
commit ;
--

prompt Episode (1)
create index ix1_episode_cross_ref on episode (cross_ref_id) ;
--
prompt Product (2)
create index ix1_product_episode on product (episode_id) ;
create index ix2_product_type on product (prod_type_id) ;
--
prompt Request (4)
create index ix1_request_site on request (site_id) ;
create index ix2_request_dept on request (department_id) ;
create index ix3_request_cross_ref on request (cross_ref_id) ;
-- The extra index on the referenced columns!!
create index ix4_request on request (cross_ref_id, site_id) ;
--
prompt Activity (2)
create index ix1_activity_episode on activity (episode_id) ;
create index ix2_activity_request on activity (request_id) ;
--
prompt Users (1)
create unique index ix1_users_name on app_users (user_name) ;
--
prompt Gather statistics on schema ...
--
exec dbms_stats.gather_schema_stats ('JB')

10053 sections - original query

***************************************
SINGLE TABLE ACCESS PATH
  -----------------------------------------
  BEGIN Single Table Cardinality Estimation
  -----------------------------------------
  Table: REQUEST  Alias: REQUEST
    Card: Original: 3994236  Rounded: 3994236  Computed: 3994236.00  Non Adjusted: 3994236.00
  -----------------------------------------
  END   Single Table Cardinality Estimation
  -----------------------------------------
  Access Path: TableScan
    Cost:  28806.24  Resp: 28806.24  Degree: 0
      Cost_io: 28738.00  Cost_cpu: 1594402830
      Resp_io: 28738.00  Resp_cpu: 1594402830
******** Begin index join costing ********
  ****** trying bitmap/domain indexes ******
  Access Path: index (FullScan)
    Index: PK_REQUEST
    resc_io: 7865.00  resc_cpu: 855378926
    ix_sel: 1  ix_sel_with_filters: 1
    Cost: 7901.61  Resp: 7901.61  Degree: 0
  Access Path: index (FullScan)
    Index: PK_REQUEST
    resc_io: 7865.00  resc_cpu: 855378926
    ix_sel: 1  ix_sel_with_filters: 1
    Cost: 7901.61  Resp: 7901.61  Degree: 0
  ****** finished trying bitmap/domain indexes ******
******** End index join costing ********
  Best:: AccessPath: TableScan
         Cost: 28806.24  Degree: 1  Resp: 28806.24  Card: 3994236.00  Bytes: 0
***************************************

10053 - updated the Query

***************************************
SINGLE TABLE ACCESS PATH
  -----------------------------------------
  BEGIN Single Table Cardinality Estimation
  -----------------------------------------
  Table: REQUEST  Alias: REQUEST
    Card: Original: 3994236  Rounded: 3994236  Computed: 3994236.00  Non Adjusted: 3994236.00
  -----------------------------------------
  END   Single Table Cardinality Estimation
  -----------------------------------------
  Access Path: TableScan
    Cost:  28806.24  Resp: 28806.24  Degree: 0
      Cost_io: 28738.00  Cost_cpu: 1594402830
      Resp_io: 28738.00  Resp_cpu: 1594402830
  Access Path: index (index (FFS))
    Index: IX4_REQUEST
    resc_io: 3927.00  resc_cpu: 583211030
    ix_sel: 0.0000e+00  ix_sel_with_filters: 1
  Access Path: index (FFS)
    Cost:  3951.96  Resp: 3951.96  Degree: 1
      Cost_io: 3927.00  Cost_cpu: 583211030
      Resp_io: 3927.00  Resp_cpu: 583211030
  Access Path: index (FullScan)
    Index: IX4_REQUEST
    resc_io: 14495.00  resc_cpu: 903225273
    ix_sel: 1  ix_sel_with_filters: 1
    Cost: 14533.66  Resp: 14533.66  Degree: 1
******** Begin index join costing ********
  ****** trying bitmap/domain indexes ******
  Access Path: index (FullScan)
    Index: IX4_REQUEST
    resc_io: 14495.00  resc_cpu: 903225273
    ix_sel: 1  ix_sel_with_filters: 1
    Cost: 14533.66  Resp: 14533.66  Degree: 0
  Access Path: index (FullScan)
    Index: IX4_REQUEST
    resc_io: 14495.00  resc_cpu: 903225273
    ix_sel: 1  ix_sel_with_filters: 1
    Cost: 14533.66  Resp: 14533.66  Degree: 0
  ****** finished trying bitmap/domain indexes ******
******** End index join costing ********
  Best:: AccessPath: IndexFFS  Index: IX4_REQUEST
         Cost: 3951.96  Degree: 1  Resp: 3951.96  Card: 3994236.00  Bytes: 0
***************************************

I mentioned that it is a bug related to the ANSI SQL standard and transformation probably.

As suggested/asked in my first reply:
1. If you use a no_query_transformation then you should find that you get the use of the index (although not in the plan you would expect)
2. If you use the traditional Oracle syntax, then you should not have the same problem.

When Oracle make Index Fast full Scan?

Hi all
In this case, Oracle index full scan. Please give the solution with at least two example.
Thank you

Oops,

Spleen it was INDEX FAST FULL SCAN. Then index must be greater:

SQL > create table tbl in select * from dba_objects;

Table created.

SQL > alter table tbl
2 edit object_name not null;

Modified table.

SQL > create index tbl_idx1 on tbl (object_name);

The index is created.

SQL > explain the plan for
2. Select object_name in tbl;

He explained.

SQL > select * from table (dbms_xplan.display);

PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------
Hash value of plan: 2675010997

---------------------------------------------------------------------------------
| ID | Operation | Name | Lines | Bytes | Cost (% CPU). Time |
---------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 69022 | 4448K | 109 (1) | 00:00:02 |
| 1. FULL RESTRICTED INDEX SCAN FAST | TBL_IDX1 | 69022 | 4448K | 109 (1) | 00:00:02 |
---------------------------------------------------------------------------------

Note
-----

PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------
-dynamic sample used for this survey (level = 2)

12 selected lines.

SQL >

SY.

An Android apps runs with Z10 and Simulator, but does not start woth Q10

My worn for Android application works very well with Blackberry 10 Simulator, my housing on the portal is rejected but the application does not launch with Q10, works however with Z10.

I checked my code for all uncaught operators who may cause a failure to start, but could not find.

Do you have ideas on why an application running with Z10 or Simulator would not start with Q10?

Thank you, imre.

The size of the screen was really the question. I put Blackberry 720 x 720 for the emulator, the repeated problem, and I fixed it.

It's all good now!

Problem with Windows Fax and Scan does not connect to the Internal Modem

Just got a new Acer Aspire 5542-5416 computer laptop with Windows 7 64 bit Home Premium, 4 GB of Ram and a 320 GB hard drive. It has a 56 k modem integrated fax of like the old days, but I can't make it work. The laptop did not come with the Windows CD.

If I open the program Windows Fax and Scan, it is not able to connect to the modem. Basically, if I click on tools > fax accounts > Add..., I get a box with 2 choices: to connect to a fax modem or connect to a fax on my network server. When I want to connect a fax modem I get a message that says: an error has occurred. Please, try the operation again later or contact your administrator. It allows me to do this then just clock OK and them I'm right where I started.

While in Windows Fax and Scan, if I click on tools > fax settings... nothing happens. No menu settings or anything ever appears. Quite simply, the program does nothing. If I try tools > Fax Status Monitor... I get a box that says entrance exam status, ready to receive a fax. It has a blue progress bar as something takes over, but it gets about 1/100 to and never goes further or ends. There is no box, but there are 3 buttons: view details, answer call or cancel. If I hit details, I get an empty list. If I click on answer call I get an error that says that the fax service is not available.

If I try tools > Options, general tab has only a single option box is checked: play a sound when come it to new messages. If I try to print a Word or PDF file to a fax using Fax in the printer list, I get the same box with 2 choices: to connect to a fax modem or connect to a fax on my network server, but I get the same error message: an error has occurred. Please, try the operation again later or contact your administrator.

I've searched the Internet high and low for a solution but no luck. There is a lot of discussion about this problem, but none of the solutions work for me. If I go to Device Manager, the modem is working properly and if I click on the Modem query on the Diagnostics tab, it seems to be able to communicate with the modem very well. I tried to roll back the driver and updated again and still no luck, same problem. If I go to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Fax\Accounts in the registry, there is no subkeys under the folder accounts I can delete.

Has anyone else had a similar problem? Is there any solution for this? I did a Windows Update last night and has not yet solve it. Thank you.

Sorry about that.

Here is the link:

http://social.msdn.Microsoft.com/forums/en-us/windowscompatibility/thread/c75ae899-D05B-411D-a7f2-00fdd33b8589/

Reg - full scan limited index

Hi Experts/gurus,
I read Oracle http://docs.oracle.com/cd/B19306_01/server.102/b14211/optimops.htm#i52044 docs, i.e. the difference between the range index scans, full scan and full scan index restricts index. Here is the description of 'Fast Full Index Scans'

Full index scans are an alternative to a full table scan when the index contains all the columns needed for the query, and at least one column in the index key has the NOT NULL constraint. A full scan accesses the data in the index itself, without access to the table. It can be used to eliminate a sort operation, because the data are not classified by the index key. It reads the entire index using multiblock bed, unlike a full index scan and can be parallelized.

Therefore, the document says, the optimizer to choose index FFS, 'at least in the index key column a NOT NULL constraint', but I see less test cases is in complete contrast to what I've read.

I created a table without constraints "NOT NULL".

SQL> create table r_dummy(a number,b varchar2(10));

Table created.

SQL> insert into r_dummy select level,'hi' from dual connect by level<=20;

20 rows created.

SQL> commit;

Commit complete.

SQL> exec dbms_stats.gather_table_stats('HLODS','R_DUMMY');

PL/SQL procedure successfully completed.

SQL> select * from r_dummy where a <= 10;

         A B
---------- ----------
         1 hi
         2 hi
         3 hi
         4 hi
         5 hi
         6 hi
         7 hi
         8 hi
         9 hi
        10 hi

10 rows selected.


Execution Plan
----------------------------------------------------------
Plan hash value: 2533004807

-----------------------------------------------------------------------------
| Id  | Operation         | Name    | Rows  | Bytes | Cost (%CPU)| Time     |
-----------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |         |    10 |    60 |     3   (0)| 00:00:01 |
|*  1 |  TABLE ACCESS FULL| R_DUMMY |    10 |    60 |     3   (0)| 00:00:01 |
-----------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   1 - filter("A"<=10)


Statistics
----------------------------------------------------------
          0  recursive calls
          0  db block gets
          8  consistent gets
          0  physical reads
          0  redo size
        329  bytes sent via SQL*Net to client
        238  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
         10  rows processed

As expected under its weight "Full Table Scan", now if I have an index on columns (a, b), if my interpretation is correct, according to the docs, the optimizer should not do a "full Index scan", but Interestingly, it obeys the indication of index_ffs and did a full scan index

SQL> create index r_dummy_idx on r_dummy(a,b);

Index created.

SQL> exec dbms_stats.gather_index_stats('HLODS','R_DUMMY_IDX');

PL/SQL procedure successfully completed.

SQL> select /*+index_ffs(r)*/ * from r_dummy r where a <= 10;

         A B
---------- ----------
         1 hi
         2 hi
         3 hi
         4 hi
         5 hi
         6 hi
         7 hi
         8 hi
         9 hi
        10 hi

10 rows selected.


Execution Plan
----------------------------------------------------------
Plan hash value: 3219236618

------------------------------------------------------------------------------------
| Id  | Operation            | Name        | Rows  | Bytes | Cost (%CPU)| Time     |
------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT     |             |    10 |    60 |     2   (0)| 00:00:01 |
|*  1 |  INDEX FAST FULL SCAN| R_DUMMY_IDX |    10 |    60 |     2   (0)| 00:00:01 |
------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   1 - filter("A"<=10)


Statistics
----------------------------------------------------------
          1  recursive calls
          0  db block gets
          4  consistent gets
          0  physical reads
          0  redo size
        330  bytes sent via SQL*Net to client
        238  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
         10  rows processed

This clearly shows the optimizer chooses 'INDEX FAST FULL SCAN' even though none of the indexed columns have 'NOT NULL' constraint.

And there is another statement that talks about the results of the COMMAND.

+ "May not be used to eliminate a sort operation, because data are not classified by the index key ' +.

He eliminated the sort operation, I see my results in ascending order.

SQL> drop table r_dummy;

Table dropped.

SQL> create table r_Dummy(a number);

Table created.

SQL> insert into r_dummy values(10);

1 row created.

SQL> insert into r_dummy values(3);

1 row created.

SQL> insert into r_dummy values(1);

1 row created.

SQL> insert into r_dummy values(9);

1 row created.

SQL> insert into r_dummy values(5);

1 row created.

SQL> insert into r_dummy values(4);

1 row created.

SQL> insert into r_dummy values(2);

1 row created.

SQL> insert into r_dummy values(6);

1 row created.

SQL> insert into r_dummy values(7);

1 row created.

SQL> commit;

Commit complete.

SQL> select * from r_dummy;

         A
----------
        10
         3
         1
         9
         5
         4
         2
         6
         7

9 rows selected.

SQL> create index r_dummy_idx on r_dummy(a);

Index created.

SQL> set autotrace on;
SQL> exec dbms_stats.gather_table_stats('HLODS','R_DUMMY');

PL/SQL procedure successfully completed.

SQL> exec dbms_stats.gather_index_stats('HLODS','R_DUMMY_IDX');

PL/SQL procedure successfully completed.

Below you can see the results in ascending order.

SQL> select /*+index_ffs(r)*/ * from r_dummy r where a<=10;

         A
----------
         1
         2
         3
         4
         5
         6
         7
         9
        10

9 rows selected.


Execution Plan
----------------------------------------------------------
Plan hash value: 3219236618

------------------------------------------------------------------------------------
| Id  | Operation            | Name        | Rows  | Bytes | Cost (%CPU)| Time     |
------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT     |             |     9 |    27 |     2   (0)| 00:00:01 |
|*  1 |  INDEX FAST FULL SCAN| R_DUMMY_IDX |     9 |    27 |     2   (0)| 00:00:01 |
------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   1 - filter("A"<=10)


Statistics
----------------------------------------------------------
          1  recursive calls
          0  db block gets
          4  consistent gets
          0  physical reads
          0  redo size
        291  bytes sent via SQL*Net to client
        238  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          9  rows processed

SQL>

I am not sure if the docs are wrong or I'm reading wrong. Please help / correct me if my interpretation is poor.

RUSSO says:
Nicosa salvation,
First of all, thank you for your elaborate explanation.

Nicosa wrote:
Will rely on data to order no order by clause and your app will be one day or the other have a bug. + (which, in fact, will not one, as the app has been designed in this way!) +

I don't really do this, I know that even in parallel the same query may return also rows without a prescription. But was surprised to see my results neatly on INDEX NORMAL (non-partitioned). However, I make sure that I have use 'order by' when I want my results to order.

But still I'm not sure, how the absence of constraint column 'NOT NULL' in the index would stop optimizer to do a full scan limited index

Oracle does not index lines where all coluumns in the index are null. So, in your first example it could be possible that there is a line wiith the two a and b null. Oracle could not return this line using an index full assessment because it would not be in the index. However, by adding a predicate on a indexed columns say you actually column is not null.

In the table, that I used in my example above, all three columns are nullable. Take into account:

SQL> select acctno, count(*) from pttrans
  2  group by acctno;

Execution Plan
----------------------------------------------------------
Plan hash value: 3294770776

--------------------------------------------------------------------------------------
| Id  | Operation          | Name    | Rows  | Bytes |TempSpc| Cost (%CPU)| Time     |
--------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |         |   532K|  6239K|       | 48143   (2)| 00:09:38 |
|   1 |  HASH GROUP BY     |         |   532K|  6239K|   107M| 48143   (2)| 00:09:38 |
|   2 |   TABLE ACCESS FULL| PTTRANS |  5081K|    58M|       | 37895   (1)| 00:07:35 |
--------------------------------------------------------------------------------------

SQL> select acctno, count(*) from pttrans
  2  where acctno is not null
  3  group by acctno;

Execution Plan
----------------------------------------------------------
Plan hash value: 3737827862

------------------------------------------------------------------------------------------
| Id  | Operation             | Name     | Rows  | Bytes |TempSpc| Cost (%CPU)| Time     |
------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT      |          |   532K|  6239K|       | 20641   (4)| 00:04:08 |
|   1 |  HASH GROUP BY        |          |   532K|  6239K|   107M| 20641   (4)| 00:04:08 |
|*  2 |   INDEX FAST FULL SCAN| PTTRANS1 |  5081K|    58M|       | 10393   (2)| 00:02:05 |
------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   2 - filter("ACCTNO" IS NOT NULL)

The first query must examine acctno null to get the correct number, but the second, because I asked explicitly not null can use the index.

John

Smart Scan does not

Hello
My version of the database is 11.2.0.3 64bits RAC environment running on quarter basket exadata. When I ran the SQL below, the plan that got generated showed STORAGE INDEX FAST FULL SCAN also indicated below.
```
select /*+ GATHER_PLAN_STATISTICS*/ count(*) from jarosods.GL_IMPORTREFERENCES_DET a the actual execution is as below
```
Hello

Diluvium readings are eligible for SmartScan only if it is made in direct-path. You don't need to change the DOP, since she can use the direct path read series (according to the size of the segment, how many blocks is in the cache, and how many of them is dirty - see https://fritshoogland.wordpress.com/2013/05/09/direct-path-read-and-fast-full-index-scans/). Even with higer DOP, parallel query may choose to use the cache buffers - so not SmartScan.

Kind regards

Franck.

Query not using Full Scan Index

Hello world
I'm on 11.2.0.3.0 AIX 6.1.
There is a query such as:
Select: sys_b_0 | Count (distinct (column_name)) table;
that goes for the analysis full table. The column was values separate only 104 with not NULL values. To save memory buffer gets, I created an index on the table with the column used in the query (i.e. whose distinct values are recovered).
The problem is that even after the creation of indexes and force the flag index that it does not use the full scan of the index. The provided indication is correct in syntax and was the only clue in the query, so there is no question of conflicts with others.
Can anyone suggest me what I might be missing?
Thank you

It seems to me that if print_branch_code is defined as nullable in the table. If this is the case, the optimizer goes for a sweep of index, even if there is no real NULL values

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http://www.Malwarebytes.org/MBAM.php

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c:\windows\winsxs\x86_microsoft-Windows-font-bitmap-oem_31bf3856ad364e35_6.0.6000.16386_none_fb2d5aefb17b8d65\vga865.FON

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Method 2: you can run Safe Mode security monitor, see the steps in the article below
How to install the free Windows Live OneCare Safety Scanner and then scan your computer in Mode safe

Method 3: Follow the steps mentioned in the link below to check your hard disk for errors, and then check if the problem is resolved
Check your hard drive for errors

If the problem persists,

Method 4: Long file name could cause this problem, perform a backup of the file (copy it somewhere else), and then rename the file, check to see if that makes a difference

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Ajay K

Microsoft Answers Support Engineer
***************************************************************************
Visit our Microsoft answers feedback Forum and let us know what you think.

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