Performance Tuning :: Why Elapsed Time Changed While Execution Plan And Stats Remains The Same

Jun 4, 2010

attached query giving consistent execution plan but different timings across run

SELECT /*+ INDEX (CRT CRT_CUN_FK_I)*/
DISTINCT odr.dve_id
FROM company_requirements crt, orders odr, lelo_products la_pct
WHERE crt.qtn_cun_id = 10035637--10000021--10035667
AND crt.ID = odr.crt_id_quote_implemented
AND NVL (odr.cancellation_date, '31-Dec-9999') = '31-Dec-9999'

[code]....

we have 4 databases, 2 on each servers, such that db1 and db2 on server1 and db3 and db4 on server2

refer count of the records for column of biggest table in the query, taken on all 4 databases (The column is nullable)

select count(*) from company_requirements crt WHERE crt.qtn_cun_id = 10035637
db1 = 73335
db2 = 89073
db3 = 81182
db4 = 82936

First I executed the query on db1 and db2 while there wasn't any user logged on to the system

db1
**********
call count cpu elapsed disk query current rows
------- ------ -------- ---------- ---------- ---------- ---------- ----------
Parse 1 0.06 0.08 0 0 0 0
Execute 1 0.00 0.00 0 0 0 0
Fetch 1 17.47 473.39 85704 1508102 0 0

[code]...

Elapsed times include waiting on following events:

Event waited on Times Max. Wait Total Waited
---------------------------------------- Waited ---------- ------------
SQL*Net message to client 1 0.00 0.00
db file sequential read 85704 0.31 460.55
latch free 1 0.00 0.00
SQL*Net message from client 1 14.98 14.98

[code]...

Why the elasped time changed when data and plan hasn't changed at all? Also why the plan has different stats for round 1 and 2 on db1 and db2?

I ran it 2 times each round each database so hard parsing shall not be issue.Also why the number of rows accessed are different in db1,db2 and db3,db4 especially for step1 when count of crt.qtn_cun_id is similar?

In fact when the query was taking long I was the only user on the system Also I used hard coded value (no bind variables at all)

I checked num_rows, distinct keys as well which are quite similar across all 4 databases Also no stats where gather during the query execution

What I should have checked or monitored?

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Performance Tuning :: Avg Time Taken By Execution Plan

Apr 12, 2013

How can i check the avg time taken by an execution plan. Actually i have a very big query and it changes its execution plan very often, we would like to lock the best execution plan and to find it , i would like to know the Average Execution Time the query takes when it runs using different different execution plans.

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Performance Tuning :: Using Stats Table Instead Of Regular Stats To Get Plan?

Jan 27, 2011

DBMS_STATS.CREATE_STATS_TABLE
DBMS_STATS.EXPORT_SCHEMA_STATS
DBMS_STATS.GATHER_TABLE_STATS

I have used the above to get a copy of schema stats and gather new stats for specific tables into a STATS TABLE in my personal schema. What I want to do now is use this stats table to generate plans for queries where I believe stats are off. Is it even possible? To be clear, I do not want to import stats because this replaces the stats currently there. I just want to point the CBO to my stats table for generating plans.

there was a session parameter I could set to tell oracle to use my stats table when generating plans, or an explain plan clause I could use or a DBMS_XPLAN paramter I could provide that would tell these tools to use my stats table when generating a plan, or even some way to tell autotrace. But I have found none of this.

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Aug 6, 2012

Our UNDO space remains at a high level 85 to 95 percent. We keep adding database files and it doesn't seem to go down significantly. When we do a backup of the system where we shut the database down, it does go down some but then within a week or so it is back up again.

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Performance Tuning :: Different Execution Plan In Different DB

Jul 20, 2013

Why the query is behaving differently with the different database.(execution plan)

Whatever the production database is having same database instance replicated to a new schema. I tried both the queries running on both environment.In prod the index has been used but in newdev it is not. This case existing primary key index were not been used.

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Performance Tuning :: SQL Ordered By Elapsed Time

Feb 2, 2013

Elapsed Time (s)CPU Time (s)Executions Elap per Exec (s) % Total DB TimeSQL IdSQL ModuleSQL Text

3,263 32 1 3263.49 2.79 3ta0ms19fvgds httpd.exe SELECT CASE WHEN COUNT >= 1...Elapsed
6,360 164 2 3180.17 5.44 51jx99dm0swv7 cpm_srvscript@ahcaxasmil1b (TNS V1-V3) SELECT /*+ CCL<PFT_GET_RP...

On AWR, I see two script that are out of ordinary, and I want to make sure that I interpret them correctly.

1) "Elap per Exec (s)" shows 3263.49 with 1 "Executions".
2) "Elap per Exec (s)" shows 3180.17 each execution with 2 "Executions".

Does this mean that this script ran for ~ 54 minutes (3263.49 / 60 seconds) for 1 "Execution" and ~ 53 minutes (3180.17 / 60 seconds) per each execution? I need to understand "Elapsed Time (s),CPU Time (s),Executions ,Elap per Exec (s), % Total DB Time" represent.

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Performance Tuning :: Execution Plan Of SQL Statement

Mar 25, 2012

I have queries on the execution plan of a sql statement

Following is the example

create table t1 as select s1.nextval id,a.* from dba_objects a;
create table t2 as select s2.nextval id,a.* from dba_objects a;
insert into t1 select s1.nextval id,a.* from dba_objects a;
insert into t1 select s1.nextval id,a.* from dba_objects a;
insert into t2 select s2.nextval id,a.* from dba_objects a;
insert into t2 select s2.nextval id,a.* from dba_objects a;
insert into t2 select s2.nextval id,a.* from dba_objects a;
commit;

create index i1 on t1(id);
create index i2 on t2(id);
create index i11 on t1(object_type);

exec dbms_stats.gather_table_stats(user,'T1',cascade=>true);
exec dbms_stats.gather_table_stats(user,'T2',cascade=>true);

select count(*) from t1 where object_type='VIEW';

COUNT(*)
----------
8934

set autotrace traceonly explain

Can we say in the following case, that,

(1) First index on object_type is accessed to get rowids - t1.object_type='VIEW'
(2) Then the filter on owner is applied - t1.owner='SYS'
(3) Then the table T1 is accessed to fetch data from the rowids returned by the index I11 and filer application - TABLE ACCESS BY INDEX ROWID

Though I am unable to understand how filter can be applied to the rowids retrieved from index, we can see from the plan below that The rows accessed have reduced from 8550 to 1221 before we access the table...Thus filter "t1.owner='SYS'" is applied in between. Right?

another question is

Case 1 - do we retrieve a rowid from index for a given value, then retrieve required values from table for that rowid
Thus row at a time in both ... in loop
OR
Case 2 - we first fetch all rowids from index and then retrieve values from table one row at a time from the collection of rowids fetched?

Suppose Case 1 is what is happening then can we say, both the steps mentioned by IDS 2,3 in plan below are executed exactly equal number of times and the filter "t1.owner='SYS'" is applied at some later stage? Of course in this case the values in ROWS stand misleading then

select * from t1,t2 where t1.id = t2.id and t1.object_type='VIEW' and t1.owner='SYS';

Execution Plan
----------------------------------------------------------
Plan hash value: 26873579
-------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1221 | 233K| 915 (1)| 00:00:11 |
|* 1 | HASH JOIN | | 1221 | 233K| 915 (1)| 00:00:11 |
|* 2 | TABLE ACCESS BY INDEX ROWID| T1 | 1221 | 116K| 381 (1)| 00:00:05 |
|* 3 | INDEX RANGE SCAN | I11 | 8550 | | 24 (0)| 00:00:01 |
| 4 | TABLE ACCESS FULL | T2 | 161K| 15M| 533 (1)| 00:00:07 |
-------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - access("T1"."ID"="T2"."ID")
2 - filter("T1"."OWNER"='SYS')
3 - access("T1"."OBJECT_TYPE"='VIEW')

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Performance Tuning :: SQL Execution Plan Different On Different Hardware

Oct 31, 2012

So the situation is like this

- Database A (20 tables)
- Database B (20 tables)

- Both A and B are Oracle 11gR2

- Both of these databases run on different hardware (A is a VM, B is on a physical host)

- The 20 tables in A and B have exactly same number of rows and after preparing the data, the schemas were analysed using the same DBMS_STATS parameters

Despite this, the execution plans appear to be quite different for the same queries between A and B

I imagine there is something outside of the Oracle table rowcounts, table stats, column stats, index stats that's resulting in the different execution plans.

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Performance Tuning :: Achieve Same Execution Plan?

Apr 30, 2012

refere to below 2 queries and their execution plans:

First Query
INSERT INTO temp_vendor(vendor_record_seq_no,checksum,rownumber,transaction_type,iu_flag)
SELECT /*+ USE_NL ( vd1 ,vd2 ,vd3 ) leading ( vd1 ,vd2 ,vd3 , tvd) */
vd1.vendor_record_seq_no, tvr.checksum, tvr.rownumber, tvr.transaction_type, 'U'
FROM vendor_data vd1,

[code]...

Second Query
SELECT vd1.vendor_record_seq_no, tvr.checksum, tvr.rownumber, tvr.transaction_type, 'U'
FROM ( select * from vendor_data vd1
where vd1.study_seq_no = 99903
AND vd1.control_column_seq_no = 435361232

[code]...

Both are to achieve same output but written in different ways. CAn I get same exectuion plan from 1st query as there is for 2nd using hints

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May 5, 2011

why different elapsed time in Oracle9i and oracle10g for the same query ?

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Performance Tuning :: SQL Ordered By Elapsed Time And SQL Module?

Feb 24, 2013

Elapsed Time (s) CPU Time (s) Executions Elap per Exec (s) % Total DB Time SQL Id SQL Module SQL Text
2,423 1 3,919 0.62 1.83 gt49gg0fnc5x8 srv_dr@ahs (TNS V1-V3) UPDATE /*+ CCL<OENDB_FILE...
2,227 14 1 2227.16 1.68 bggfx8a04prj9 SQL*Plus select * from (select n.source...
.........

On [SQL ordered by Elapsed Time], [SQL Module] shows an indication that a SQL was executed by which process (i.e. srv_dr@ahs)outside of SQL*PLUS.If [SQL Modeule] shows as [SQL*Plus], does it mean the query was run in SQL*PLUS manually or directly?I have the SQL ID. How do I find out who, how, and exactly what time it was run?

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Performance Tuning :: Execution Plan Changing With Same SQL Profile

Mar 5, 2013

One of our clients is using Rule Based Optimizer on Oracle 10.2.0.3.0

2-3 weeks backs, during performance issue in one of the sql queries, one of our team members executed tuning adviser for it, created SQL profile and the subsequent execution of the SQL did not took much time (less I/O). Now it took hardly a minute to execute

When this happened I checked that the SQL profile forced that particular query to use CBO (say plan_hash_value is PHV1 here). Yesterday the same query again took 15-20 minutes for execution. I checked that even for this execution the query used the same SQL profile but "this time" with different plan_hash_value - say PHV2.

Today again the query executed in less than a minute and used the plan_hash_value as PHV1.

select distinct plan_hash_value,timestamp from dba_hist_sql_plan where sql_id='mysqlid' order by 1,2;

PLAN_HASH_VALUE TIMESTAMP
--------------- --------------------
890360113 20-feb-2013 16:38:39
3736413466 04-mar-2013 08:12:52
1237282258 03-jan-2013 17:15:02

I confirmed from awrsqrpt as well that different plans were used for different plan_hash_values and every time same SQL profile was used

SQL> select name,CATEGORY,SIGNATURE,CREATED,LAST_MODIFIED,TYPE,STATUS,FORCE_MATCHING from dba_sql_profiles;

NAME CATEGORY SIGNATURE CREATED LAST_MODIFIED TYPE STATUS FOR
------------------------------ ------------------------------ ---------- -------------------- -------------------- --------- -------- ---
SYS_SQLPROF_015ffffcc3e1c5b000 DEFAULT 1.5512E+19 20-feb-2013 16:30:48 20-feb-2013 16:30:48 MANUAL ENABLED NO

I am unable to understand how execution plan and thus plan_hash_value is changing for the same SQL Profile. I read that SQL Profile (unlike stored outline) keeps up with increasing data volume and may not keep up with changing data distribution.

I checked that values for 4 bind variables out of 81 are different for execution between today and yesterdays' run(queried v$sql_bind_capture based on last_captured)

My questions are
1) does the different plan_hash_values with different execution plans for query using same SQL profile mean the query was hard parsed multiple times and still used the same SQL profile?
2) If that is the case why I never saw child_number = 1 in any of the views for the same sql_id. I tried it repeatedly over last 2 weeks and always found child_number=0 in v$sql (also loaded_versions=1)
3) Does the different values of bind variable are causing this flip-flop of the plans? How can I conclude this?

I have 2 plans with 2 different plan_hash_values. I know which would be better. How can I force the sql to use better plan in the two in this case where I am using Rule Based Optimizer and have SQL profile created If this is not possible then how can I create stored outline from the existing plan (not waiting for subsequent execution to take place).

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Jan 13, 2011

find the attached tkprof'ed file of session

I started the trace after the query started (upon user's complaint)

However even after tracing the session for more than 30 minutes I am not geeting where the 30 minutes are accounted in this file

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Nov 16, 2011

I executed a query which executed quickly (1.7 seconds) but since its output took time in displaying on the console the time shown by 'set timing on was 39.5 seconds

also I took trace (tkprof) for the same.My query is why the timings under 'Total Waited' (43.19 and 1.69) are not added to the elapsed time 1.83 seconds

call count cpu elapsed disk query current rows
------- ------ -------- ---------- ---------- ---------- ---------- ----------
Parse 1 0.00 0.00 0 0 0 0
Execute 1 0.00 0.06 0 10 0 0
Fetch 758 0.03 1.77 0 0 0 11345
------- ------ -------- ---------- ---------- ---------- ---------- ----------
total 760 0.03 1.83 0 10 0 11345
[code]....

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Performance Tuning :: How To Change Execution Plan Of Currently Executing Statement

Feb 8, 2011

refer following sql statements and code

Session 1
create table tab1 as select * from dba_objects where object_id is not null;
alter session set events '10046 trace name context forever, level 12';
declare
x number;
begin
for i in 1..4
loop

[code]....

Session 2

after "starting" the above pl/sql block from Session 1, I keep on querying tab2 from Session 2 And as soon as 2 records are inserted in tab2, I create index from Session 2

select * from tab2;
select * from tab2;
select * from tab2;
N
----------
1
2
create index i on tab1(object_id);

As I have tested from a single session (just before this test) such index is used for the sql statement

select count(1) into x from tab1 where object_id=2331;

However when I checked the trace file I am not geeting results as expected

I am expecting 4 execution plans - 2 FTS and 2 Index Access scans and for this I am issuing following command

tkprof dst1_ora_7369.trc dst1_ora_7369.txt aggregate=no sys=no

But unfortunately I am getting following output

SELECT COUNT(1)
FROM
TAB1 WHERE OBJECT_ID=2331
call count cpu elapsed disk query current rows
------- ------ -------- ---------- ---------- ---------- ---------- ----------
Parse 1 0.00 0.00 0 1 0 0
Execute 4 0.00 0.00 0 2 0 0

[code]....

1) Why I am unable to see 4 execution plans - 2 with FTS and 2 with Index access when I mentioned 'aggregate=no'?

2) Whether the index i will be used for last 2 iterations after first 2 iterations of FTS?

If answer to above question 2) is 'No'

By which method I can force an ongoing sql statement in loop to take different execution path? Of course I can't hard parse sql in 'that' current session Will flushing Shared pool work in above case?

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Jul 21, 2010

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I have looked at the explain plans, and it has shown me what I think is the problem. On one instance, it does a join on two tables, then runs the other filter/access predicates. On the other instance it runs the filter/access predicated first, then does the expensice join. The one that does the join first is the one that takes around 200 seconds. How to tell Oracle to make this join after runnning the other predicates?

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May 18, 2010

Can we have same execution plan for a create table statement where the name of the table changes every time as follows:

create table test
as
select * from t1

Here table name changes from test to another table name next time

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Mar 20, 2012

Which step in the following plan is the first step of execution

I reckon it is "TABLE ACCESS BY INDEX ROWID| BANK_BATCH_STATE"

Is that correct?

In the "Predicate Information (identified by operation id):"

section the predicates - access and filter for the step "TABLE ACCESS FULL | PYMNT_DUES" are displayed first

Isn't there any relation between the order of execution steps and the order in which predicates are displayed?

Execution Plan
----------------------------------------------------------
Plan hash value: 538700484
-------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
-------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 2364 | 15 (14)| 00:00:01 |
|* 1 | FILTER | | | | | |
| 2 | HASH GROUP BY | | 1 | 2364 | 15 (14)| 00:00:01 |
| 3 | NESTED LOOPS | | 1 | 2364 | 14 (8)| 00:00:01 |
| 4 | NESTED LOOPS | | 1 | 2313 | 13 (8)| 00:00:01 |
| 5 | NESTED LOOPS | | 1 | 2281 | 12 (9)| 00:00:01 |
| 6 | NESTED LOOPS OUTER | | 1 | 2255 | 11 (10)| 00:00:01 |
|* 7 | HASH JOIN | | 1 | 175 | 6 (17)| 00:00:01 |
|* 8 | INDEX RANGE SCAN | INDX_2 | 12 | 612 | 2 (0)| 00:00:01 |
|* 9 | TABLE ACCESS FULL | PYMNT_DUES | 43 | 5332 | 3 (0)| 00:00:01 |
| 10 | VIEW PUSHED PREDICATE | | 1 | 2080 | 5 (0)| 00:00:01 |
| 11 | NESTED LOOPS | | 1 | 154 | 5 (0)| 00:00:01 |
| 12 | NESTED LOOPS | | 1 | 103 | 4 (0)| 00:00:01 |
|* 13 | TABLE ACCESS BY INDEX ROWID| BANK_BATCH_STATE | 1 | 32 | 2 (0)| 00:00:01 |
|* 14 | INDEX RANGE SCAN | INDX_BBS_1 | 3 | | 1 (0)| 00:00:01 |
|* 15 | TABLE ACCESS BY INDEX ROWID| DAILY_CHECK | 1 | 71 | 2 (0)| 00:00:01 |
|* 16 | INDEX RANGE SCAN | INDX_SEARCH | 1 | | 1 (0)| 00:00:01 |
|* 17 | INDEX RANGE SCAN | INDX_2 | 1 | 51 | 1 (0)| 00:00:01 |
|* 18 | INDEX RANGE SCAN | INDX_IAM_SR_NO | 1 | 26 | 1 (0)| 00:00:01 |
|* 19 | INDEX RANGE SCAN | INDX_2 | 1 | 32 | 1 (0)| 00:00:01 |
|* 20 | INDEX RANGE SCAN | INDX_2 | 1 | 51 | 1 (0)| 00:00:01 |
-----------------------------------------------------------------

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Jul 11, 2013

The problem was describe:

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- Second time to execute: Using only indexes on first table, full table scan on the other

- Third time to execute: Do FTS on both of tables.

Now, I show the objects and relate information here:

The Tables:

system@dbwap> select count(*) from my_wap.news_relation;

COUNT(*)
----------
272708

system@dbwap> select count(*) from my_wap.news_content;

COUNT(*)
----------
95092

system@dbwap> desc my_wap.news_content;
Name Null? Type
----------------------------------------------------- -------- ----------------
ID NOT NULL NUMBER(11)
SUBJECT NOT NULL VARCHAR2(500)
TITLE VARCHAR2(4000)
STATE NUMBER(1)
IMGPATH VARCHAR2(500)
ALIGN VARCHAR2(10)

[Code]....

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Mar 9, 2010

In my code I am using delete statement which is taking too much time to execute.

Statement is as follow:

DELETE FROM TRADE_ORDER_EMP_ALLOCATION T
WHERE (ARTEMIS_SOURCE_SYSTEM_ID,NM_ARTEMIS_SOURCE_SYSTEM,CD_BOOK_KEY,ACTIVITY_DT)
IN (SELECT ARTEMIS_SOURCE_SYSTEM_ID,NM_ARTEMIS_SOURCE_SYSTEM,CD_BOOK_KEY,ACTIVITY_DT
FROM LOAD_TRADE_ORDER
WHERE IND_IS_BAD_RECORD='N');

Tables Used:
oTRADE_ORDER_EMP_ALLOCATION Row count (329525880)
oLOAD_TRADE_ORDER Row count (29281)

Every column in "IN" clause and select clause is containing index on it

Every time no of rows which to be deleted is vary (May be in hundred ,thousand or hundred thousand )so that I am Unable to use "BITMAP" index on the table "LOAD_TRADE_ORDER" column "IND_IS_BAD_RECORD" though it is containing distinct record in it.

Even table "TRADE_ORDER_EMP_ALLOCATION" is containing "RANGE" PARTITION over it on the column "ARTEMIS_SOURCE_SYSTEM_ID". With this I am enclosing table scripts with Indexes and Partitions over it.

way for fast execution in of above delete statement?

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Dec 24, 2012

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SELECT ancestor,
Max(D.alarmstate) ALARMSTATE,
Max(D.sialarmstate) SIALARMSTATE,
Max(D.uncralarmstate) UNCRALARMSTATE,
Max(M.commstate) COMMSTATE,
Max(M.nncommstate) NNCOMMSTATE,
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Max(M.abnormal) ABNORMAL,
CASE
[code]....

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Oct 26, 2010

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Aug 8, 2013

Is it possible for the DBMS_STATS "LIST STALE" command to show a stale partition but NOT have its table show as stale?

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so if this is the case, when would I need to run stats on the full partitioned table if running it on the partitions themselves removes the staleness of the table?

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Jun 2, 2011

I am gathering stats by using below block i.e., for some 3 million records and there are 6 indexes on the table. What is the relevance of value 4 here (i.e., method_opt => 'FOR ALL INDEXED COLUMNS SIZE 4')? If I increase 4 to 250 will there be any speed change in gathering stats. My intention is to speed up the gathering of stats.

begin
dbms_stats.gather_table_stats(
ownname => SYS_CONTEXT('USERENV', 'CURRENT_SCHEMA'),
tabname => 'LEGAL_VIEW_TARGET',
method_opt => 'FOR ALL INDEXED COLUMNS SIZE 4',
cascade => TRUE
);
END;

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Jun 15, 2012

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How can this be achieved in 9i, currently I am simply obtaining the SQL_TEXT and then running an explain plan ("EXPLAIN PLAN FOR..") - I believe this is not necessarily the same explain plan that will be used for the sql that is executing though

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Jul 31, 2013

I have a Datamart DB which has a continuously increasing volume. I run a daily optimize job, to have the data analysed using the below:-

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analyze table xxx.abc compute statistics; But this optimization itself is taking nearly 4 hrs to complete and I can't afford to have the delay.

Is there a better way of running this optimization?

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May 24, 2012

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SQL> explain plan for SELECT /*+ FULL(t) */ COUNT(*) FROM "DREAM"."CONSUMER.TAB" t WHERE ROWNUM <= 1000000;
explain plan for SELECT /*+ FULL(t) */ COUNT(*) FROM "DREAM"."CONSUMER.TAB" t WHERE ROWNUM <= 1000000
*
ERROR at line 1:
ORA-01031: insufficient privileges

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May 16, 2011

I have several databases that i've recently upgraded from 9i to 11g. With all of them, the automatic stats gathering process has worked just fine every night during the maintenance window.

However, i have this other database that i created and it seems that the only stats being gathered are on the sys and system schemas and not the actual schema that holds all of our tables.

I did some searching, but i'm not sure i was using the right search terms, because i came up empty.

BANNER
-----------------------------------------------------------------------
Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - 64bit Production
PL/SQL Release 11.2.0.1.0 - Production
CORE 11.2.0.1.0 Production
TNS for Solaris: Version 11.2.0.1.0 - Production
NLSRTL Version 11.2.0.1.0 - Production

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