Performance Tuning :: Adaptive Cursor Sharing VS SPM?
Nov 5, 2013
we are using Release 11.2.0.3.0 of oracle. And have cursor_sharing default setup as 'exact'.
In case of 'sql queries' using bind variable, which suffers performnace issue(unstabilized plan) due to different bind values at runtime addition with skewed columns. In these cases 'adaptive cursor sharing', will monitor major variation in selectivity/cost of multiple available plan(path of execution) and automatically switch to optimum plan during run time query execution.
my question is , considering 'up to date stats for all our database objects' what is the requirement of sql plan baseline(spm)? At which situation ,ACS(adaptive cursor sharing) won't able to stabilize the query plan, so that we have to go for baseline or SPM?
View 2 Replies
ADVERTISEMENT
Dec 18, 2012
I have a table "t", with a highly skewed ID column
Cursor_sharing=force
select count(*) from t;
--79003
select count(*) from t where id=1;
--79002
select count(*) from t where id=99;
--1
I have a index on id column and since highly skewed data is there in id column therefore histogram is there
SQL> select table_name,column_name,histogram,num_buckets from user_tab_cols where table_name='T';
TABLE_NAME COLUMN_NAME HISTOGRAM NUM_BUCKETS
------------------------------ ------------------------------ --------------- ------------
T ID FREQUENCY 2
When i use literals , explain plan comes up with optimal execution plan
select * from t where id=1;
Full table scan
Select * from t where id=99;
Index range scan
But when i use bind variables,sub optimal execution plan
For id=1, it should use Full table scan but it goes for Index range scan , WHY? why ACS is not getting kicked?
alter system flush shared_pool;
set autotrace traceonly
variable n number;
exec :n=1;
select * from t where id=:n;
[code]...
Why is_bind_sensitive not "Y"?
View 10 Replies
View Related
Jul 5, 2012
I am on 11.2.0.2 (RHEL 5.4)
For one of my OLTP table, we have skewed distribution on STATUS column and hence we created frequency histograms. NDV=7 for this column.
My question is : Do we need to have "_optim_peek_user_binds" set to TRUE in order to utilize Adaptive Cursor Sharing ?I have gone through different OTN forum and blogs and it appears that in order to generate different plans, Oracle has to Peek the value of bind variables each time. Without Peeking, how would CBO knows whether to generate new plans or not ?
For xyz reasons, optimpeek_user_binds is set to FALSE in my database and i could not find any sql_id having V$SQL.IS_BIND_AWARE='Y'.
View 9 Replies
View Related
Feb 22, 2011
In an OLTP environment what cursor_sharing setting is preferred?Though typically we retain the original setting for most of the parameters except memory settings etc. I have queries in the following context
No. I am not facing any issue as of now (I am not supporting any Live environment) But I want to know the desgn considerations
First of all in OLTP environment (say one I am referring) we use pl/sql variables which are obviously bind variables Only in case where plan is expected to change we use hard coded values like 'CREDIT' or 'DEBIT' etc. for acc_type column
Again there can be 2 scenario
1) we use the same query for both acc_type values
2) we use 2 different queries
IF v_parameter = 'CR'
select * from accounts where acc_type='CREDIT'...
else
select * from accounts where acc_type='DEBIT'...
end if;
Again suppose the values are skewed and we gather stats with histograms hereIs't it the setting 'cursor_sharing=similar' which will be useful in above case?as with this setting optimizer will 'think' which plan to pick depending upon the values and bind variable peeking is taken care in option 2 above with IF ELSE clause?
BTW
I have carried several tests but not getting conclusive results For example I created following table with skewed data, created index and gather stats with histogram
SQL> select object_id,count(*) from skewed_data_tab group by object_id;
OBJECT_ID COUNT(*)
---------- ----------
5 30
6 2970
7 10797
8 150000
9 300000
SQL> create index i_skewed_tab_data on skewed_data_tab(object_id);
SQL> exec dbms_stats.gather_table_stats(user,'SKEWED_DATA_TAB',cascade=>true,
method_opt=>'for all columns size 254');
Then traced with following options
1) alter session set events '10046 trace name context forever, level 12';
SQL> begin
for i_outer in(select n from ids order by tstamp)
loop
for i_inner in (select /* for exact */ object_id,object_name,object_type
from skewed_data_tab where object_id=i_outer.n)
[code]...
2) set termout off
alter session set events '10046 trace name context forever, level 12';
@/u04/scripts/exact.sql 5
cat /u04/scripts/exact.sql
select /* for exact */ object_id,object_name,object_type from skewed_data_tab where object_id=&1;
But not getting consistent results
View 11 Replies
View Related
Jul 21, 2010
I've been examining som old queries in an existing db due to more and more problems regarding performance. The sql is used as backend for a java/jboss web application with the possibility for users to enter data. With more and more data, there starting to come complaints about the performance.
I stumbled upon a select query with an embedded cursor similar to this :
select id, name ...,
cursor(select id, sequence.... from table2),
cursor(select id, name.... from table3)
from table1
join table4 on (table1.id = table4.id)
where .....
The javacode is a prepared statement with the actual sql as a string and the content of the cursors saved in conjunction with each row.
when i use sqldeveloper to show the explain plan without the cursors, the cost is 2428
when i use sqldeveloper to show the explain plan with just 1 of the cursors, the cost is ~165000
Is there a better way to do this instead of cursors ?
View 2 Replies
View Related
Aug 28, 2013
Does parallel hint works in cursor queries? The cursor query is something like :
cursor c is
select /*+ parallel(s,8) */
from table ref_tab s ---- >>
<where condition>;
The table ref_tab hold data for a single day at any point of time and gets truncate before loading the next days data.On average the table holds around 7 million rows and doesn't contains any index (think that's fine as all together we are loading the whole set).And, we are using bulk logic with save exceptions to open the cursor and load the data into the target table.
View 13 Replies
View Related
Jul 12, 2010
Looking to understand the difference between instance tuning and database tuning.
What is the difference between these two tuning exercises? I understand that an instance is memory based structures (logical) where as database consists of physical structures.
However, how does one tune a database the physical structure? Does it have to do with file placements/block sizes etc. Would you agree that a lot of that is taken care by ASM now in 11g? What tools are required/available (third party as well as oracle supplied) for these types of tuning scenarios?
View 1 Replies
View Related
Oct 31, 2011
I have two tables with 113M records in DWH_BILL_DET & 103M in prd_rerate_chg_que and Im running following merge query, which is running for 13 hrs to update records, which is quiet longer time.
SQL> explain plan for MERGE /*+ parallel (rq, 16) */
INTO DWH_BILL_DET rq
USING (SELECT rated_que_rowid,
detail_rerate_flag_code,
rerate_sel_key,
[code].....
View 39 Replies
View Related
Sep 30, 2010
How the length of column width effects index performance?
For example if i had IOT table emp_iot with columns:
(id number,
job varchar2(20),
time date,
plan number)
Table key consist of(id, job, time)
Column JOB has fixed list of distinct values ('ANALYST', 'NIGHT_WORKED', etc...).
What performance increase i could expect if in column "job" i would store not names but concrete numbers identifying job names.
For e.g. i would store "1" instead 'ANALYST' and "2" instead 'NIGHT_WORKED'.
View 24 Replies
View Related
Jun 16, 2010
I have a question about database fragmentation.I know that fragmentation can reduce performance in query times. The blocks are distributed in many extents and scans process takes a long time. Oracle engine have to locate the address of the next extent..
I want to know if there is any system view in which you can check if your table or index has high fragmentation. If it's needed I will have to re-create, move or rebulid the table or index, but before I want to know if the degree of fragmentation is high.
Any useful script or query to do this, any interesting oracle system view?
View 2 Replies
View Related
Oct 20, 2010
There is a simple way to increase the performance of a query by reducing the row-size of the table it hits. I used it in the past by dividing the table into smaller parts and querying respective smaller table in each query.
what is this method called ? just forgot the method and can't recall it. what this type of row-reduction optimization is called ?
View 6 Replies
View Related
Jun 16, 2011
How many records could I have in a single table without performance degradation with Standard Edition without partitioning with cutting-edge server (8 or 12 cores, 72 GB RAM, FC 4 Gbit, etc...) and good storage?
300 Millions in only one table with 500K transactions / day is too much?
Simple database with simple schema.
How many records begin to be too many?
View 2 Replies
View Related
Nov 15, 2010
Testing our 9i to 11g upgrade, we've imported the entire DB into the new machine.We've found that certain procedures are really suffering performance problems. BUT, we've also found, that if we check out a production copy of the procedure from our source code control, and reinstall it, the performance issue goes away. Just alter the procedure and recompiling does NOT work.
The new machine where the 11g database exists is slightly different than the source, but it's not like we have this problem with every procedure. It's only a couple.
any possible reason that we'd have to re-install a procedure to correct a performance problem?
View 13 Replies
View Related
Apr 12, 2013
I need to check the package performance and need to improve the package performance.
1. how to check the package performance(each and every statement in the package)?
2. In the package using the delete statement to delete all records and observed that delete is taking long time to delete all the records in the table(Table records 7000000). This table is like staging table.Daily need to clean the data before inserting the data into it. what can I use instead of Delete.
View 13 Replies
View Related
Aug 9, 2010
Somewhere I read that we should not use hints in Oracle production environments, but we can use hints in the development environment and on achieving the desired execution plan we can adjust the 'statistics' to follow that plan without hints.
Q1. If it is true what statistics do we adjust for influencing the execution plan and how?
For example, I have the following simple query:
select e.empid, e.ename, d.dname
from emp e, dept d
where e.deptno=d.deptno;
emp.empid, emp.deptno and dep.deptno columns have indexes and the tables have the standard structure as found in the basic oracle examples.
If I look at the execution plan of the above query then I see that the driving table is empand the driven table is dept.Also the type of join that is taking place is 'Nested Loop'.
Questions: With respect to the above query,
Q 2. If I want to make dept the driving table and emp the driven table then how can I adjust the statistics to achieve that?
Q 3. If I want to use hash join instead of a nested loop join then then how can I adjust the statistics to achieve that?
I can put the ordered and the use_hash hint to effect this but again I have heard that altering statistics is a more robust way to control an execution plan as compared to hints.
View 6 Replies
View Related
Dec 6, 2011
I have an issue with export(expdp).
When i exporting an user using expdp utility, the load the on the server is going up-to 5. The size of the database is 180GB. Below is the command that i use for export.
expdp sys/xxxx directory=dbpdump dumpfile=expdp_trk_backup.dmp logfile=expdp_trk_backup.log exclude=statistics schemas=trk
Do i need any look into any memory parameters for this?
View 1 Replies
View Related
Oct 17, 2011
The following query gets input parameter from the Front End application, which User queries to get Reports.There are many drop down boxes like LOB, FAMILY, BRAND etc., The user may or may not select values from drop down boxes.
If the user select any one or more values ( against each drop down box) it has to fetch all matching values from DB. If the user does'nt select any values it has to fetch all the records, in this case application will send a value 'DEFAULT' (which is not a value in DB ) so that the DB will fetch all the records.
For getting this I wrote a query like below using DECODE, which colleague suggested that will hamper performance.From the below query all the variables V_ are defined in procedure which gets the values selected by user as a comma separated string here V_SELLOB and LOB_DESC is column in DB.
DECODE (V_SELLOB, 'DEFAULT', V_SELLOB, LOB_DESC) IN
OPEN v_refcursor FOR
SELECT /*+ FULL(a) PARALLEL(a, 5) */
*
FROM items a
WHERE a.sku_status = 'A'
[code]...
View 9 Replies
View Related
Sep 3, 2010
what the principal things to look at when we have for the same query different performance results are?I have 2 different bases: the plan and data are the same but performance results are very differents.
View 10 Replies
View Related
Mar 17, 2012
are the most important performance keys we have to calculate or take in account to preserve or to increase the DB performance in terms of response times, and whatsoever according to performance ?
View 8 Replies
View Related
Mar 27, 2013
I am working on an assignement where client is using Oracle 10g but stuck to using RBO Now the application team, from the GUI available to them build dynamic queries and some of them run very slow.
Neither the code can not be changed to tune the queries nor do we get the exact step in the plan which is an issue (being RBO).For some long running queries the Tuning advisor is not producing any recommendations.
Another hurdle is that all the application users are using same application user id so we can not write a logon trigger to use CBO for some particular queries to see what is happening in the background!
View 11 Replies
View Related
Jul 4, 2012
I want to tuning the next sql sentence. In this sql I want to get the hash_value and sql_text of the sentences that it's causing TX blocks. Is it possible?. This sentence works fine but sometimes It's slow.
SELECT DISTINCT hash_value,
sql_text
FROM gv$sql sq
WHERE hash_value IN (SELECT DISTINCT prev_hash_value
FROM gv$session se
WHERE sid IN (SELECT sid
FROM gv$lock l
WHERE type = 'TX'
AND ctime >= 2000
AND l.inst_id = se.inst_id
AND l.sid = se.sid)
AND sq.inst_id = se.inst_id);
[code]....
View 7 Replies
View Related
Nov 2, 2012
I see one of my SQL's which is ran by the user on a 10.2.0.3 database changing its SQL_ID after some runs even if the query is not changed a bit! However the HASH VALUE for this query remains the same.
how a same query can have different SQL_ID's but same HASH_VALUE?
Note: Statistics are not modified on the base tables of this query.
View 10 Replies
View Related
Aug 10, 2011
I am running Oracle 10.2.0.1.0 on MS Windows 2003 server 64-bit with 16G RAM.
Here is the findings for my Oracle database.
SQL> select * * from v$sgainfo;
NAME BYTES RES
-------------------------------- ---------- ---
Fixed SGA Size 1293560 No
Redo Buffers 7094272 No
Buffer Cache Size 830472192 Yes
[code]...
I find that the SGA component "Buffer Cache" is decreasing from the start "1.8G" and down to now 0.8G. On the other hand, the component "Shared Pool" is increasing from the start 0.3G to now 1.2G. I noticed that there are 100 operations of shrinking of "Buffer cache" and growth of "Shared Pool" in Oracle every day.Is it a indicator that I should raise up the SGA_MAX_SIZE?
I tried to increase the SGA_MAX_SIZE to 4G. But I cannot start the Oracle afterward.Is it a limitation of MS Windows(OS) or Oracle?I set the SGA_MAX_SIZE to 3G. This time, I can startup Oracle.What is the optimum/maximum I can set to SGA_MAX_SIZE?Is there any adverse effect/concern when setting the SGA_MAX_SIZE more than 2G?
View 6 Replies
View Related
Jul 11, 2012
Here i have three tier application. I want to know it host name from sid or sqlid . I want to know which query run on which host. Because i have one user from application to database. So i want to know which query consume more time on which host ?
View 19 Replies
View Related
Mar 17, 2006
How can I disable redo generation for DML statements.
View 25 Replies
View Related
Jul 26, 2011
I am getting enq: TS - contention as top event in AWR Report.where can i look into database to fix this issue.
View 14 Replies
View Related
Aug 14, 2010
I want to run some OLTP benchmarks on my system. I have looked up the TPC-E benchmarking suite .. but the documentation on the site makes no sense to me .
View 1 Replies
View Related
May 20, 2010
My DB is oracle10g.
I have AWR report comparison for two different days. I want to find the below things.
1. Which day has better performance?
2. What are the top two findings on the report.
I attached the report.
Here are my answer. Please correct me if i am wrong.
1. Which day has better performance? Second day has higher load. Since redosize is showing very high.
2. What are the top two findings on the report.
a) Compared to two days, first day, little bit more I/0 wait for single block read.
b) Compared to two days, 2nd day, it takes higher CPU.
However, which day is best compared to two days?
View 5 Replies
View Related
Jul 12, 2013
I have installed database in one server. I would like to enable AWR into it. Statistics_level is set to Typical. While running the below script to enable the AWR, its gives error -
SQL> exec dbms_scheduler.enable('GATHER_STATS_JOBS');
BEGIN dbms_scheduler.enable('GATHER_STATS_JOBS'); END;
*
ERROR at line 1:
ORA-27476: "SYS.GATHER_STATS_JOBS" does not exist
ORA-06512: at "SYS.DBMS_ISCHED", line 4343
ORA-06512: at "SYS.DBMS_SCHEDULER", line 2802
ORA-06512: at line 1
make AWR automatical generation.
View 3 Replies
View Related
Aug 31, 2010
In my awr reports I have CPU time(in seconds) as one of top 5 timed events.Does that mean oracle is waiting for my cpu to execute the statements.But my cpu usage is 0-10% always
View 4 Replies
View Related
