Performance Tuning :: How To Control Concurrent Inserts Of Record By Parallel Sessions
Aug 7, 2012
There is a detail table
There is a summary table
During batch process record is entered in detail table as well as summary table.
The process first checks if record exists in summary table for same group_no and if 'yes' then "updates" the record with the newly added amount (sums it) else inserts a new record
Whereas in the detail table it inserts the record directly
Now if the batch process runs in parallel, (out of many) two different sessions insert same group_no; This is because while sesond session inserts a record, first session inserting the same record (group_no) has not yet committed ; So second session Not knowing that already there is same Group_no (101) inserted, again inserts another record with same group_no rather than summing it.
Can it be solved without using temp table, select for update?
If we have not set parallel degree for a table then we can ( try to ) force parallel execution on a table using a parallel hint Does this 'parallelism' works on the index search in the query as well?
In which situations non-parallel non-partitioned table but parallel index (degree>2) will facilitate a query?
I want to load 10 millions records from staging table to master table.One logic must be take during the load, the logic is rows already present in master table means, we need to update corresponding rows in master table otherwise rows insert in target table.
I have been using bulk collect and forall method to load data. it shows better performance compare then cursor row by row process. As per oracle doucmentation, we cannot use SELECT statements inside FORALL condition so we could not use logic inside the forall condition.
how to avoid oracle deadlock with two sessions. Here is my example, We use Select query with For Update in order to get the unique number from a table. When one user has accessed this query, while the other user tries, System gives a Performace slow and when checked it is due to locking of this select query with For update.
We don't want to use For update WAIT or FOR UPDATE NOWAIT since these will result in missing of number.
The TM lock that occurred 3 times appears to be disastrous.Historically, this could be caused by missing indexes on foreign key columns.
How can I be alerted when this event occurs, so that I can do some real-time investigation into the sessions and the SQL that hit it? I suppose I could schedule a job to query v$lock/dba_waiters/dba_blockers every few minutes, but is there a better way? Any standard edition scripts for this?
I am inserting data into a global temporary table and then using 'parallel' hint to query from this temporary table. I remember reading that the queries on the temp table may not run in parallel as the parallel sessions may not be able to see the data in the temporary table
However the execution plan as well as px_session, v$sql indicate that the query on the temporary table in fact run in parallel mode
select * from table(dbms_xplan.display_cursor(null,null,'ALLSTATS LAST'));
PLAN_TABLE_OUTPUT ----------------------------------------------------------------------------------------------------------------------- SQL_ID 7d68g52g0mskz, child number 0 ------------------------------------- select /*+ gather_plan_statistics parallel(t,4) */ * from dbo_gtt t order by id,object_id
I am trying to execute two scripts at the same time (concurrent) in Oracle SQL Developer. I know we can schedule a job using DBMS_job package and define the job. But is there any other way of doing it using Threads ?
We are experiencing a problem with SSO causing 2nd or 3rd concurrent Oracle sessions to hang. The Oracle application hangs during loading and the task manager has to be used to close the application.
I have tested logging onto our application servers using SSO and I cannot load more than 3 concurrent Oracle sessions. When I bypass the SSO and logon to the same server I can load more than 20.
I am executing a sql statement which is doing FTS in parallel mode The server has 8 cpus and threads_per_cpu is 2
The v$sql shows PX_SERVERS_EXECUTIONS as 8
select PX_SERVERS_EXECUTIONS, sql_text from v$sql where sql_id='0q0nk5117yth2' 8, select /*+ full(a) parallel(a)....
however the px_sessions shows 17 sessions (16 parallel session + 1 parent session (where sid = qcsid) Now in px_sessions, these 16 parallel session are divided in 2 server sets 1 and 2 and values for degree and required degree are 8 and 16 respectively
However, all the time, only 8 sessions which belong to server set = 1, were active though its state was waiting with event "PX Deq Credit: send blkd"
The other session which belong to server set = 2 were never active and always had waint event ='PX Deq: Execution Msg'
what could be the reason that 16 parallel session could not be started though I am the only person using the server, there aren't any batch jobs, dbms_jobs,even archivelogs (not a prod system)?
Note that paralel_max_servers setting is 16
Another issue being the duing start of the query approximately 100-115 blocks were read for the query (checked from longops) however after 60-70% blocks are read the number of blocks read / seconds falls down to 10-20 blocks / second across all parallel sessions.
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.
I have prepared shell scripts to do the parallel inserts on my DB table (LEGACY_SYSTEM).
There is a trigger (AFTER INSERT ON EACH ROW) associated with the above table. I am calling a package.function inside the trigger to do the required operation and finally it will insert records into my target table (PRICE_CHANGE).
Expectation: ------------ If I insert 10 rows into LEGACY_SYSTEM table, it should do few updates and finally insert 10 rows into PRICE_CHANGE table.
Result: ------- 10 rows got inserted into LEGACY_SYSTEM. All the updates are successful but I could see only 4 rows in PRICE_CHANGE table. If I run it for the second or third time, all the results will be perfect.
Instead of these shell script, if I insert one by one rows manually into LEGACY_SYSTEM table, I am getting all the expected results and the results are consistent. If you look at my scripts below, you will understand the problem better..
I am calling test_global.sh through the UNIX session and all the records got inserted into LEGACY_SYSTEM table and few rows are missing from PRICE_CHANGE table.
If I remove the '&' symbol and execute, the results are perfect. But the requirement is not to remove the '&' symbol. I have been facing this problem for the past 1 month.
select serialnumber from product where productid in (select /*+ full parallel(producttask 16) */productid from producttask where startedtimestamp > to_date('2013-07-04 00:00:00', 'YYYY-MM-DD HH24:MI:SS') and startedtimestamp < to_date('2013-07-05 00:00:00', 'YYYY-MM-DD HH24:MI:SS') and producttasktypeid in
I need to identify, whether my current session is one of slave sessions scheduled as Oracle scheduler job via DBMS_PARALLEL_EXECUTE or not. I already succeeded using join of dba_scheduler_running_jobs, user_parallel_execute_chunks and v$session, but I feel that this is not optimal approach.
At my prod instance one sql query ran for about 9 hours.Now the sql query completed with success.Suddenly our ops team want to know the which sql query was running for 9 hours.As the query got success no record is being found at session level.
We have a database that is accessed by ArcSDE, a product to modify maps. It uses BLOBs to store those maps.
We ran a load on the server and the response time was slow. By running the following query:
select event, total_waits, time_waited, avg_ms, round(ratio_to_report(time_waited) over () * 100) percent from (select substr(event, 1, 30) event, total_waits, time_waited, round(time_waited_micro / total_waits / 1000, 2) avg_ms from v$system_event where wait_class in ('System I/O') union select 'CPU' event, NULL, value, NULL from v$sysstat where statistic# = 12 order by 3 desc) where rownum <= 10;
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?
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,
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'.
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?
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 ?
In my form line level block contains 100 records.i will check the check box for line number 96 and 97. Then i will press save(I have written some logic here) button it will generate one number for selected check boxes. After generating this number cursor(control) should be on same line number 96 or 97.
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?
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?
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.
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.
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.
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'
