SQL - degree Maximum parallelism

Similar Questions

• Degree of parallelism

  Hello

  I like to read Oracle Performance Tuning Guide (11g R2, Chapter 11)

  When I was reading on fulltable scan it says that

  High degree of parallelism

  A high degree of parallelism for a table tilts the optimizer to full table scan on the beaches of analyses. Look at the column LEVEL in ALL_TABLES for the table to determine the degree of parallelism

  
  I did not understand this. When I questioned all_tables I see only the value 1 in the LEVEL column. Can you explain what values will be there in the level column and how it will force Full Table Scan.

  Thanks a lot for your help in advance.

  See you soon,.

  Suri

  SQL > create table tbl (number)
  2.

  Table created.

  SQL > select degree
  user_tables 2
  3 where table_name = 'TBL '.
  4.

  DEGREE
  ----------
  1

  SQL > drop table tbl purge
  2.

  Deleted table.

  SQL > create table tbl (number)
  4 parallel 2
  3.

  Table created.

  SQL > select degree
  user_tables 2
  3 where table_name = 'TBL '.
  4.

  DEGREE
  ----------
  4

  SQL >

  SY.

• run statistics with a degree of parallelism

  Hello
  
  I want syntax to collect statistics of database with the degree of parallelism...
  
  Please tell me

  You can simply check out the documentation:
  http://docs.Oracle.com/CD/E11882_01/AppDev.112/e25788/d_stats.htm#i1036461

  DBMS_STATS.gather_table_stats (..., degree-online x...);
  Same thing with gather_database_stats etc.

• degree of parallelism and the number of files in the tablespace

  Hello
  
  I'm trying to find the relationship between the number of files in a tablespace and the degree of parallelism. because of the number of files in a tablespace effect dop in parallel query. because if several files are in the tablespace/o of the system has increased and the system became more feverable for a query parallel.
  
  But I looked in the dop formulas I can't find any settings that specify how the file is there in a tablespace. Please give me the formula for calculting dop in oracle.
  
  
  concerning
  Nick

  Hi Nick,

  It is not easy to determine the optimum degree of parallelism for the tasks of the Oracle.

  Oracle says that the best degree of parallelism for a query is based on several factors. These factors are presented in order of importance:

  -The number of processors on the server.

  -The number of physical disks located in the tables.

  -For parallelization of the partition, the number of partitions that will be available, based on the size of partition (if any).

  I can't find any settings that specify how the file is there in a tablespace.

  This is the number of physical spindles that matters, is not at the level of the tablespace.

  If I have diploma = 8, cpu_count = 8 and data are on 8 discs, there is no pretense.

  It's one of the problems with big great drives today, too few concurrency...

  I hope this helps...

  Donald K. Burleson
  Oracle Press author
  Author of "Oracle Tuning: the definitive reference".
  http://www.rampant-books.com/book_2005_1_awr_proactive_tuning.htm

• Is it possible to set the degree of parallel on Auto?

  Is it possible to adjust the degree of the parallel to Auto in the physical model?
  I can see to turn on the parallel and can set the degree of a number, I am just unable to know how the Auto value.
  
  Thank you
  NIC

  Hi Nic,

  By Auto, I assume you mean DOF consisting of PARALLEL on its own, rather than whole PARALLEL.

  It is generated if you set the parallel property to YES and leave blank the level property.

  David

• scheduled to run every day 'Index close to degrees' maximum but failure due to

  We planned to run 'Indexes close to maximum degrees' every day and there was a mistake by running on a given date.
  
  It fails to run and reported by the following in the log file:
  usdsop has encountered an error creating a new process. [Reason]. Action:
  Check that your system has sufficient resources to start a new process.
  
  Can I know the possible cause and repair/prevention?
  
  Kind regards.

  Salvation;

  What is your version of EBS - OS? You have enough resources on your system? (Swap-ram, etc)

  Please check below notes which is consult similar error like yours

  Output Post processor (OPP) fails with oracle.apps.fnd.cp.gsm.GenCartCommException: ORA-01403 error after application 11I. ATG_PF. H.DELTA.7 - 6241631 [1066869.1 ID]
  CMCTCM - Cost Manager Error - USDSOP could not create a new process [1084030.6 ID]
  The Adadmin and utility Adpatch fails, Usdsop cannot create a new process on Windows platform [ID 123635.1]

  Respect of
  HELIOS

• TestStand SQL reuest maximum of a column

  
  

  Hello James,

  Thank you very much for the reply.

  I tried your suggestion, it's but unfortunatelly Teststand gives an error because it cannot properly manage the locals.max in the query.

  But I tried others maybe your idea of using the key word "Sub":

  First of all, I use:

  The Open statement: SELECT MAX (myTAB.Col1) as myTAB MAXI

  I don't know how teststand handles the "variable" MAXI.

  But when I then add step

  Action SQL: Get - retrieve the values of recording with as column/parameter values:

  Name/number: "MAXI".

  Values: Locals.Max

  It works properly

  Thank you very much

  Ham

• Degree of parallelism 0 or 1

  Hello

  Some said documentatiins that DOP = 1 means, others noparallel said DOP = 0 means noparallem...

  SO, what's the right answer?

  Thanks in advance.

  Degree = 0 is set to index LOB which are kept internally by database and cannot be changed.

• How to define a pl/sql function deterministic, parallel to OWB 11.2?

  Hello
  
  on my site of the client, we start with the new development work after upgrade from 10.2 11.2 OWB and we do not find the configuration parameter to define a function deterministic and parallel within a new package. The 'old' 10.2 function dialog box had a few checkboxes for these two features...
  
  Thanks in advance
  
  Michael

  If you create service outside package and configure as deterministic parallel and then CUT and PASTE in the package, it will keep all its properties you can see when you generate the code.

• Dangers of parallel (degree n) at the level of the table

  What all things I would be informed when PARALLEL (degree n) was implemented on a very large table to (especially) faster SQLs.
  
  I know, it can drive up to CPU & i/o etc... I'm looking for is, how the optimizer react to this settings... What path this setting would make unavailable or unfavourable etc etc...
  
  Thanks in advance...

  user4529833 wrote:
  Thank you everyone. Jonathan, very good section on size measure PQ and AUTO.  I saw these DL readings several times and always wondered why, but now I know why. So solution here to avoid this option to use the uniform extensions. Right?

  OK - and then you have to choose the size of your measurement carefully to avoid excessive production of waste of space (as mentioned by Bert Scalzo).

  On average, if you make a parallel ETG or insert as Select, each slave will end up with half a measure of free space in her last litter. If you are likely to get the waste of space of approximately (degree of parallelism * extent_size / 2) altogether.

  If you choose a very large measure, or a very high degree of parallelism, this could lead to a lot of waste of space in the object. As I indicated above, however, I haven't checked this recently, so there may be some improvements to reduce waste in algorithms that use Oracle.

  Concerning
  Jonathan Lewis
  http://jonathanlewis.WordPress.com
  http://www.jlcomp.demon.co.UK

  "Science is more than a body of knowledge; It's a way of thinking"Carl Sagan

• Feature of the parallel execution of SQL query

  Hello guys,.

  I installed a 11 GR 2 Oracle RAC (11.2.0.3) database, but I see the use of the feature of running parallel SQL queries, but I never used that.

  I would like to know if this feature is enabled by default on CCR environments and if it does not require me to pay for Enterprise Edition.

  NAME DETECTED_USAGES FIRST_USA LAST_USAG CURRE

  ---------------------------------------------------------------- --------------- ----- --------- ---------

  Checking Options 1 TRUE 9 October 15 October 9, 15

  BMG Auto setting 1 TRUE 9 October 15 October 9, 15

  Memory of the execution of SQL auto 1 TRUE 9 October 15 October 9, 15

  Automatic management of the space Segment (System) 1 TRUE 9 October 15 October 9, 15

  Automatic Storage Management 1 TRUE 9 October 15 October 9, 15

  Management of the Undo Automatic 1 TRUE 9 October 15 October 9, 15

  Character set 1 TRUE 9 October 15 October 9, 15

  Deferred Segment creation 1 TRUE 9 October 15 October 9, 15

  Locally managed tablespaces (System) 1 TRUE 9 October 15 October 9, 15

  Locally managed tablespaces (user) 1 TRUE 9 October 15 October 9, 15

  Logfile multiplexing 1 TRUE 9 October 15 October 9, 15

  Oracle Java Virtual Machine (System) 1 TRUE 9 October 15 October 9, 15

  Oracle utility of metadata API 1 TRUE 9 October 15 October 9, 15

  1 SQL query in parallel TRUE 9 October 15 October 9, 15

  Partitioning (System) 1 TRUE 9 October 15 October 9, 15

  Real Application Clusters (RAC) 1 TRUE 9 October 15 October 9, 15

  Recovery zone 1 TRUE 9 October 15 October 9, 15

  SECUREFICHIERS (System) 1 TRUE 9 October 15 October 9, 15

  SECUREFICHIERS (user) 1 TRUE 9 October 15 October 9, 15

  The parameter server file 1 TRUE 9 October 15 October 9, 15

  Thanks in advance,

  Franky

  You are not, but Oracle is, since you are using RAC.  Oracle relies on execution in parallel against the gv$ views so even if you can't use it in SE way common Oracle can when it comes to query against one of the points of view gv$.  That's why DBA_FEATURE_USAGE_STATISTICS reports that you see.

  David Fitzjarrell

• Parallel degree importing Datapump

  Hello

  For several imports that I ran, I observed a constant degree of parallelism = 10 when creating index.

  Moreover, I parallel_degree_limit = en parallel_degree_policy = MANUAL CPU.

  The first parameter specifies that Oracle sets up to an upper limit on the DOP.

  If this explains the value observed?

  Kind regards

  Hello

  At the same time goes like this:

  all the tables, plsql definitions are created in series

  All data in the table of loading in parallel - so not parallel insertion into a table but a work process separate datapump by table - so EMP would be charged by slave1 and DEPT by slave2 - but at the same time. IN your case 10 separate tables would all be imported at the same time.

  The indexes are built at the same time you specify

  Constraints are made in series one and the same process, I think

  I wrote a short blog about it earlier that can be useful: it contains pictures! :-)

  Oracle DBA Blog 2.0: What happens during an import parallel datapump?

  See you soon,.

  Rich

• Degree parallel data pump

  Hello
  
  I have an impdp job running a long time and I think it's maybe due to too high degree of parallelism. Currently it takes about a minute for a connection session to create.
  
  Is there a way to reduce this number in the middle of an import? I see the degree DBA_DATAPUMP_JOBS and the corresponding sessions. Can I update this table Data Pump to reduce the number of sessions created by Data Pump? What comes to mind is by updating the column of DEGREE, but it seems risky.
  
  On a related topic, Hat are general rules to decide on a number of parallel processes?
  
  It's about Oracle 11.2.0.3.
  
  Thank you and best regards.

  I see the degree DBA_DATAPUMP_JOBS and the corresponding sessions. Can I update this table Data Pump to reduce the number of sessions created by Data Pump? What comes to mind is by updating the column of DEGREE, but it seems risky.

  You shouldn't be updated any table data pump.
  You can use the command line interface and connect to the session of import do the work.

  Impdp-help (see the bottom section)
  The following commands are valid in interactive mode. Note: the abbreviations are allowed.
  PARALLEL: Change the number of active workers for work in progress.

  I have not done, but it seems that the PARALLEL parameter can help you.

• How to know the degree of optimal parallelism for my database?

  I have an important application on my (Oracle 10,2,0) databae and the box has 4 CPU. All tables are not partitioned. Should I set the parallel degree by myself?
  
  How to know the degree of optimal parallelism for my database?

  As far as I am concerned there is no optimum degree of parallelism at the database level. The optimal value depends on the query based on the plan in use. This may change over time.

  It is not so difficult to abuse of the PQO and end up harming the overall database performance. PQO is a brute force methodology and should be applied with caution. Otherwise, you end up with results inconsisten.

  You can let Oracle manage, or you can manage it on the level of education through advice. I do not have to specify the degrees of parallelism to the object level. As I said, no two queries are exactly alike and what is right for a query on a table cannot be good for another query on the table.

  In the case of doubt put in place the system to let Oracle manage. If you ask really, it's how many sessions to allocate PQO then look at your reports Statspack or AWR and judge your system load. Monitor v$ px_session and v$ pq_slave to see how these views show activity.

  IMHO - Mark D Powell-

• Running parallel queries in 11 GR 2

  I'm a little confused about parallel execution in GR 11, 2.

  Lets say I have the Setup below.

  parallel_servers_target = 4;

  PARALLEL_MAX_SERVERS = 16;

  parallel_degree_limit = CPU

  parallel_threads_per_cpu = 2

  parallel_adaptive_multi_user = TRUE

  N ° of UC = 16 CPU, 2 cores each.

  The Test table degree = DEFAULT

  Example query:

  Select * from Test by 1,2,3;

  Lets say I want to run 5 in parallel sql statements that require 4 parallel workers each.

  PARALLEL_DEGREE_POLICY = AUTO:

  What of her below happen?

  (a) a statement was going to be executed and the rest four would be queued because the first statement itself uses 4 parllel workers what amounts to our parameter of parallel_servers_target.

  or

  (b) four statements would be carried out using 4 workers each and the fifth would be queued because it exceeds the parallel_max_servers setting if it were to be executed.

  or

  Please explain what could happen if not a) or b).

  PARALLEL_DEGREE_POLICY = MANUAL:

  What of her below happen?

  (a) four statements would be managed (using 4 parallel slaves each) and the fifth will be held in the series.

  or

  (b) all five would be using parallel workers. If so, please explain how the No. parallel to each statement slaves were to be distributed.

  or

  (c) it would first try to allocate 16 sons in the first statement. Later it will adjust accordingly and reduce parallel workers allocated to each statement and end up running two 4 statements with parallel workers or all the five workers parallel.

  I appreciate really all of your answers on this.

  UC = 60 (perhaps CPU_COUNT = 60), the number of cores = 15 - so you have four hardware threads by heart.

  The DOP default value is calculated as PARALLEL_THREADS_PER_CPU * CPU_COUNT (in the single instance databases) - in your case, the DOP default is 2 * 60 = 120.

  See this page 20 (http://www.oracle.com/technetwork/database/bi-datawarehousing/twp-parallel-execution-fundamentals-133639.pdf) :

  Manually set the degree of parallelism

  With PARALLEL_DEGREE_POLICY set to MANUAL Auto DOP feature is disabled and the end user must manage the use of parallel execution in the system.

  You can either apply the default value of the so-called DOP or a specific fixed value for the declaration of principles on a session, statement or object level.

  LACK of parallelism

  ...

  Fixed degree of parallelism (DOP)

  Unlike the LACK of parallelism, a specific DOP can be asked to the Oracle database. You can use one of the following ways to get a fixed DOP.

  1. define a fixed DOP for objects. ALTER TABLE 8 PARALLELS customers. ALTER TABLE 16 PARALLELS sales;

  2. use the suspicion level parallel (integer) statement. SELECT / * + parallel (8) * / COUNT (*) OF customers.

  3. use the level indicator parallel (table_name, whole) object. SELECT / * + parallel (8 customers) * / COUNT (*) OF customers.

  Note that the parameters in the table on the #1 above give you only the fixed DOP in manual mode and mode limited, namely when PARALLEL_DEGREE_POLICY is set to MANUAL or LIMITED.

  All table decoration will be ignored in mode (AUTO or ADAPTIVE) AutoDOP.

  Also note that for example # 1 parameters, Oracle will choose the DOP requested as follows:

  -The queries accessing the CUSTOMERS table use a DOP asked 8.

  -Accessing the SALES table queries ask a DOP of 16.

  -Queries accessing both the SALES and the CUSTOMERS table will be processed with a DOP of 16. Oracle uses the upper DOP2.

  The number of allocated PX servers can become always twice the requested DOP in the case of parallel processing requires two sets of PX server for treatment of producer/consumer.

  And see on page 25:

  Parameter: PARALLEL_MAX_SERVERS

  Default value: PARALLEL_THREADS_PER_CPU * CPU_COUNT * concurrent_parallel_users * 5

  Suggested value: default

  Explanations: Sets the maximum number of servers in parallel execution that can allocate an instance of database. This is a hard limit and cannot be exceeded.

  So, put PARALLEL_MAX_SERVERS > 120.

  In fact, it would be better to change the PARALLEL_THREADS_PER_CPU = 1 parameter (default is 2). See this page 25:

  Parameter: PARALLEL_THREADS_ PER_CPU

  Default value: 2

  Suggested value: 1 for platforms with hyperthreading enabled, 2 for other platforms

  Explanations: Number of parallel processes that a processor can handle in parallel execution

  Then the default DOP would be PARALLEL_THREADS_PER_CPU * CPU_COUNT = 1 * 60 = 60.

  In this case, set PARALLEL_MAX_SERVERS > 60.

  Kind regards

  Zlatko