Issues with parallel processing in Logical Database PCH and PNP

Question

Has anyone encountered issues when executing programs in parallel  that utilizes the logical database PCH or PNP?
Our scenario is the following:
We having have 55 concurrent jobs that execute a program that use the logical database PCH at a given time.  We load the the PCHINDEX table with the code below.
      wa_pchindex-plvar = '01'.
      wa_pchindex-otype = 'S'.
      wa_pchindex-objid_low = index_objid.
      APPEND wa_pchindex TO pchindex.
We have seen instances where when the program is executed in parallel, with each process having its own range of positions id's, that some positions are dropped or some are added that is outside the range of the given process.
For example:
process 1 has a range of positions ID's 1-10
process 2 has a range of positions ID's 11-20
process 3 has a range of positions ID's 21-30
Process 3 drops position 25 and adds position 46.
Has anyone faced a similar issue?
Thanks for your help.
Best Regards,
Duke

Answer 1

Hi,
first of all, you should read [Using Parallel Execution|http://download.oracle.com/docs/cd/B19306_01/server.102/b14223/usingpe.htm#DWHSG024] in documentation for your version - almost all of these topics are covered there.
1. According to my server specification how much DOP i can specify.It depends not only on number of CPU. More important factors are settings of PARALLEL_MAX_SERVERS and PARALLEL_ADAPTIVE_MULTI_USER.
2. Which option for Setting Parallel is good - Using the 'alter table A parallel 4' or passing the parallel hints in the sql statementsIt depends on your application. When setting PARALLEL on a table, all SQL dealing with that table would be considered for parallel execution. So if it is normal for your app to use parallel access to that table, it's OK. If you want to use PX on a limited set of SQL, then hints or session settings are more appropriate.
3. We have a batch processing jobs which are loading data into the tables from flat files (24*7) using sql loader. is it possible to parallel this operation and any negative effect if enabled parallel.Yes, refer to documentation.
4. Query or DML - which one will be perform best with parallel option.Both may take advantages of using PX (with some restrictions to Parallel DML) and both may run slower than non-PX versions.
5. What are the negative issue if parallel option is enabled.1) Object checkpoint happens before starting parallel FTS (true for >=10gR2, before that version tablespace checkpoint was used)
2) More CPU and memory resources are used with PX - it may be both benefit and an issue, especially with concurrent PX.
6. what are the things to be taken care while enabling the parallel option.Read the documentation - it contains almost all you need to know. Since you are using RAC, you sould not forget about method of PX slaves load balancing between nodes. If you are on 10g, refer to INSTANSE_GROUPS/PARALLEL_INSTANCE_GROUPS parameters, if you are using 11g then properly configure services.