2. What are the general settings we need to adapt in a good performing BW system?
 
Following are the main parameters we need to monitor and maintain for a BW system. To start with performance tuning in a BW system, we have to focus on the following parameters.  Rsdb/esm/buffersize_kb.
Rsdb/esm/max_objects.
Rtbb/max_tables.
Rtbb/buffer_length.
Rdisp/max_wprun_time 
Gw/cpic_timeout
Gw/max_conn                    
Gw/max_overflow_size      
Rdisp/max_comm_entries
Dbs/ora/array_buf_size 
Icm/host_name_full 
Icm/keep_alive_timeout
 Depending on the size of the main memory, the program buffer should be between 200 and 400 MB. Unlike in R/3 Systems, a higher number of program buffer swaps is less important in BW Systems and is often unavoidable since the information stored in the program buffer is significantly less likely to be reused.  While the response times of R/3 transactions is only around several hundred milliseconds, the response times of BW queries takes seconds. However, by tuning the program buffer, you can only improve the performance by milliseconds.

Therefore, if the available main memory is limited, you should increase the size of the extended memory. However, the program buffer should not be set lower than 200 MB. If the available main memory is sufficient, the program buffer in BW 2.X/3.X systems should be set to at least 300 MB.

 BW users require significantly more extended memory than R/3 users. The size of the extended memory is related to the available main memory but should not be lower than 512 MB.
 
Set the Maximum work process runtime parameter to maximum and also set the timeout sessions to be high. Set the parameter dbs/ora/array_buf_size to a sufficiently large size to keep the number of array inserts, for example, when you upload data or during the rollup, as low as possible. This improves the performance during insert operations.
 The main performance-related tables in the BW environment are: 

• F-Fact tables: /BI0/F 
• E-Fact tables: /BI0/E
• Dimension tables: /BI0/D
• SID tables: /BI0/S
• SID tables (navigation attribute, time-independent): /BI0/X
• SID tables (navigation attribute, time-dependent): /BI0/YIn addition to the /BI0 tables delivered by SAP, you also have customer-specific /BIC tables with a naming convention that is otherwise identical.
  Since objects and partitions are frequently created and deleted in BW, and extents are thus allocated and reallocated, you should use Locally Managed Table spaces (LMTS) in the BW environment wherever possible.
  Since numerous hashes, bitmap and sort operations are carried out in the BW environment especially; you must pay particular attention to the configuration of the PGA and PSAPTEMP table spaces. These components are crucial factors in the performance of processing the operations described. You must therefore ensure that PGA_AGGREGATE_TARGET is set to a reasonable size and that PSAPTEMP is in a high-speed disk area. It may be useful to add up to 40 % of the memories available for Oracle to the PGA.
  If you work with large hierarchies, you have to increase the size of this buffer considerably. You should be able to store at least 5,000 objects in the buffer.
  The BW basis parameters must be set optimally for the BW system to work without errors and the system to perform. efficiently.  The recommendations for BW systems are not always the same as those for R/3 systems.