Standard Value to set SGA and PGA Memory in Oracle

Setting the appropriate values for SGA (System Global Area) and PGA (Program Global Area) is crucial for optimizing Oracle database performance. If you have 64 GB of total memory available on your server, you need to allocate memory to SGA and PGA wisely to balance between database cache, session management, and overall performance. Below are some guidelines for setting SGA and PGA values:

Recommended Allocation Strategy

For a server with 64 GB of total memory, consider the following strategy:

  1. SGA and PGA Distribution:
    • Typically, allocate about 60-70% of the total memory to Oracle, leaving some for the OS and other processes.
    • For example, if using 60% of 64 GB, then about 38 GB can be allocated to Oracle memory (SGA + PGA).
  2. SGA and PGA Breakdown:
    • SGA (System Global Area): Allocate about 75-80% of Oracle's allocated memory.
    • PGA (Program Global Area): Allocate about 20-25% of Oracle's allocated memory.

Memory Settings Calculation Example:

  • Total Memory for Oracle: 60% of 64 GB = 38 GB (approximately).
  • SGA Size: 75% of 38 GB ≈ 28.5 GB.
  • PGA Size: 25% of 38 GB ≈ 9.5 GB.

Suggested Parameter Values:

  1. SGA Settings:


    ALTER SYSTEM SET sga_target = 28G SCOPE = BOTH;
ALTER SYSTEM SET sga_max_size = 28G SCOPE = SPFILE;

  2. PGA Settings:


    ALTER SYSTEM SET pga_aggregate_target = 9G SCOPE = BOTH;
ALTER SYSTEM SET pga_aggregate_limit = 12G SCOPE = SPFILE;  -- Optional, to cap PGA memory usage

Considerations:

  • OS Memory Requirements: Ensure that about 30-40% of the memory is left for the operating system and other processes, i.e., at least 18-26 GB.
  • Adjust Based on Workload: These values are starting points. You may need to fine-tune based on database workload, session count, and performance observations.
  • Monitor Memory Usage: Use Oracle’s AWR (Automatic Workload Repository) reports and views like v$sga_target_advice and v$pga_target_advice to monitor memory usage and adjust as needed.

Key Points:

  • SGA is used for shared memory structures, including the buffer cache, shared pool, and redo log buffer.
  • PGA is used for session-specific memory, sorting, and hash joins, important for complex queries and OLAP operations.

Properly setting and managing SGA and PGA helps ensure that your Oracle database performs efficiently, avoiding memory shortages or over-allocations that can impact system stability and performance.






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