Chapter 20 Other Memory Management Topics

Overview Memory management in Oracle Result Cache Oracle 10G: ASMM (Dynamic SGA) Oracle 11G: AMM (Dynamic SGA & PGA) Result Cache Optimization of other memory areas Shared Pool Large Pool Redo Buffer

Optimizing Overall Memory AMM (Automatic Memory Management) Oracle 11G feature Let’s Oracle decide how to allocate between pools Includes between SGA components and PGA ASMM (Automatic Shared Memory Management) Oracle 10g feature Let’s Oracle decide how to allocate for SGA only PGA still separate entity managed on it’s own

IO Wait Times / Memory Optimization Memory optimization helps reduce IO Categories of Oracle IO include: Buffered datafile IO Temporary segment IO waits Direct path reads System IO See “Active Sessions Waiting” chart in OEM

Using Advisories For PGA In Oracle 11g In Oracle 10g Look at V$PGA_TARGET_ADVICE Includes elapsed times Compare directly with V$DB_CACHE_ADVICE In Oracle 10g Need to calculate elapsed times outside of V$PGA_TARGET_ADVICE Determine average time and block counts Use averages to convert byte counts Combine times with buffer cache advisory

AMM Enable by setting parameters Optionally set (minimum sizes for) MEMORY_MAX_TARGET MEMORY_TARGET Optionally set (minimum sizes for) SGA_TARGET PGA_AGGREGATE_TARGET Individual pool parameters, such as LARGE_POOL Can also configure in OEM Go to Advisor Central Then to Memory Advisors

AMM (cont.) Monitoring Memory Allocations Views show useful statistics Can monitor using several dynamic views V$MEMORY_DYNAMIC_COMPONENTS V$MEMORY_RESIZE_OPS V$MEMORY_TARGET_ADVICE Views show useful statistics Current memory allocations Minimum and maximum sizes Details on each resize operation Affect on performance for potential resize operations

AMM Issues & Considerations Set minimum sizes for memory components Helps avoid memory “thrashing” Helps avoid “memory starvation” Not all memory components are part of AMM Nondefault buffer pools AMM incompatible with “Linux HugePages” Cannot lock SGA when using AMM (LOCK_SGA)

Result Set Cache Entire result sets stored in shared memory Can help avoid Parse time Logical reads Physical reads Cache contention (e.g. latches) Effective only in certain scenarios Read only or nearly read only data Small result sets Needs to be used sparingly to avoid result cache latch contention Expensive queries that meet above criteria Can store PL/SQL Functions in cache in certain situations

Configuring the Result Cache Set with parameters RESULT_CACHE_MODE={OFF|MANUAL|FORCE} RESULE_CACHE_MAX_SIZE (size of cache) RESULT_CACHE_MAX_RESULT (maximum size of one result) Monitor with V$RESULT_CACHE_STATISTICS Monitor contention by looking for “latch free” waits Use with caution: RESULT_CACHE_MODE=FORCE The RESULT_CACHE table property

Other Memory Optimizations Sizing the Shared Pool Moderately sized pool generally sufficient See V$SHARED_POOL_ADVICE for help Using bind variables important for efficiency If not used, size increases usually not helpful Review setting of CURSOR_SHARING parameter Large Pool Sizing Optional SGA component Reduces shared pool fragmentation Used for shared server configuraton Used for parallel processes Redo Log Buffer is generally small and self sufficient Locking the SGA in memory helpful in certain scenarios