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3132530 - Transaction log in data cache - SAP ASE 16.0

Symptom

  • Looking for recommendations for creating/using dedicated log data cashes in ASE 16.0.
  • The "TUNING DATA CACHE IN ASE 15" presentation (see https://docplayer.net/60756431-Tuning-data-cache-in-ase-15-dial-numbers-passcode-sybase.html) has the following slide:
     
       The Need for a Dedicated Log Cache  

    • Log semaphore is a lock on the last log page

      • Therefore it moves as the log is appended to.
      • Logical lock ‐ not a spinlock 

    • Log pages in a shared data cache

      • Log appends cause contention with cache semaphore for other cache changes
      • Cache partitioning “scatters” contiguous log allocations among partitions meaning log scans such as checkpoints, database triggers, etc. have to potentially grab multiple spinlocks during processing
      • Log appends can lead to pushing data pages out of cache

    • Other optimization considerations

      • The HK Wash does not run in a log ‐ only cache....therefore by having log pages in a mixed cache, the HK Wash runs unnecessarily against log pages
      • Checkpoint process will do physical reads from log and physical writes to data (it does not do physical reads from data pages)


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Environment

SAP Adaptive Server Enterprise (SAP) 16.0 SP03 

Product

SAP Adaptive Server Enterprise 16.0

Keywords

"user log cache size", user, size, ULC, session, tempdb, "user log cache queue size", "user log cache spinlock ratio, "session tempdb log cache size", , KBA , BC-SYB-ASE , Sybase ASE Database Platform (non Business Suite) , How To

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