About Me

My name is Stefan Koehler and i am a freelance consultant and the founder of Soocs.
I started my career with an "IT specialist / system integration" apprenticeship in 2001 and completed successfully 3 years later as one of the best in my year. Afterwards i worked as a classic *nix admin (primarily focusing on IBM AIX and Linux) and Oracle DBA for round about 2 years before i joined the SAP area with the main focus on Oracle databases and SAP performance tuning.
In 2011 i founded my own freelance company Soocs to provide independent and specialized consulting services for Oracle databases and SAP performance tuning in mission critical environments.

Since +13 years i follow my passion about Oracle and specialized in Oracle and SAP performance tuning, especially in Oracle cost based optimizer (CBO) and database internal related topics. I am not just interested into understanding how an Oracle database feature works, but also how it is implemented in detail. In consequence i research a lot of Oracle database internals for education purpose or on client’s needs. In addition Oracle High Availability and Oracle Backup and Recovery are completing my skill set.

Nowadays i primarily work as a freelance Oracle database performance consultant and SAP performance analyst in large mission critical environments (e.g. +10 TB databases or +4000 concurrent SAP users) for market-leading companies or multi-billion dollar enterprises in various industries all over the world. I usually support my clients in understanding / solving complex Oracle performance issues and troubleshooting nontrivial database issues on short-term contracting basis.

I constantly share my experiences, findings and knowledge with the Oracle and SAP community through my blog and my activity on Oracle-L, Oracle technology network, SAP community network and Twitter. Sharing knowledge is one of my key aspects when working with clients or interacting with the community. I am also one of the leading contributors on the SAP community network in the "SAP on Oracle" area and i received awards by SAP for being the #1 SCN Topic Leader (2012/2013) – SAP on Oracle and #2 SCN Topic Leader (2013/2014) – SAP on Oracle. In 2015 i received the greatest honor in my professional career as i was invited to join the well-known OakTable network, an informal organization of Oracle experts around the world, who believes in better ways of administering and developing Oracle based systems.
Stefan Koehler

Consulting services

I am your reliable partner for mission critical issues or “must not fail” projects and always up to go the extra mile with you. I keep the focus on your needs and issues without wasting time by playing political games. This level of expertise has never been so affordable, so flexible or so easy to acquire – just call me. All activities are provided under confidentiality agreements.

Oracle RDBMS

  • Performance analysis and tuning of Oracle databases
  • Performance analysis and tuning of SQL statements
  • Analysis and benchmarking of performance and scalability
  • Application design and instrumentation for Oracle databases
  • Troubleshooting of Oracle database issues (e.g. crashes)
  • Design and implementation of Oracle Data Guard solutions
  • Design and implementation of Oracle RAC solutions
  • Design and implementation of Oracle RMAN solutions

  • Operating system

  • AIX performance tuning as platform for Oracle or SAP
  • Linux performance tuning as platform for Oracle or SAP
  • Design of operating system architecture for Oracle or SAP
  • Implementation of HA infrastructure for Oracle or SAP
  • SAP on Oracle

  • Performance analysis and tuning of SAP systems
  • Performance analysis and tuning of SAP applications
  • Performance analysis and tuning of R3load based migrations
  • Analysis and benchmarking of performance and scalability
  • Near zero downtime OS/DB migrations based on advanced Oracle database technologies
  • Your advantages by using my services

  • Knowledge about Oracle cost based optimizer (CBO) internals
  • Knowledge about Oracle database core component internals
  • Active researching of Oracle database internals and operating system integration (e.g. DTrace, GDB, Perf, Procstack, etc.)
  • Specialized knowledge about Oracle for SAP systems
  • Live analysis or troubleshooting with your IT staff
  • Client-specific performance workshops (e.g. about cost based optimizer, troubleshooting, etc.)
  • Flexible booking and short-term availability in general
  • Standby and Go-Live support for cut-over activities

  • If you have any further questions about my services, please get in contact directly.


  • [Oracle] Trace back to responsible SQL or PL/SQL code for a particular (PGA) memory request by intercepting process with DTrace
  • [Oracle] Understanding the Oracle code instrumentation (wait interface) - A deep dive into what is really measured
  • [Oracle] Insights into SQL hints - Embedded global and local hints and how to use them
  • [Oracle] DB Optimizer Part XII - Revealing SQL Plan Directive details for existing/loaded cursor from CBO (and SQL Dynamic Sampling Services) trace
  • [Oracle] Researching internal latch implementation (ksl_get_shared_latch, kslfre, kslgetsl_w) and crashing PMON
  • [Oracle] SQL Execution Engine Part I - Join data by hashing alias Hash Joins
  • [Oracle] - New diagnostic event "wait_event[]" (and others) for troubleshooting / researching purpose with Oracle 12c
  • [Oracle] DB Optimizer Part XI - Query transformation fixes false cardinality estimation with multiple OR predicates (in newer Oracle releases)
  • [Oracle] Mess up CBO cardinality estimates by using DBMS_STATS.COPY_TABLE_STATS with one distinct value in first partition column
  • [Oracle] DB Optimizer Part X - Looking under the hood of Adaptive Query Optimization / Adaptive Statistics - SQL Plan Directives (Oracle 12c)
  • [Oracle] Troubleshooting parallel executions (PX) - What the heck … why is the SQL not executed in full parallelism?
  • [Oracle] DB Optimizer Part IX - Session specific statistics for GTT (global temporary tables) with Oracle 12c
  • [Oracle] Profiling and troubleshooting Oracle related CPU performance issues on Linux with perf (perf_events)
  • [Oracle] Oracle 12c - Architectural change in instance / listener registration process (LREG)
  • [Oracle] DB Optimizer Part VIII - Looking under the hood of query transformation (done by CBO) with simple real life example
  • [Oracle] SQL*Net researching - Setting Session Data Unit (SDU) size and how it can go wrong
  • [SAP] SAP Performance Tuning - Part I - The theoretical approach
  • [Oracle / SAP] Thinking clearly about performance and why ASH / AWR based analysis may not be the right approach
  • [Oracle] DB Optimizer Part VII - Looking under the hood of Adaptive Query Optimization / Adaptive Plans (Oracle 12c)
  • [Oracle] Summary - Exploring Oracle 12c (R1) - Is the sky really cloudy or rather shiny?
  • [Oracle] Myths and common misconceptions about (transparent) huge pages for Oracle databases (on Linux) uncovered
  • [Oracle] Database cache internals and why one data block can use multiple cache buffers
  • [Oracle] DB Optimizer Part VI - Effects of disabled bind variable peeking, adaptive cursor sharing and cardinality feedback on the CBO in SAP environments
  • [Oracle] Wrong SQL_ID in view V$SORT_USAGE / V$TEMPSEG_USAGE and how to handle it in or higher
  • [Oracle] A deeper insight into stack tracing / sampling for a better understanding and troubleshooting of Oracle issues
  • [Oracle] DB Optimizer Part V - Introduction of dynamic sampling and why it is used in SAP BI environments by (SAP) default
  • [Oracle] RMAN (backup) performance with synchronous I/O dependent on OS limitations
  • [Oracle] The importance of a correct (performance) test environment and why LOBs don't generate the expected redo content
  • [Oracle] Unchain database and SQL performance by design (Row Chaining)
  • [Oracle] DB Optimizer Part IV - What the heck ... Troubleshooting why hints are not considered
  • [Oracle] Advanced (performance) troubleshooting with oradebug and stack sampling
  • [Oracle] A short SQL*Net research or how-to drill down network related ORA errors
  • [Oracle] Wait event "library cache lock" by (security) design and exploring system state dumps (oradebug)
  • [Oracle] Insights into redo handling, preemptive redolog switches and "log file switch (private strand flush incomplete)"
  • [Oracle] DB Optimizer Part III - Extending and tuning of execution plans in practice
  • [Oracle] DB Optimizer Part II - Extending execution plans or how-to find the bad one
  • [Oracle] DB Optimizer Part I - Understanding FOR ALL ENTRIES (and its processing by SAP DBSL / Oracle)
  • [Oracle] ANALYZE vs. DBMS_STATS or how-to play tricks on the optimizer
  • [Oracle] Parallel RMAN backup, but RMAN restore not in parallel (with TSM)
  • [Oracle] Real Application Testing with SAP
  • [Oracle] Index key compression
  • [SAP] First experience with SAP BR*Tools Studio for Oracle
  • [Oracle] Running SAP with Oracle Data Guard / - ! Attention !
  • [Oracle] CREATE / REBUILD INDEX ONLINE - Table lock
  • [SAP] R3trans error on AIX with async i/o
  • [Oracle] Migrating SAP systems on Oracle with less effort
  • [Oracle] Tuning "log file syncs" on AIX with DIO/CIO
  • [Oracle] Hinting a SQL without adding a hint
  • [Conference] DOAG 2009 ... see you in Nuremberg
  • Clients & Reviews


    The following list is just an extract of my clients due to particular confidentiality agreements - especially with my US clients. Please contact me for more detailed information.

    Public client reviews

    Stefan is a genuine Oracle database expert with in-depth knowledge and understanding of database internals and optimizer. He is able to efficiently work out a straightforward solution to all kind of different problems around the database, even complex performance bottlenecks, hanging issues and system crashes. If you need a quick solution for an urgent issue with an Oracle database, he is a right consultant to hire.
    Nenad Noveljic, Head Databases and Middleware Engineering & Support, Bank Vontobel AG


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    soocs – SAP on Oracle consulting services
    Stefan Koehler
    Gustav-Freytag-Weg 29
    D-96450 Coburg

    Phone: +49 (0) 172 / 1796830
    Mail: contact{at}
    VAT Reg. No.: DE283352582

    LinkedIn - Stefan Koehler Skype - Cyberfree_ger Twitter - Stefan Koehler Xing Stefan Koehler Oracle Technology Network - Stefan Koehler SAP Comunnity Network - Stefan Koehler 

    Public Appearances


    September 28 - 29, 2016 - Trivadis Performance Days 2016 in Zurich: Talk about Troubleshooting Oracle performance issues beyond Oracle wait interface
    November 15 - 18, 2016 - DOAG 2016 Conference + Exhibition in Nuremberg: Talk about Hacking Oracle's memory - About internals & troubleshooting


    June 16, 2016 - Regional DOAG group meeting in Nuremberg: Talk about Troubleshooting Oracle performance issues beyond Oracle wait interface (Extended Version)
    May 19, 2016 - Regional DOAG group meeting in Nuremberg: Participant & Meet up
    November 17 - 20, 2015 - DOAG 2015 Conference + Exhibition in Nuremberg: Talk about Identifying performance issues beyond Oracle wait interface


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