Tanel Poder Blog

Online & Video Training

• Practical Linux Performance & Troubleshooting
• Advanced Oracle Troubleshooting
• Advanced Oracle SQL Tuning

Talks & Videos

• Benchmarking my CatBench Vector Search App on Google AlloyDB (Webinar with Google July 23, 2025)
• Dimensional Analysis of System Performance with eBPF & xtop (Hacking Session Webinar Aug 19, 2025)
• Efficient, Always-On Thread Level Observability with eBPF (P99CONF Oct 22-23, 2025)
• Past Events (Videos)

Latest Articles

• New scripts: vstat.sql & dstat.sql for showing Oracle Sysmetric history with 1-minute granularity
• xb.sql and xbi.sql - Explain Oracle Execution Plans Better! (Part 3 - Cardinality Misestimates)
• Black Friday Sale 2025 Opens Now: All My Flagship Courses Discounted Until the End of 2025!
• New Training Deep Dives: Handling Oracle Optimizer, Partitioning and I/O-Intensive Databases
• tabhisthybrid.sql: Display Oracle hybrid histograms and filter cardinality estimates
• pqr.sql: Generate QR Codes with Pure SQL in PostgreSQL
• The xCapture and xtop eBPF tools are now in beta, with a demo dataset
• CatVector Demo Website
• New Tool: xstack - Completely Passive eBPF Linux Stack Profiling Without Any Tracepoints
• Dimensional Analysis of System Performance with eBPF & xtop: Top for Wall-Clock Time
• Webinar: Testing High-Performance Vector Search With CatBench on Google AlloyDB Omni
• My Blog Has Turned 18 Years Old
• Catbench Vector Search App has Postgres Query Throughput and Latency Monitoring Now
• Using Postgres pg_test_fsync tool for testing low latency writes
• Find which Oracle SQL_ID hits the SQL*Net break/reset to client event
• New Tool: lsds - List All Linux Block Devices and Settings in One Place
• Optimizing eBPF I/O latency accounting when running 37M IOPS on a 384-CPU server
• xCapture v3: Linux Performance Analysis with Modern eBPF and DuckDB
• Core Function Words Translated between English, Spanish, German, French and Swedish
• When eBPF task->stack->pt_regs reads return garbage on the latest Linux kernels, blame Fred!
• TracepointArgs: List Any Linux Tracepoint with Their Arguments, Datatypes and Related Structs
• CatBench Vector Search Playground
• Embedding Vectors of the Same Image Rotated Over 360 Degrees
• SQL Plan Execution FlameGraphs with Loop and Row Counts
• Embedding Vectors vs. Vector Embeddings
• Video: Testing the Silk Platform in 2024 Interview (12 minutes)
• Testing the Silk Platform in 2024: Achieving 20 GiB/s I/O Throughput in a Single Cloud VM
• Visualizing and Comparing Embedding Vectors as Heatmaps (Videos)
• Visualizing and Comparing Embedding Vectors as Heatmaps
• Tracking, not Tracing, Linux Thread Activity for Complete System Visibility (eBPF Summit)
• Python Supports Profiling with Perf - How Does It Work?
• Can a User Process Consume Kernel Mode CPU Without a Syscall?
• Next Big Thing: X-Ray Vision for Linux Systems with eBPF
• Syscallargs: List All Linux System Calls With Their Arguments
• RTX4090 converted into an eGPU
• Oracle Hint Scopes and Join Level Cardinality Hint
• New Commenting System
• Oracle Shared Pool Internals: Allocated Chunk Status Indicators in Heap Dumps
• Oracle Index Parallel Degree Fix After Parallel Creation or Rebuild
• Report Current Oracle Session Wait Chains from GV$SESSION without ASH
• Advanced Oracle Troubleshooting Guide, Part 13: OStackProf for Linux, Unix & MacOSX Clients
• Testing Oracle's Use of Optane Persistent Memory, Part 2 - Fast Log File Sync Waits
• Testing Oracle's Use of Optane Persistent Memory, Part 1 - Low Latency Commits
• MySQL Now Shows its Thread Names at OS Level for Better Troubleshooting
• xb.sql and xbi.sql - Explain Oracle Execution Plans Better! (Part 2)
• My New Learning Platform and What I'm Up To in 2022
• Achieving 10 GB/s Scanning Rate in a Single Cloud VM
• Testing The Silk Platform - Hands-On Technical Analysis of High-Performance I/O in the Cloud
• Virtual Conference: Troubleshooting Very Complex Oracle Performance Problems
• Do Not Use '>' in Your Command Prompt (and How to Stay Safe in Shell)
• Is Your Linux Version Hiding Interrupt CPU Usage From You?
• Video: High Performance Block I/O on Linux
• Achieving 11M IOPS & 66 GiB/s IO on a Single ThreadRipper Workstation
• Oracle Wait Event Name vs. Display Name
• Measuring Java JVM thread activity in Linux with task state sampling
• Reasons why SELECT * is bad for SQL performance
• High System Load with Low CPU Utilization on Linux?
• Hacking Session: 7 Levels of Hint Invalidity in Oracle SQL
• Hacking Session: Oracle SQL Monitoring - Understanding the Execution Timeline column and CPU usage
• Virtual Conference: Systematic Oracle SQL Optimization Interview Videos
• Oracle Fatal Background Processes
• Virtual Conference Update: Systematic Oracle SQL Optimization in 2020
• Oracle Shared Pool Internals: List Chunk Position in the LRU List
• SchedLat: a Low Tech Script for Measuring Process CPU Scheduling Latency on Linux
• Announcing My Retirement (in 2030)!
• ORA-12850: Could not allocate slaves on all specified instances error and a workaround for my scripts
• Oracle Performance Troubleshooting Without OS Access, Part 1: Identifying CPU Scheduling Latency
• Video: Troubleshooting Complex Oracle Performance Problems (Jan 2020)
• Hacking Session: Troubleshooting Complex Oracle Performance Problems (January 2020)
• help.sql: Show TPT Script Purpose and Syntax
• Oracle State Objects and Reading System State Dumps Hacking Session Video
• New scripts: xb.sql and xbi.sql - Explain Oracle Execution Plans Better! (Part 1)
• Dump Current Oracle SQL Execution Plan Line ID Using Oradebug
• pSnapper: Linux Process Snapper Page and Videos
• Announcing Linux Process Snapper tool and a Linux Troubleshooting Hacking Session (3rd April 9am PDT)
• What Caused This Wait Event: Using Oracle's wait_event[] tracing
• Tutorial: Troubleshooting Linux SSH Login Delay - Why does logging in always take 10 seconds?
• Practical Linux Performance & Application Troubleshooting Training Details and Table of Contents
• Scripts for Drilling Down Into Unknown Optimizer Changes
• Visualizing SQL Plan Execution Time With FlameGraphs
• Generate Oracle SQL Monitoring Reports as HTML using SQL Developer v18.3 (no Flash needed)
• Log file switch (checkpoint incomplete) wait events and LGWR waiting for checkpoint progress
• Oracle SQL Monitoring and Advanced ASH Usage Hacking Sessions!
• Oracle SQL Tuning training & Oracle Troubleshooting training and some Linux stuff too!
• Webinar: Troubleshooting a Complex Oracle Performance Issue
• My Performance & Troubleshooting scripts (TPT) for Oracle are now in GitHub and open sourced
• Video: Oracle X$TRACE, Wait Event Internals and Background Process Communication
• Secret Hacking Session: Oracle Background Process Communication, Exotic Wait Events and Some Tracing too
• Advanced Oracle Troubleshooting seminar in 2018!
• Apache Impala Internals Deep Dive with Tanel Poder + Gluent New World Training Month
• GNW01: In-Memory Processing for Databases
• My BIWA Summit Presentations
• RAM is the new disk – and how to measure its performance – Part 3 – CPU Instructions & Cycles
• My New Youtube Channel
• Troubleshooting Another Complex Performance Issue – Oracle direct path inserts and SEG$ contention
• SQL Monitoring in Oracle Database 12c
• Advanced Oracle Troubleshooting v2.5 (with 12c stuff too)
• RAM is the new disk – and how to measure its performance – Part 2 – Tools
• RAM is the new disk – and how to measure its performance – Part 1 – Introduction
• The Hybrid World is Coming
• Old ventures and new adventures
• Advanced Oracle Troubleshooting Guide – Part 12: control file reads causing enq: SQ – contention waits?
• Sqlplus is my second home, part 8: Embedding multiple sqlplus arguments into one variable
• Oracle Exadata Performance: Latest Improvements and Less Known Features
• Oracle In-Memory Column Store Internals – Part 1 – Which SIMD extensions are getting used?
• About index range scans, disk re-reads and how your new car can go 600 miles per hour!
• Combining Bloom Filter Offloading and Storage Indexes on Exadata
• What the heck are the /dev/shm/JOXSHM_EXT_x files on Linux?
• Oracle Memory Troubleshooting, Part 4: Drilling down into PGA memory usage with V$PROCESS_MEMORY_DETAIL
• Slides of my previous presentations
• Where does the Exadata storage() predicate come from?
• Oracle X$ tables – Part 1 – Where do they get their data from?
• cell flash cache read hits vs. cell writes to flash cache statistics on Exadata
• Hard Drive Predictive Failures on Linux and Exadata
• When do Oracle Parallel Execution Slaves issue buffered physical reads – Part 2?
• When do Oracle Parallel Execution Slaves issue buffered physical reads – Part 1?
• Diagnosing buffer busy waits with the ash_wait_chains.sql script (v0.2)
• SGA bigger than the amount of HugePages configured (Linux – 11.2.0.3)
• Why doesn’t ALTER SYSTEM SET EVENTS set the events or tracing immediately?
• Advanced Oracle Troubleshooting Guide – Part 11: Complex Wait Chain Signature Analysis with ash_wait_chains.sql
• Oracle Performance & Troubleshooting Online Seminars in 2013
• Scalar Subqueries in Oracle SQL WHERE clauses (and a little bit of Exadata stuff too)
• ShowMOS: How to get rid of the annoying “The Page has Expired” dialog in My Oracle Support
• Oracle 12c: Scalar Subquery Unnesting transformation
• Oracle Database 12c R1 (12.1.0.1.0) is finally released!
• Getting the Most Out of ASH online seminar
• Forcing Smart Scans on Exadata – is the _serial_direct_read parameter safe to use in production?
• Debugger Dangers – Part 2
• List Exadata Storage Cell disk summary with cellpd.sql and cellpdx.sql scripts
• List Exadata Disk Layout and Topology with the exadisktopo scripts
• V$CELL_THREAD_HISTORY – “ASH” for Exadata Storage Cells
• Understanding what a hint affects using the V$SQL_FEATURE views
• Listing Exadata storage cells and their configuration info from V$CELL_CONFIG
• Alter session force parallel query doesn’t really force anything
• asqlmon.sql: SQL Monitoring-like execution plan line level drilldown into SQL response time
• ExaSnapper 0.7 beta download and the hacking session videos
• Peeking into Linux kernel-land using /proc filesystem for quick’n’dirty troubleshooting
• Even more Snapper – v4.03 now works in SQL Developer too!
• Manual “before” and “after” snapshot support in Snapper v4
• Snapper v4.02 and the Snapper launch party video
• Drilling Deep Into Exadata Performance with ASH, SQL Monitoring and Exadata Snapper – slides and a hacking session!
• Troubleshooting high CPU usage with poor-man’s stack profiler – in a one-liner!
• Session Snapper v4 – The World’s Most Advanced Oracle Troubleshooting Script!
• Sqlplus is my second home: Part 7 – Downloading files via sqlplus :-)
• Japanese translation of some of my blog articles
• What the heck is the INTERNAL_FUNCTION in execution plan predicate section?
• A tip for lazy Oracle users – type less with ANSI DATE and TIMESTAMP SQL syntax
• Snapper v3.61 released – and more work is in progress!
• Select statement generating redo – and lost write detection
• Sqlplus is my second home: Part 6 – Colorizing sqlplus and terminal output
• Optimizer statistics-driven direct path read decision for full table scans (_direct_read_decision_statistics_driven)
• The limitations of CURSOR_SHARING = FORCE and FORCE_MATCHING_SIGNATURE for SQL plan stability
• MOATS-like sqlplus “top” utility for RAC
• Oradebug hanganalyze with a prelim connection and “ERROR: Can not perform hang analysis dump without a process state object and a session state object.”
• Advanced Oracle Troubleshooting Guide – Part 10: Index unique scan doing multiblock reads?!
• Where is LOB data stored?
• Exadata Smart Scan predicate offloading and sequence.NEXTVAL
• Create a database link with the new host:port/service syntax
• Oracle Core: Essential Internals for DBAs and Developers book by Jonathan Lewis
• Profiling trace files with preprocessor external tables in 11g and some parallel execution hacking
• Evil things are happening in Oracle
• What the heck is the SQL Execution ID – SQL_EXEC_ID?
• V8 Bundled Exec call – and Oracle Program Interface (OPI) calls
• Full scans, direct path reads and ORA-8103 error hacking session video
• Are you getting the most out of your Exadata performance? Part 1
• What is the purpose of segment level checkpoint before DROP/TRUNCATE of a table?
• Another cache buffers chains latch contention troubleshooting example using LatchProf
• Tech Reviewer, Tech Reviewer! ;-)
• IOUG Select Journal Editor’s Choice Award 2011
• Knowing what you want to achieve before thinking of how to achieve it – a query optimization example
• Running SELECT … INTO :bind_variable from SQL
• Latch contention troubleshooting case study and Flashback Database performance issues with LOBs
• MOATS: The Mother of All Tuning Scripts!
• An index of my TPT scripts
• LOBREAD SQL Trace entry in Oracle 11.2 (and tracing OPI calls with event 10051)
• Implicit datatype conversion in the parsing phase – something new I learned today!
• ORA-4031 errors, contention, cursor management issues and shared pool fragmentation – free secret seminar!
• Exadata CAN do smart scans on bitmap indexes
• Oracle Exadata Performance series – Part 1: Should I use Hugepages on Linux Database Nodes?
• Finding Oracle Homes which Oracle instances are using on Linux
• New cursor_bind_capture_destination parameter in Oracle 11.2.0.2
• Performance Stories from Exadata Migrations
• Is this valid SQL syntax? :-)
• Snapper 3.52 – With Oracle 9.2 support!
• Asynch descriptor resize wait event in Oracle
• A little new feature for shared pool geeks :-)
• COUNT STOPKEY operation (the where ROWNUM <= N predicate) doesn't process over ~4 Billion rows and returns wrong results
• Read currently running SQL statement’s bind variable values using V$SQL_MONITOR.BIND_XML in Oracle 11.2
• The most fundamental difference between hash and nested loop joins
• Oracle Closed World presentation links
• Which number takes more space in an Oracle row?
• Exadata v2 Smart Scan Performance Troubleshooting article
• Dropping and creating tables in read only tablespaces?!
• The full power of Oracle’s diagnostic events, part 2: ORADEBUG DOC and 11g improvements
• Oracle memory troubleshooting article
• Flexible Sqlplus command line history with RLWRAP
• Execution plan Quiz: Shouldn’t these row sources be the other way around ;-)
• Quiz: Explaining index creation
• cursor: pin S waits, sporadic CPU spikes and systematic troubleshooting
• KGH: NO ACCESS – Buffer cache inside streams pool too!
• Non-trivial performance problems
• Calculate SQL_ID and SQL_HASH_VALUE from SQL text
• Oracle Latch Contention Troubleshooting
• Oracle Session Snapper v3.10
• How to CANCEL a query running in another session?
• New versions of LatchProf and LatchProfX for latch contention troubleshooting and tuning
• Oracle Troubleshooting: How to read Oracle ERRORSTACK output?!
• Using Process Memory Matrix script for calculating Oracle process memory usage on Solaris
• Oracle Wait Event reference
• Oracle Peformance Visualization…
• Bind Variable Peeking – execution plan inefficiency
• Recursive sessions…
• Sometimes things are easy (Part 1): How to fix wrapped execution plan text?
• Beyond Oracle Wait Interface – Part 2
• NULL is not zero!
• Measuring what matters
• Finding the reasons for excessive logical IOs
• Explain Plan For command may show you the wrong execution plan – Part 1
• Detect chained and migrated rows in Oracle – Part 1
• What’s a good way to learn some Oracle internals every day?
• SystemTap is production supported in Redhat EL5.4
• KGL simulator, shared pool simulator and buffer cache simulator – what are these?
• KGH: NO ACCESS allocations in V$SGASTAT – buffer cache within shared pool!
• Oracle 11gR2 has been released – and with column oriented storage option
• latch: cache buffers chains latch contention – a better way for finding the hot block
• Select COUNT(*) and COUNT(column) are different things!
• Alter system kill session and ORA-00031: session marked for kill
• An interview with me
• How to detect when a cursor was closed from SQL trace output?
• Identify the SQL statement causing those WAIT #X lines in a (top-truncated) sql tracefile
• (Secret) Preview of Oracle 12g CBO leaked from Oracle labs…
• Oracle memory troubleshooting, Part 3: Automatic top subheap dumping with heapdump
• Using Perfsheet and TPT scripts for solving real life performance problems
• ORA-04031 errors and monitoring shared pool subpool memory utilization with sgastatx.sql
• Oracle Performance Visualization videos from Sydney
• Scripts for showing execution plans via plain SQL and also in Oracle 9i
• “Free” DBA_HIST AWR views in 11g…
• I have been troubleshooting since I was a kid! :)
• Tracing Oracle SQL plan execution with DTrace
• Seminar feedback and pictures from Singapore
• Read OS environment variables using DBMS_SYSTEM.GET_ENV()
• I’m an Oracle ACE Director now :)
• Oracle 11g: Reading alert log via SQL
• Another LatchProfX use case
• The real history of Oracle database revealed!
• Oracle, Timesten and PL/SQL support
• The full power of Oracle’s diagnostic events, part 1: Syntax for KSD debug event handling
• 60000 bind variables?! Maybe it’s time to use a temporary table instead…
• SQL_ID is just a fancy representation of hash value
• Performance Visualization, Capacity planning and Hotsos Symposium
• When was a table last changed?
• Multipart cursor subexecution and PRECOMPUTE_SUBQUERY hint
• Identifying shared memory segment users using lsof
• Reliable latch waits and a new blog
• Oracle memory troubleshooting, Part 1: Heapdump Analyzer
• Performance Visualization made easy – PerfSheet 2.0 beta
• A little oradebug enhancement in Oracle 11g
• Advanced Oracle Troubleshooting Guide, Part 9 – Process stack profiling from sqlplus using OStackProf
• Transportable tablespaces and ROWID uniqueness
• VLDB 2008 proceedings, Oracle optimizer plan stability, adaptive cursor sharing and SecureFiles
• Oracle hidden costs revealed, Part2 – Using DTrace to find why writes in SYSTEM tablespace are slower than in others
• Flexible sampling of any V$ or X$ view with sample.sql
• Case study on some rowcache internals, cached non-existent objects and a describe bug
• Why does even a small difference in SQL text cause a hard parse?
• Script: Display valid values for multioption parameters (including hidden parameters)
• The simplest query for checking what’s happening in a database
• Library cache latches gone in Oracle 11g
• Advanced Oracle Troubleshooting Guide, Part 8: Even more detailed latch troubleshooting using LatchProfX
• Closed database and WITH subquery
• Advanced Oracle Troubleshooting Guide, Part 7: Sampling latch holder statistics using LatchProf
• Another use case for WaitProf – diagnosing “events in waitclass Other”
• Killing an Oracle process from inside Oracle
• cursor_space_for_time To Be Deprecated
• Advanced Oracle Troubleshooting Guide, Part 6: Understanding Oracle execution plans with os_explain
• Debugger dangers
• Short note on KGX Mutexes
• Generating lots of rows using connect by – safely!
• Advanced Oracle Troubleshooting Guide, Part 5: Sampling V$ stuff with WaitProf. Really fast. Using SQL!
• Performance Tools Quick Reference Guide
• Advanced Oracle Troubleshooting Guide, Part 4: Diagnosing a long parsing issue
• Snapper shortcut
• Querying the current tracefile name, using SQL – with tracefile_identifier
• Oracle Troubleshooting with Snapper – detecting who’s causing excessive redo generation
• Performance and Scalalability Improvements in Oracle 10g and 11g
• Using autonomous transactions for sleeping
• SQL*Net break/reset to client
• SQL*Net message to client vs SQL*Net more data to client
• SQL*Net message to client wait isn’t really what it’s thought to be
• Oracle hidden costs revealed, part 1 – Does a batch job run faster when executed locally?
• Excellent article on Oracle 11g PL/SQL function result cache
• Can you write a working SQL statement without using any whitespace?
• Expensive calculator…
• Why does Oracle parameter count change during session lifetime?
• Systematic application troubleshooting in Unix
• Perl version of Snapper
• Sqlplus is my second home, part 5: Reading the name of currently executing script
• Oracle Security, Part 2: Your read only accounts aren’t that read only
• Sqlplus is my second home, part 4: Getting sqlplus parameter value into a variable
• A simple interview question
• How to resolve SQL object and column names all the way to base tables and columns in Oracle?
• Advanced Oracle Troubleshooting Guide, Part 3: More adventures in process stack
• Sqlplus is my second home, part 3: Colored selections in Windows XP command prompt
• Sqlplus is my second home, part 2: Running SQL scripts from remote locations using HTTP
• Operating systems are lazy allocating memory
• Advanced Oracle Troubleshooting Guide, Part 2: No magic is needed, systematic approach will do
• Oracle Session Snapper, part 2: Getting most out of Snapper
• Oracle 11g internals part 1: Automatic Memory Management
• Oracle Session Snapper – real-time session-level performance stats for DBAs
• Sqlplus is my second home, Part 1: HTMLizing your sqlplus output
• Session-level statspack
• A gotcha with parallel index builds, parallel degree and query plans
• My version of SQL string to table tokenizer
• Advanced Oracle Troubleshooting Guide: When the wait interface is not enough [part 1]