Friday Philosophy – Explaining How Performance Tuning Is Not Magic?

Solving performance issues is not magic. Oh, I’m not saying it is always easy and I am not saying that you do not need both a lot of knowledge and also creativity. But it is not a dark art, at least not on Oracle systems where we have a wealth of tools and instrumentation to help us. But it can feel like that, especially when you lack experience of systematically solving performance issues.

SQL statement (more...)

Oracle Database Physical I/O IOPS And Throughput Benchmark

General Information

I've used a similar set of scripts quite a few times now to provide feedback to customers that wanted to get a more realistic picture of the I/O capabilities from a database perspective, rather than relying on artificial benchmarks performed outside - or even inside, think of I/O calibration - the database. Although there are already several Oracle benchmark toolkits available, like Swingbench and in particular SLOB, that run inside the database I (more...)

A look into Oracle redo, part 5: the log writer writing

| Feb 27, 2018

This the the fifth blog in a series of blogposts about Oracle database redo. The previous blog looked into the ‘null write’ (kcrfw_do_null_write actually) function inside kcrfw_redo_write_driver, which does housekeeping like updating SCNs and posting processes if needed, this blog looks into what happens when the log writer is actually posted by a process or if public redo strand buffers have been written into. In part 3 of this blog series (the log writer working (more…)

Oracle Exadata Smart Flash Logging

What is Exadata Smart Flash Logging?

In an OLTP environment, it is crucial to have fast response times to redo log writes i.e. low latency.  When multiplexing redo logs for high availability i.e. to protect against hardware failure, redo log writes are only acknowledge when redo is written to all redo log members i.e when the slowest disk completes the write.  By this nature, whenever a disk slows down even (more...)

Adapting and adopting SQL Plan Management (SPM)

Introduction

This post is about: “Adapting and adopting SQL Plan Management (SPM) to achieve execution plan stability for sub-second queries on a high-rate OLTP mission-critical application”. In our case, such an application is implemented on top of several Oracle 12c multi tenant databases, where a consistent average execution time is more valuable than flexible execution plans. We successfully achieved plan stability implementing a simple algorithm using PL/SQL calling DBMS_SPM public APIs.

Chart below depicts a typical (more...)

Friday Fun SQL Lesson – union all

Our office kitchen is unavailable this Friday, so the call was put out for pub lunch.

After a couple of replies I decided to enter my reply, in full nerd mode.
select * from people_coming_to_lunch;

People
--------
Kate
Scott
Karolina

3 rows selected.
And of course one of the other SQL geeks (name redacted) replied to extend the data set.
select * from people_coming_to_lunch
union
select 'Shanequa'
from dual;
And I couldn't help myself. I (more...)

Creating a SQL Plan Baseline from Cursor Cache or AWR

A DBA deals with performance issues often, and having a SQL suddenly performing poorly is common. What do we do? We proceed to “pin” an execution plan, then investigate root cause (the latter is true if time to next fire permits).

DBMS_SPM provides some APIs to create a SQL Plan Baseline (SPB) from the Cursor Cache, or from a SQL Tuning Set (STS), but not from the Automatic Workload Repository (AWR). For the latter, you (more...)

Purging a cursor in Oracle – revisited

A few years ago I created a post about “how to flush a cursor out the shared pool“, using DBMS_SHARED_POOL.PURGE. For the most part, this method has helped me to get rid of an entire parent cursor and all child cursors for a given SQL, but more often than not I have found than on 12c this method may not work, leaving active a set of cursors I want to flush.

Script below (more...)

Baselines – session creating privs v session running privs

A colleague Richard Wilkinson was telling me about an issue he had come across with baselines and I asked him to write it up as it was an interesting experience.

The following MERGE SQL runs once a day. It always uses the same plan and roughly takes between 30 and 80 minutes:

SQL_ID/ PHV 6zs5dk6t6pkfs / 3064471754

 MERGE INTO DWB_X_PLNGRM_ATTR_DAY t
 USING (
 SELECT ilv.bsns_unit_cd,
 ilv.sku_item_nbr,
 ilv.cntnt_cd ,
 ilv.sel_units_cntnt_status,
 ilv.plngrm_item_grp_cd,
  (more...)

ADF Performance on Docker – Lighting Fast

ADF performance depends on server processing power. Sometimes ADF is blamed for poor performance, but in most of the cases real issue is related to poor server hardware, bad programming style or slow response from DB. Goal of this post is to show how fast ADF request could execute and give away couple of suggestions how to minimize ADF request time. This would apply to ADF application running on any environment, not only Docker. I'm (more...)

ADF Performance Story – This Time Developer Was Wrong

ADF is fast. If ADF application is slow, most likely this is related to development mistakes. I would like to tell you one story, based on my ADF tuning experience. Problem description: ADF application runs fast in DEV, when DB size is small. Same application runs slow in TEST/PROD, when DB size is large. Question - what is slow. Answer - slow means forms are loading slow. Ok, lets go to the story.

Developer decides (more...)

Beware of intensive slow query logging when using – log_queries_not_using_indexes

MySQL slow query log is great for identifying slow queries that are good candidates for optimisation. Slow query logging is disabled by default, but it is activated by DBA's or developers on most environments.

You can use slow query log to record all the traffic but be careful with this action as logging all traffic could be very I/O intensive and could have negative impact on general performance. It is recommended to record all traffic (more...)

Oracle and the Autonomous Database (a personal perspective from afar)

Yeah, if you hadn’t seen that one coming, hmmm, what can I say… Lot’s of…

nVision Performance Tuning: Table of Contents

This post is an index for a series of blog posts that discuss how to get good performance from nVision as used in General Ledger reporting.  As the posts become available links will be updated in this post.
  • Introduction
  • nVision Performance Options
  • Indexing of Ledger, Budget and Summary Ledger Tables
  • Partitioning of Ledger, Budget and Summary Ledger Tables
  • Additional Oracle Instrumentation for nVision
  • Logging Selector Usage
  • Analysis of Tree Usage  with the Selector Log
  • Interval (more...)

Autonomous Online Index Rebuild for Oracle Multitenant

First things first: Do not rebuild Oracle indexes! … Unless you have to.

If you are even considering rebuilding indexes on an autonomous manner, please stop now, and first spend some time reading some of the many things Richard Foote has to say on his well-recommended blog.

A little side story: Many, many years ago, as I was supporting EBS at Oracle, one day I got a call from a guy with an aussie accent (more...)

Performance Analysis of a CPU-Intensive Workload in Apache Spark

Topic: This post is about techniques and tools for measuring and understanding CPU-bound and memory-bound workloads in Apache Spark. You will find examples applied to studying a simple workload consisting of reading Apache Parquet files into a Spark DataFrame.
 

Why are the topics discussed here relevant

Many workloads for data processing on modern distributed computing architectures are often CPU-bound. Typical servers underlying current data platforms have a large and increasing amount of RAM and (more...)

Parallel Reality


"Expect everything, I always say, and the unexpected never happens."
-- Norton Juster, The Phantom Tollbooth

The following question was recently posted in an Oracle forum:


hi Friends,
I see  this wait event latch: parallel query alloc buffer, when a job meant for doing some cleanup ran this query.
Why does this wait event come happen? , i searched google,MOS no exact hit for explanation of the exact same event.
Looking at query does  (more...)

Validate Performance Improvement Using Query Folding Feature in Power BI

I’ve been using Power BI for a couple months now, not as a developer, but as a system architecture. I may not deal with dashboard and report development on a daily basis, however, I, as an end user, use Power BI extensively to monitor Azure and Power BI usage including audit and billing. I would like to learn more about this tool to its nuts and bolts. The intention of this blog series is to (more...)

Diving into Spark and Parquet Workloads, by Example

Topic: In this post you can find a few simple examples illustrating important features of Spark when reading partitioned tables stored in Parquet, in particular with a focus on performance investigations. The main topics covered are:
  • Partition pruning
  • Column projection
  • Predicate/filter push-down
  • Tools for investigating Parquet metadata
  • Tools for measuring Spark metrics

Motivations: The combination of Spark and Parquet currently is a very popular foundation for building scalable analytics platforms. At least this is what (more...)

OGh Tech Experience 2017 – recap

On June 15th and 16th 2017 the very first OGh Tech Experience was held. This 2-day conference was a new combination of the DBA Days and Fusion Middleware Tech Experience that were held in previous years. To summarize: OGh hit bullseye. It was two days packed with excellent in-depth technical sessions, good customer experiences and great networking opportunities.

The venue was well chosen. De Rijtuigenloods in Amersfoort is a former maintenance building of the Dutch (more...)