Oracle JET and WebSocket Integration for Live Data

I was researching how to plugin WebSocket into JET. I would like to share my findings and explain how it works. It is amazing, how scalable and quick it is to send JSON message through WebSocket channel and render it in JET. Luckily WebSocket client is implemented in JavaScript, this integrates perfectly with Oracle JET (also based on JavaScript).

Watch recorded demo, where I'm sending updated data with JSON message through WebSocket. UI chart is (more...)

The Oracle wait interface granularity of measurement

The intention of this blogpost is to show the Oracle wait time granularity and the Oracle database time measurement granularity. One of the reasons for doing this, is the Oracle database switched from using the function gettimeofday() up to version 11.2 to clock_gettime() to measure time.

This switch is understandable, as gettimeofday() is a best guess of the kernel of the wall clock time, while clock_gettime(CLOCK_MONOTONIC,…) is an monotonic increasing timer, which means it (more...)

Friday Philosophy – Database Performance is In My Jeans

Database performance is in my jeans. Not my genes, I really do mean my jeans – an old pair of denim trousers. I look at my tatty attire keeping my legs warm and it reminds me of Oracle database performance.

comfortable, baggy, old, DW jeans

comfortable, baggy, old, DW jeans

You can buy jeans in a range of styles & sizes. Just as you can set up your database in a number of standard ways. When you create a database (more...)

Parallel DML

A recent posting on OTN presented a performance anomaly when comparing a parallel “insert /*+ append */” with a parallel “create table as select”.  The CTAS statement took about 4 minutes, the insert about 45 minutes. Since the process of getting the data into the data blocks would be the same in both cases something was clearly not working properly. Following Occam’s razor, the first check had to be the execution plans – when (more...)


This is just a little example of thinking about hinting for short-term hacking requirements. It’s the answer to a question that came up on the Oracle-L listserver  a couple of months ago (Oct 2015) and is a convenient demonstration of a principle that can often (not ALWAYS) be applied as a response to the problem: “I can make this query work quickly once, how do I make it work quickly when I make it part (more...)

PL/SQL context switch, part 2

This is the second blogpost on using PL/SQL inside SQL. If you landed on this page and have not read the first part, click this link and read that first. I gotten some reactions on the first article, of which one was: how does this look like with ‘pragma udf’ in the function?

Pragma udf is a way to speed up using PL/SQL functions in (user defined function), starting from version 12. If you want (more...)

Linux Perf Probes for Oracle Tracing

Topic: this post is about Linux perf and uprobes for tracing and profiling Oracle workloads for advanced troubleshooting.


The recent progress and maturity of some of the Linux dynamic tracing tools has raised interest in applying these techniques to Oracle troubleshooting and performance investigations. See Brendan Gregg's web pages for summary and future developments on dynamic traces for Linux. Some recent work on applying these tools and techniques to Oracle can be found (more...)

Flame Graphs Vs. Cold Numbers

Stack trace sampling is very powerful technique for performance troubleshooting. Advantages of stack trace sampling are

  • it doesn't require upfront configuration
  • cost added by sampling is small and controllable
  • it is easy to compare analysis result from different experiments

Unfortunately, tools offered for stack trace analysis by stock profilers are very limited.

Solving performance problem in complex applications (a lot of business logic etc) is one of my regular challenges. Let's assume I have another (more...)

PL/SQL context switch

Whenever you use PL/SQL in SQL statements, the Oracle engine needs to switch from doing SQL to doing PL/SQL, and switch back after it is done. Generally, this is called a “context switch”. This is an example of that:

-- A function that uses PL/SQL 
create or replace function add_one( value number ) return number is
        l_value number(10):= value;
        return l_value+1;
-- A SQL statement that uses the PL/SQL function
select sum(add_one(id))  (more...)

Database Change Notification Listener Implementation

Oracle DB could notify client, when table data changes. Data could be changed by third party process or by different client session. Notification implementation is important, when we want to inform client about changes in the data, without manual re-query. I had a post about ADS (Active Data Service), where notifications were received from DB through change notification listener - Practical Example for ADF Active Data Service. Now I would like to focus on change (more...)

Getting Your Transaction SCN – USERENV(COMMITSCN)

A few days ago I was introduced (or re-introduced) to USERENV(‘COMMITSCN’) by Jonathan Lewis. This is an internal function that allows limited access to the SCN of your transaction.

I was trying to find a way to get the actual commit SCN easily as it struck me that Oracle would have it to hand somewhere and it would be unique to the change and generated very efficiently. I could not find anything to do it (more...)

Drop Column

I published a note on AllthingsOracle a few days ago discussing the options for dropping a column from an existing table. In a little teaser to a future article I pointed out that dropping columns DOESN’T reclaim space; or rather, probably doesn’t, and even if it did you probably won’t like the way it does it.

I will  be writing about “massive deletes” for AllthingsOracle in the near future, but I thought I’d expand on (more...)

DML Operations On Partitioned Tables Can Restart On Invalidation

It's probably not that well known that Oracle can actually rollback / re-start the execution of a DML statement should the cursor become invalidated. By rollback / re-start I mean that Oracle actually performs a statement level rollback (so any modification already performed by that statement until that point gets rolled back), performs another optimization phase of the statement on re-start (due to the invalidation) and begins the execution of the statement from scratch. Note (more...)

Introducing stapflame, extended stack profiling using systemtap, perf and flame graphs

There’s been a lot of work in the area of profiling. One of the things I have recently fallen in love with is Brendan Gregg’s flamegraphs. I work mainly on Linux, which means I use perf for generating stack traces. Luca Canali put a lot of effort in generating extended stack profiling methods, including kernel (only) stack traces and CPU state, reading the wait interface via direct SGA reading and kernel stack traces and getting (more...)

“Say What?!?!?”

"The only thing you can do easily is be wrong, and that's hardly worth the effort." 
Norton Juster, The Phantom Tollbooth

Oracle can lie to you. Not like a disreputable uwed-car salesman but more like the ‘little white lie’ sometimes told in order to hide less-than-desirable parts of the truth. And it’s not Oracle, really, it’s the optimizer and it does it by reporting query plans that may not accurtely report the execution path. (more...)

Extended Stack Profiling – Ideas, Tools and Comments

Topic: This post provides a short summary and pointers to previous work on Extended Stack Profiling for troubleshooting and performance investigations.

Understanding the workload is an important part of troubleshooting activities. We seek answers to questions like: what is the system doing, where is the time spent, which code paths are most used, what are the wait events, etc. Sometimes the relevant diagnostic data is easy to find, other times we need to dig (more...)

New Version Of XPLAN_ASH Utility

A new version 4.22 of the XPLAN_ASH utility is available for download.

As usual the latest version can be downloaded here.

This version primarily addresses an issue with 12c - if the HIST mode got used to pull ASH information from AWR in 12c it turned out that Oracle forgot to add the new "DELTA_READ_MEM_BYTES" columns to DBA_HIST_ACTIVE_SESS_HISTORY - although it got officially added to V$ACTIVE_SESSION_HISTORY in 12c. So now I had to implement (more...)

Oracle 12 and latches, part 3

This post is about manually calling and freeing a shared latch. Credits should go to Andrey Nikolaev, who has this covered in his presentation which was presented at UKOUG Tech 15. I am very sorry to see I did miss it.

Essentially, if you follow my Oracle 12 and shared latches part 2 blogpost, which is about shared latches, I showed how to get a shared latch:

SQL> oradebug setmypid
Statement processed.
SQL> oradebug  (more...)

OGh DBA / SQL Celebration Day 2016

During next year’s annual OGh DBA day (the 7th of June 2016), additional presentations will…

Unindexed Foreign Keys on empty/unused table and locks

It is widely known that unindexed foreign keys can be performance issue. Unindexed foreign keys on child tables can cause table locks or performance problems in general.
There are many articles on this subject so I won't go in details.

My plan is to show simple demo case where empty child table with unindexed foreign key column can cause big problems.

Imagine that you have highly active table (supplier) with lots DML operations from many (more...)