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Missing wait event

Oracle 11.2.0.1 for Windows is out for some time. I’ve installed it on my 32-bit Windows XP machine because I like Windows – just to check that it’s actually working fine. Playing with TPC-H test using Hammerora I’ve noticed an anomaly in the way Oracle reports IO waits for some queries. Here is a test [...]

SQL*Net compression

Here’s a little demonstration I’ve been meaning to write about for the last few years – it’s very simple: create a table, then query it a few times. execute dbms_random.seed(0) create table t1 as with generator as ( select --+ materialize rownum id from all_objects where rownum <= 3000 ) select lpad(dbms_random.string('U',2),40,'X') v1 from generator [...]

The Ramp

I love stories about performance problems. Recently, my friend Debra Lilley sent me this one:

I went to see a very large publishing company about 6 months after they went live. I asked them what their biggest issue was, and they told me querying in GL was very slow, and I was able to fix quite easily. (There was a very simple concatenated index trick for the Chart of Accounts segments that people just never used.) Then I asked if there was anything else. The manager said no but the clerk who sat behind him said, “I have a problem.” His manager seemed embarrassed, but when I pressed him, the clerk continued, “Every day I throw away reams of paper from our invoice listing.”

cursor: pin S waits, sporadic CPU spikes and systematic troubleshooting

I recently consulted one big telecom and helped to solve their sporadic performance problem which had troubled them for some months. It was an interesting case as it happened in the Oracle / OS touchpoint and it was a product of multiple “root causes”, not just one, an early Oracle mutex design bug and a Unix scheduling issue – that’s why it had been hard to resolve earlier despite multiple SRs opened etc.

Martin Meyer, their lead DBA, posted some info about the problem and technical details, so before going on, you should read his blog entry and read my comments below after this:

Problem:

So, the problem was, that occasionally the critical application transactions which should have taken very short time in the database (<1s), took 10-15 seconds or even longer and timed out.

Symptoms:

The Core Performance Fundamentals Of Oracle Data Warehousing – Parallel Execution

[back to Introduction] Leveraging Oracle’s Parallel Execution (PX) in your Oracle data warehouse is probably the most important feature/technology one can use to speed up operations on large data sets.  PX is not, however, “go fast” magic pixi dust for any old operation (if thats what you think, you probably don’t understand the parallel computing paradigm). With Oracle PX, a large task is broken up into smaller parts, sub-tasks if you will, and each sub-task is then worked on in parallel.  The goal of Oracle PX: divide and conquer.  This allows a significant amount of hardware resources to be engaged in solving a single problem and is what allows the Oracle database to scale up and out when working with large data sets. I though I’d touch on some basics and add my observations but this is by far not an exhaustive write up on Oracle’s Parallel Execution.  There is an entire chapter in the Oracle Database documentation on PX as well as several white papers.  I’ve listed all these in the Resources section at the bottom of this post.  Read them, but as always, feel free to post questions/comments here.  Discussion adds great value. A Basic Example of Parallel Execution [...]

Full House @MOW 2010 in Denmark

Wow, it will be a full house during Miracle OpenWorld 2010, as Moans announced during this video, maybe there won't be enough beds, maybe there won't be enough food, but Moans at least promised us, the 208+ attendees, the new Miracle Brew, anyway, have a look...

Failed Login

Here’s a piece of code I found recently running every half hour on a client site:

SQL_ID = 2trtpvb5jtr53
SELECT
TO_CHAR(current_timestamp AT TIME ZONE :"SYS_B_0", :"SYS_B_1") AS curr_timestamp,
COUNT(username) AS failed_count
FROM
sys.dba_audit_session
WHERE
[...]

Non-trivial performance problems

Gwen Shapira has written an article about a good example of a non-trivial performance problem.

I’m not talking about anything advanced here (such as bugs or problems arising at OS/Oracle touchpoint) but that sometimes the root cause of a problem (or at least the reason why you notice this problem now) is not something deeply technical or related to some specific SQL optimizer feature or a configuration issue. Instead of focusing on the first symptom you see immediately, it pays off to take a step back and see how the problem task/application/SQL is actually used by the users or client applications.

In other words, talk to the users, ask how exactly they experience the problem and then drill down from there.

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WLS + Oracle benchmark – 2

Another press release from Oracle on the same topic: benchmark of WLS 10.3.3 (not released yet) + Oracle 11.2.0.1 @ Dell PowerEdge R910 Server with 4×8-core beasts X7560 (announced today by Intel). Benchmark was done by Oracle itself (previous were conducted by Cisco & HP). Results and FDA are here. DB & WLS configuration are [...]

Oracle Latch Contention Troubleshooting

I wrote a latch contention troubleshooting article for IOUG Select journal last year (it was published earlier this year). I have uploaded this to tech.E2SN too, I recommend you to read it if you want to become systematic about latch contention troubleshooting:

http://tech.e2sn.com/oracle/troubleshooting

I’m working on getting the commenting & feedback work at tech.E2SN site too, but for now you can comment here at this blog entry…

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