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August 2019

Little things worth knowing: keeping enq: TM enqueue at bay during direct path inserts

Direct path inserts are commonly found in processing where data are shifted from one source to another. There are many permutations of the theme, this post details the way SQL Loader (sqlldr) behaves.

I have previously written about sqlldr and concurrent direct path inserts. The behaviour for releases <= 12.1 is described in the first post, the most welcome changes in 12.2 went into the second post. Since the fastest way of doing something is not to do it at all, I thought it might be worth demonstrating a useful technique to keep the dreaded TM enqueue at bay. Please note that these do not only apply to sqlldr, inserts with the append hint for example behave the same way in my experience.

Getting started with Hyper-V on Windows 10

Microsoft Windows 10 comes with its own virtualization software called Hyper-V. Not for the Windows 10 Home edition, though.

Check if you fulfill the requirements by opening a CMD shell and typing in systeminfo:

Oracle 19c Automatic Indexing: How Many Executions Does It Take? (One Shot)

One of the first questions I asked when playing with the new Oracle Database 19c Automatic Indexing feature was how many executions of an SQL does it take for a new index to be considered? To find out, I create the following table: I then ran the following query just once and checked to see […]

An Oracle Auto Index function to drop secondary indexes - what is a “secondary” index?

dbms_auto_index.drop_secondary_indexes

In 19.4 the Auto Index package has 4 procedure/functions:

Speaking at Trivadis Performance Days 2019

I’ll again be speaking at the wonderful Trivadis Performance Days 2019 conference in Zurich, Switzerland on 26-27 September. There’s again another fantastic lineup of speakers, including: CHRISTIAN ANTOGNINI IVICA ARSOV MARK ASHDOWN SHASANK CHAVAN EMILIANO FUSAGLIA STEPHAN KÖHLER JONATHAN LEWIS FRANCK PACHOT TANEL PODER DANI SCHNIDER   I’ll be presenting two papers: “Oracle 18c and […]

AW-argh

This is another of the blog notes that have been sitting around for several years – in this case since May 2014, based on a script I wrote a year earlier. It makes an important point about “inconsistency” of timing in the way that Oracle records statistics of work done. As a consequence of being first drafted in May 2014 the original examples showed AWR results from 10.2.0.5 and 11.2.0.4 – I’ve just run the same test on 19.3.0.0 to see if anything has changed.

 

Troubleshooting

A recent thread on the Oracle Developer Community starts with the statement that a query is taking a very long time (with the question “how do I make it go faster?” implied rather than asked). It’s 12.1.0.2 (not that that’s particularly relevant to this blog note), and we have been given a number that quantifies “very long time” (again not particularly relevant to this blog note – but worth mentioning because your “slow” might be my “wow! that was fast” and far too many people use qualitative adjectives when the important detail is quantative). The query had already been running for 15 hours – and here it is:

A new use for DML error logging

Many moons ago I did a short video on the DML error logging feature in Oracle. The feature has been around for many years now, and is a great tool for capturing errors during a large load without losing all of the rows that successfully loaded. You can watch that video below if you’re new to DML error logging.

But here is a possible new use case for DML error logging, even if you are not doing large scale loads. Let me describe the problem first, and then show how DML error logging might be a solution.

I’ll create a table with a constraint on it’s column

Optimizer Tricks 1

I’ve got a number of examples of clever little tricks the optimizer can do to transform your SQL before starting in on the arithmetic of optimisation. I was prompted to publish this one by a recent thread on ODC. It’s worth taking note of these tricks when you spot one as a background knowledge of what’s possible makes it much easier to interpret and trouble-shoot from execution plans. I’ve labelled this one “#1” since I may publish a few more examples in the future, and then I’ll have to catalogue them – but I’m not making any promises about that.

Here’s a table definition, and a query that’s hinted to use an index on that table.

Speaking at Oracle OpenWorld 2019

It’s been remarkably 9 years since I’ve been to Oracle OpenWorld, but will finally get the opportunity to present there again this year (with many thanks to the Oracle ACE Director program for making this possible). Details of my presentation are as follows: Conference: Oracle OpenWorld Session Type: Conference Session Session ID: CON1432 Session Title: […]