Chatty Applications and Simple SQL

One type of "poor performance" scenario I have come across a few times is due to what I call "chatty applications". These are applications that execute a disproportionally high number of what look like very simple SQL queries for every business transaction they do. And often this is a deliberate design choice by the application architects and developers, claiming that simpler SQL statements on single tables using indexed columns always leads to efficient (more...)

Redundant Grandparent Foreign Keys and Cardinality Estimate Errors

This post is about how a slightly de-normalized database design involving redundant foreign keys to other tables can end up producing sub-optimal execution plans for queries that use those extra joins as additional filter conditions.

By default the Oracle Optimizer assumes that different columns of data in a table are independent of each other, and that their data values are not correlated with each other in any way. When a query has filter conditions on (more...)

I’m back, again, late 2017

Nothing much to say other then I'm back again, and hope to do some more blog posting soon. My excuse for the lack of posts is that I've been busy helping a client with a large data migration project. That is now over, with all the data successfully extracted for loading into their new system, so I've got more time available to properly write up some technical Oracle or performance posts.

Fixing Popular Posts Margin on Blogger

I use the Blogger platform for this blog, and I recently added the "Popular Posts" widget to the sidebar. Unfortunately it did not display correctly, with the first character or two of each blog post title being lost and chopped off, as if the whole thing had been shifted to the left for some reason. Here is how I fixed it to display properly.

After a lot of reading up on HTML and (more...)

Announcing Bottleneck Data Solutions

SPOILER ALERT: This particular blog post is a blatant self promotion for me and the various Oracle database services I am offering.

I may not have mentioned it explicitly before but I have left the corporate world of permanent employment and have gone independent to offer my services direct to clients (at reasonable rates, of course). I'm doing this through my newly created company Bottleneck Data Solutions, which has its own associated, obligatory web (more...)

When 2 Queries Are Better Than 1

A general rule of thumb with queries in Oracle is to use just one query when you can and leave it to the Optimizer to work out the best possible execution plan i.e. decomposing one query into multiple separate queries can end up making the database do more work than it needs to. I came across a case the past week where the opposite was true - making Oracle do separate "smaller" queries was (more...)

AWR Summary Data Extracts

A long time ago (in a galaxy far away) I wrote a series of blog posts about directly extracting useful sets of data from the AWR snapshots in the DBA_HIST tables for subsequent analysis and graphing using things like Excel. This post is to summarise where I got to on this, and provide links back to the main posts for future reference.

A guiding principle of my approach was that I wanted to avoid the (more...)

Full Table Scan not always as low as 0.5% of data!

Based on a reply from Jonathan Lewis to an OTN post on Explain Plans I need to correct some of the claims made in my previous post on Full Table Scans.

I'm going to repeat the inaccurate paragraphs and the Conclusions I posted then [edited here for brevity], and then point out the mistakes in them, and an attempt at a corrected set of paragraphs. I will also edit the original post and replace these (more...)

Creeping Slow Performance

A recent OTN post requesting help for a slow performing update where Oracle was doing a full table scan, also revealed that the update was getting slower and slower each month, and that new data was loaded into the table each month to be "processed" i.e. updated. Unfortunately this kind of design suffers from a natural creeping slowdown in the elapsed time of the update process. Each month it will take longer and longer (more...)

Full Table Scan – Friend or Foe?

[Or Don't be afraid of Full Table Scans]

Many people consider a Full Table Scan (FTS) in a query execution plan to be a bad thing - reading every record from a table to find only those records the query needs. This is indicated by a "TABLE ACCESS FULL" in an execution plan. But is it really all that bad? Is it actually sometimes the right tool for the job? Can a Full (more...)

What’s Going On? Oracle Activity Monitoring Views

How do you find out what is happening now inside an Oracle database instance when you only have SQL level access to the database instance, and no nice GUI management tool? I'll cover how to start doing this with some SQL query examples.

A user is complaining that the application is running slowly, or a report someone scheduled is taking too long to finish - where do you look to find out what is going (more...)

GRUB, os-prober and Red Hat / Oracle Linux

I've been successfully using VirtualBox to have test environments to run Oracle Linux and Oracle Database in from some time, but there are limitations to what you can do. So I decided that I wanted to install Oracle Linux onto another disk partition on my PC so I could dual boot into it for some more advanced Oracle Database tests. Well the Oracle Linux installation itself went ahead trouble free - I just had to (more...)

Oracle In Memory and CPU Execution Efficiency

Tanel Poder has been doing a series of posts on "RAM is the new disk" trying to show how the new "Oracle Database In-Memory" feature in Oracle 12c uses memory in a different and more efficient way than the normal, traditional buffer cache does. He hasn't finished the series of posts yet, but I started to draw some of my own conclusions from the data he published in his last post (more...)

Python for the DBA (2) – Data Unloading

I've mentioned before that I like the Python programming language. Not only is it a "clean" language for writing programs in with a rich set of data types and structures for manipulating data, it also has a standard API for database access making it "database neutral". This makes it relatively easy to get data that is in a database into and out of your Python code where you can use the power of Python for (more...)

Use Bind Variables in Application SQL for Oracle

If you don't already know, then you should almost always be using bind variables in all SQL statements used in any applications you write that run against Oracle. Bind variables are place holders within your SQL statements that get replaced by real data values at run time when the SQL statement is executed i.e. at run time the real data value is "bound" to the corresponding place holder variable in the SQL statement. So (more...)

Data Driven or Application Driven Development?

I'm the kind of person who believes that Data is really important and needs to be treated and dealt with properly. Of course we also need Applications that use that Data - one without the other is no use at all. But a battle I often have with clients now is that Data needs to be modelled and designed at the same stage as the Application is. Ignore the data model and database design and (more...)

JSON, Python & Trello

JSON is a simple data storage format intended to allow easy data interchange between programs and systems. Data is stored in a text format as objects of "name : value" pairs. And that's about it, other than objects can be nested (a value could be another whole object) and multiple objects can occur one after another in the data set (a list or array of such objects). This makes it slightly database like because you (more...)

Getting My Passion Back

I've been quiet for a long while on this blog because I had been working for a company that just did not get databases at all, and it has been a real energy sapper dealing with the consequences of all of the wrong decisions they kept making.  I'll spare you the gory details, but the biggest problems of many were the wholesale adoption of Agile Development (Scrum) with no training, support or planned cutover (more...)

Red Gate Source Control for Oracle

The background to this - I was "given" a free license to Red Gate Source Control for Oracle some months ago as part of some marketing and awareness activity Red Gate were doing. I've been busy with other things, so I've only now got around to trying to understand what the product does and see if it can be of any benefit to me. Hence this review.

Before I start my review I want to (more...)

Speeding up Imports

There are a number of techniques you can use to speed up an Oracle Import, some of which I'll describe here. This is not any attempt at a comprehensive list, just some of the main techniques I have used that can really speed up some parts of an import. I've seen a standard import come down from 2.5 hours to about 0.75 hours using these techniques.

The first thing to realise is that (more...)