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...)
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...)
[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...)
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...)
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...)
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...)
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...)
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...)
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 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...)
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...)
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...)
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...)
To try and keep a longer story as short as possible I needed to package up the Python run time environment to ship along with a Python based application I had written. And in this case the target platform was Windows, though the solution will also work for Linux or any other platform (however most Linux distributions will already have Python on them). I needed to ship Python itself with my application to guarantee that (more...)
Some time ago I dealt with a system that was experiencing high "log file sync" times, as well as other RAC related waits ("gc buffer busy" and "gc cr block busy"). Initially I assumed that the "log file sync" waits and the RAC Global Cache waits were independent of each other, but it turned out that they were interlinked. This post is mainly to make other people aware that on a RAC system there is (more...)
I needed to "play" with Oracle VM and learn how to use it for some upcoming work involving virtual machines. Oracle VM (not VirtualBox) is virtualization software that installs directly onto a system i.e. it installs onto "bare metal" and does not need a host operating system. The problem I had was that I had no "spare" unused system on which I could install Oracle VM. I really wanted to be able to install (more...)
I've previously covered a number of queries that can be combined together to pull out key statistics from the Oracle AWR data for each snapshot it makes, which you could use to analyse the performance of a system. One example would be to use this to look at how the (more...)
This is the last of the main set of posts on this topic. As for the last post, I'll try and keep this brief and post the SQL involved.
Another data set we can look at is on SQL statements i.e. statistics collected by AWR on individual SQL statements, (more...)
So far our AWR report query shows overall duration between two consecutive snapshots, database time (i.e. doing work), SQL execution time (may be lower), total wait time, wait time by class, and some common specific wait events. We know how busy the database was and how much time it (more...)
Given the previous sub-query for total wait times including class level waits from the AWR snapshot data, we are going to extend that particular sub-query in order to add some extra wait event data items to it. This will give us a further breakdown of what the major wait events (more...)