Wednesday, 26 March 2014

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 make two things clear. The first thing is about how you treat Databases in a software development world. Databases are fundamentally different to Application Software. Whereas Application Software is normally rebuilt each time by compiling it from its source code, Databases are never rebuilt - they are always modified in place. A customer's data cannot be thrown away and replaced by a new empty database. Changes to the database must happen in place, in an incremental way. To put it another way, Application Software evolves between each release, with each release being a next generation that replaces the one before it. Databases though metamorphose between releases, with changes being applied directly to the database so that it changes in place and existing data is retained.

This means that a Database must be maintained through a series of "change scripts" that make incremental changes to the database, and these change scripts must be run in a controlled sequence when upgrading the database from one version of its associated Application Software to another version. I would expect any "Database Source Code Control" tool to help in the production of these "database change scripts", and to help manage their check in to the source code tree.

The second point is that I am only interested in source code control tools that truly track "changes" to source code files. I want to use something that knows what changed in a file, and can use this to do things like merges between different branches in a sensible way. I don't want something that just tracks the final contents of each file, and can reverse engineer what changed between two versions by working out the differences after the event. I've used Mercurial and I know that it works this way. And I'm also aware that Git works in a similar way by tracking changes to files. These are the main tools that truly track changes (there may be a few other ones as well), but it means that most other source code control tools do not track changes in the same way. Tracking changes to files is a very powerful way of doing source code control, and enables a whole bunch of advanced features around propagating changes between versions, and merging changes together.

Red Gate Source Control for Oracle

Before I tried to use the product I thought I would read up on it to understand exactly what it thought it was capable of, and how I would need to configure it to get out of it what I wanted. The first disappointment was the slightly weak product information on their web site, which was of the generic "we can do it" type without being specific about what "it" actually was that it did. But then I guess that is marketing for you.

What I did get from the product web page was that it only works with the source code control tools Subversion (SVN) or Team Foundation Server (TFS) from Microsoft. This is the first major shortcoming for this product. I'm not going to stop using Mercurial, which I find to be really good at what it does.

After that I did manage to find documentation for the product online, via the Support link on the Red Gate web site, which was good enough at describing how to use it. It seems that it will generate a set of SQL script files containing the DDL SQL statements to create the database you are using i.e. it reverse engineers from your current database the SQL that would be needed to recreate it. And having generated these SQL files it will then check them into your source code tree for you. When you change the structure of your database in any way, you can make it do a refresh and it will re-generate these SQL files, and re-upload them to your source code control tool. This means that it will update those SQL files that have changed in some way since the last source code update.

This was pretty much confirmed in a review by Lewis Cunningham, which described using Red Gate Source Control for Oracle and the series of SQL files it generated.

Which brings me to the second major shortcoming of the product - as Lewis notes "It generated create scripts rather than alters". Remember the point I made at the very start about deployed production databases must metamorphose in place, keeping the existing data inside them. This means that databases must be maintained through a series of "change scripts" that alter existing database structures to update them. We do not want just another set of "create" scripts that will create a new empty database. This is confirmed in a comment in Lewis's post by a Red Gate employee:-
I am one of the developers ... You were wondering ... how you might get the alter scripts. ... You can checkout a version of the database from SVN and Schema Compare can compare it to a live database and generate the alters you need to deploy the new version.
He is saying that Red Gate Source Code Control for Oracle will not do the "alters" for you, but Red Gate have another product called Schema Compare that will produce the "alters" for you.

Which leads on to the third shortcoming with this tool. How did my local test database get "changed" in the first place, so that Red Gate Source Control for Oracle could detect this change? If the Red Gate tool did not produce the SQL that I ran to change my local database, then it must have come from somewhere else. Most likely it came from another tool, or from SQL statements I wrote myself manually and ran against the database.

Now, if I've already got the SQL statements that "alter" the database structure, and I am sensible enough to put these into a file before running them against my local test database, then I already have the necessary "change script" that updates my database in place. And I could just check in this "change script" directly to my source code tree, and not bother with Red Gate Source Control for Oracle at all.


To summarise what Red Gate Source Control for Oracle does:
  • Red Gate Source Control for Oracle only works with SVN and TFS
  • It will not produce "alter" SQL scripts to run against a database - only "create" SQL scripts
  • You must manually or otherwise create these "alter" SQL scripts yourself to change your local database
  • It only detects changes to a database after you have already run your own "alter" SQL to change it
As a result of its limitations I didn't get around to using it because it would not work with my preferred source code control tool (Mercurial), and it would not deliver what I really needed anyway (database "change scripts").

The "holy grail" of database development tools for me would be one that helped produce the "alter" SQL statements in the first place, as a series of "change scripts". I could then test these "change scripts" locally in my test database, and if happy with the results check them into the source code tree. Unfortunately this tool from Red Gate does not do this at all, and does something completely different - only generating a complete set of "create" SQL scripts all the time, and only after you have already changed the structure of your local test database somehow.

Furthermore, I'm not sure what this tool really delivers beyond running "DBMS_METADATA.GET_DDL" (or the equivalent of it) in a loop to get the SQL DDL statements for each object in the database. I've already got my own set of scripts that do just this. The only thing Red Gate seems to add is a nice GUI in front of it all, and some integration to two source code control tools.


Richard Mitchell said...

Hi, I work on the Source Control for Oracle product and I just thought I'd mention that although the scripts folder contains CREATE scripts. The actual process of applying changes to a database uses ALTER scripts.

We effectively compare the live database schema vs. the schema in the scripts folders and migrate the changes from one to the other, without losing the data.

If you prefer more control over the ALTERs you can also use the same script folder within Schema Compare for Oracle.

Unknown said...


Are you saying that with Source Control for Oracle the tool generates ALTER scripts on the fly for each deployment, but that those ALTER scripts are available for source control?

Further, if I cannot have those alter scripts how do I package a new version upgrade deployment to n databases hosted by various customers?