DDevelopment & Design

Use XMLs not groovy scripts with db migration plugin!

I have 48 domain classes in my Grails 2.1 project and I use Grails Database Migration Plugin 1.2 for a database management. Recently I’ve noticed that it becomes terribly slow when running application, even if there are no changes to be applied. I swit…

I have 48 domain classes in my Grails 2.1 project and I use Grails Database Migration Plugin 1.2 for a database management. Recently I’ve noticed that it becomes terribly slow when running application, even if there are no changes to be applied.

I switched do debug logging level for liquibase package and I found that it takes about 15 seconds to parse changelog.groovy and 20 files that were included in it!

Prepare benchmark

I couldn’t belive it so I’ve created two new clean changelogs:

$ grails dbm-generate-changelog changelog.groovy
$ grails dbm-generate-changelog changelog.xml

Both of these changelogs contain 229 change sets. It is enough that you can benchmark parsers for them. Two parsers in question are:

  • grails.plugin.databasemigration.GrailsChangeLogParser
  • liquibase.parser.core.xml.XMLChangeLogSAXParser

I need to modify a line in my Config.groovy and switch changelog.groovy with changelog.xml for a second test:

grails.plugin.databasemigration.updateOnStart = true
grails.plugin.databasemigration.updateOnStartFileNames = ["changelog.groovy"]
// grails.plugin.databasemigration.updateOnStartFileNames = ["changelog.xml"] grails.plugin.databasemigration.updateOnStart = true
grails.plugin.databasemigration.updateOnStartFileNames = ["changelog-all.groovy"]
// grails.plugin.databasemigration.updateOnStartFileNames = ["changelog-all.xml"]

Profile with JProfiler

I want to profile execution time. I use JProfiler from ej-technologies to measure execution times. Please notice that I don’t want to benchmark SQL queries performed by liquibase. I am only focused on parse method of these two classes.

Here’s how I set up JProfiler:

I switch to CPU Views – Method statistics and I click “Record”. Here are results for both parsers:

Results for changelog.groovy

Results for changelog.xml

Analysis

My assumptions were correct: 8 339 ms vs 139 ms. Parsing XML is 60 times faster! I want to jump and sing: “I switch to XML now!”, but I have some concerns. I have a production database that I need to be compatible with. And I should rewrite my all groovy changelog files by hand. So it’s not so trivial and it’s a time consuming and error prone task.

So as much as I want to switch to XML now, I won’t. But if you start your adventure with database migration plugin today I have an advice for you: use XML if you start from scratch.

For now I’ve just submitted a new JIRA issue – GrailsChangeLogParser – parse method is very slow and I hope it can be greatly improved.

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DDevelopment & Design

Private fields and methods are not private in groovy

I used to code in Java before I met groovy. Like most of you, groovy attracted me with many enhancements. This was to my surprise to discover that method visibility in groovy is handled different than Java!

Consider this example:

class Person {
private String name
public  String surname

private Person() {}

private String signature() { "${name?.substring(0, 1)}. $surname" }

public String toString() { "I am $name $surname" }
}

How is this class interpreted with Java?

  1. Person has private constructor that cannot be accessed
  2. Field "name" is private and cannot be accessed
  3. Method signature() is private and cannot be accessed

Let's see how groovy interpretes Person:

public static void main(String[] args) {
def person = new Person()   // constructor is private - compilation error in Java
println(person.toString())

    person.@name = 'Mike'       // access name field directly - compilation error in Java
println(person.toString())

    person.name = 'John'        // there is a setter generated by groovy
println(person.toString())

    person.@surname = 'Foo'     // access surname field directly
println(person.toString())

    person.surname = 'Bar'      // access auto-generated setter
println(person.toString())

println(person.signature()) // call private method - compilation error in Java
}

I was really astonished by its output:

I am null null
I am Mike null
I am John null
I am John Foo
I am John Bar
J. Bar

As you can see, groovy does not follow visibility directives at all! It treats them as non-existing. Code compiles and executes fine. It's contrary to Java. In Java this code has several errors, pointed out in comments.

I've searched a bit on this topic and it seems that this behaviour is known since version 1.1 and there is a bug report on that: http://jira.codehaus.org/browse/GROOVY-1875. It is not resolved even with groovy 2 release. As Tim Yates mentioned in this Stackoverflow question: "It's not clear if it is a bug or by design". Groovy treats visibility keywords as a hint for a programmer.

I need to keep that lesson in mind next time I want to make some field or method private!