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Following The Path

If you installed WebGUI 0.9.0 back in August of 2001 (the first public release), you've had a stable upgrade path through WebGUI 7.10.8 (January 2011) and beyond. Plainblack.com has been through every upgrade for the last 10 years, a shining bastion to our upgradability.

A WebGUI 7.10 user would not even recognize a WebGUI 6.0 database, much less the database used by the 1.x series, but slowly, gradually, our upgrade system brought new features to every WebGUI site that wanted them.

The Ancient Way

Our old upgrade system was quite simple:

docs/upgrade_2.9.0-3.0.0.pl
docs/upgrade_3.0.0-3.0.1.sql
docs/upgrade_3.0.0-3.0.1.pl

Our upgrade.pl script would check for docs/upgrade_*, compare version numbers, and then execute the .sql and .pl scripts in order until there were no more upgrades left.

Because each .pl script was executed individually, there was a considerable amount of boilerplate in each script (123 lines). Because there was only one script per version, some scripts could get quite long. We had conventions to manage these limitations, but it was still a bit of a mind-twist to write an upgrade routine.

Later, when we moved to simultaneous beta and stable trees, it became even more difficult to manage these huge upgrade scripts. Collecting the new features from the beta tree to apply to the stable tree was a time-consuming manual task that some poor coder had to perform, back hunched over a dimly-lit screen in the wee hours of the night, testing and re-testing the upgrade to make sure stable lived up to its expectations.

Though our upgrade system had performed admirably, it was time for a fresh look at the problem.

The Modern Vision

The individual files for upgrades was working quite well, but didn't go far enough. Our new upgrade system has one file per upgrade step. Each sub from an old upgrade script would be one file in the new upgrade system. What's more, additional file types would be supported:

$ ls share/upgrades/7.10.4-8.0.0/
addNewAdminConsole.pl
admin_console.wgpkg
facebook_auth.sql
migrateToNewCache.pl
moveMaintenance.pl
moveRequiredProfileFields.pl

So now, instead of a single file for an upgrade, we have an entire directory. In this directory, the .pl files are scripts to be run, the .wgpkg files are WebGUI assets to add to the site, the .sql files are SQL commands to run, and any .txt files will be shown as a confirmation message to the user for gotchas like "All your users have been logged out as a result of this upgrade. Deal with it.".

So now, if you want to add your own custom upgrade routine, you just add another file to the directory which means less worrying about conflicts. When we need to build another new stable version release, we can just move the unique upgrade files from beta to the new upgrade.

The best part of the new upgrade system is how the .pl scripts are written. When you are in a .pl, you have a bunch of sugar to make the basic tasks much easier.

# Old upgrade routine. Just another day in a session
sub migrateToNewCache {
    my $session = shift;
    print "\tMigrating to new cache " unless $quiet;

    use File::Path;
    rmtree "../../lib/WebGUI/Cache";
    unlink "../../lib/WebGUI/Workflow/Activity/CleanDatabaseCache.pm";
    unlink "../../lib/WebGUI/Workflow/Activity/CleanFileCache.pm";

    my $config = $session->config;
    $config->set("cache", {
        driver              => 'FastMmap',
        expires_variance   => '0.10',
        root_dir            => '/tmp/WebGUICache',
    });

    $config->set("hotSessionFlushToDb", 600);
    $config->delete("disableCache");
    $config->delete("cacheType");
    $config->delete("fileCacheRoot");
    $config->deleteFromArray("workflowActivities/None", "WebGUI::Workflow::Activity::CleanDatabaseCache");
    $config->deleteFromArray("workflowActivities/None", "WebGUI::Workflow::Activity::CleanFileCache");

    my $db = $session->db;
    $db->write("drop table cache");
    $db->write("delete from WorkflowActivity where className in ('WebGUI::Workflow::Activity::CleanDatabaseCache','WebGUI::Workflow::Activity::CleanFileCache')");
    $db->write("delete from WorkflowActivityData where activityId in  ('pbwfactivity0000000002','pbwfactivity0000000022')");

    print "DONE!\n" unless $quiet;
}

If you're familiar with WebGUI session, this is pretty standard, but still much boilerplate and convention. The new scripts remove boilerplate and enforce what was once merely convention.

# New upgrade routine. migrateToNewCache.pl
use WebGUI::Upgrade::Script;
use Module::Find;

start_step "Migrating to new cache";

rm_lib
    findallmod('WebGUI::Cache'),
    'WebGUI::Workflow::Activity::CleanDatabaseCache',
    'WebGUI::Workflow::Activity::CleanFileCache',
;

config->set("cache", {
    'driver'            => 'FastMmap',
    'expires_variance'  => '0.10',
    'root_dir'          => '/tmp/WebGUICache',
});

config->set('hotSessionFlushToDb', 600);
config->delete('disableCache');
config->delete('cacheType');
config->delete('fileCacheRoot');
config->deleteFromArray('workflowActivities/None', 'WebGUI::Workflow::Activity::CleanDatabaseCache');
config->deleteFromArray('workflowActivities/None', 'WebGUI::Workflow::Activity::CleanFileCache');

sql 'DROP TABLE IF EXISTS cache';
sql 'DELETE FROM WorkflowActivity WHERE className in (?,?)',
    'WebGUI::Workflow::Activity::CleanDatabaseCache',
    'WebGUI::Workflow::Activity::CleanFileCache',
;
sql 'DELETE FROM WorkflowActivityData WHERE activityId IN (?,?)',
    'pbwfactivity0000000002',
    'pbwfactivity0000000022',
;

done;

The first thing we do in our new upgrade script is use WebGUI::Upgrade::Script. Now, instead of using the session for everything, we have subs imported for various tasks. This means that many times we can run an entire upgrade script without opening a WebGUI session, or creating a version tag unnecessarily.

If we do need a session, or a version tag, they will be automatically assigned relevant information describing what we're doing. When we're done, they will be automatically cleaned up and committed. What once was done with boilerplate, and subject to random deletion or subversion, is now enforced policy.

In all other respects, a WebGUI upgrade script is a Perl script. You can add modules, write subroutines, and do anything necessary to move WebGUI into the future.

The Internet is always evolving. With the WebGUI 8 upgrade system, we've made it easier to evolve with it.

Stay tuned for next time where I'll show off our CHI-based caching system.