Migrating from MySQL to PostgreSQL

Note: This guide assumes you have a working GitLab instance with MySQL and want to migrate to bundled PostgreSQL database.

Omnibus installation

Prerequisites

First, we'll need to enable the bundled PostgreSQL database with up-to-date schema. Next, we'll use pgloader to migrate the data from the old MySQL database to the new PostgreSQL one.

Here's what you'll need to have installed:

  • pgloader 3.4.1+
  • Omnibus GitLab
  • MySQL

Enable bundled PostgreSQL database

  1. Stop GitLab:

    sudo gitlab-ctl stop
    
  2. Edit /etc/gitlab/gitlab.rb to enable bundled PostgreSQL:

    postgresql['enable'] = true
    
  3. Edit /etc/gitlab/gitlab.rb to use the bundled PostgreSQL. Please check all the settings beginning with db_, such as gitlab_rails['db_adapter'] and alike. You could just comment all of them out so that we'll just use the defaults.

  4. Reconfigure GitLab for the changes to take effect:

    sudo gitlab-ctl reconfigure
    
  5. Start Unicorn and PostgreSQL so that we can prepare the schema:

    sudo gitlab-ctl start unicorn
    sudo gitlab-ctl start postgresql
    
  6. Run the following commands to prepare the schema:

    sudo gitlab-rake db:create db:migrate
    
  7. Stop Unicorn to prevent other database access from interfering with the loading of data:

    sudo gitlab-ctl stop unicorn
    

After these steps, you'll have a fresh PostgreSQL database with up-to-date schema.

Migrate data from MySQL to PostgreSQL

Now, you can use pgloader to migrate the data from MySQL to PostgreSQL:

  1. Save the following snippet in a commands.load file, and edit with your database username, password and host:

    LOAD DATABASE
         FROM mysql://username:password@host/gitlabhq_production
         INTO postgresql://gitlab-psql@unix://var/opt/gitlab/postgresql:/gitlabhq_production
    
    WITH include no drop, truncate, disable triggers, create no tables,
         create no indexes, preserve index names, no foreign keys,
         data only
    
    ALTER SCHEMA 'gitlabhq_production' RENAME TO 'public'
    
    ;
    
  2. Start the migration:

    sudo -u gitlab-psql pgloader commands.load
    
  3. Once the migration finishes, you should see a summary table that looks like the following:

                                     table name       read   imported     errors      total time
    -----------------------------------------------  ---------  ---------  ---------  --------------
                                    fetch meta data        119        119          0          0.388s
                                           Truncate        119        119          0          1.134s
    -----------------------------------------------  ---------  ---------  ---------  --------------
                               public.abuse_reports          0          0          0          0.490s
                                 public.appearances          0          0          0          0.488s
                                           .
                                           .
                                           .
                               public.web_hook_logs          0          0          0          1.080s
    -----------------------------------------------  ---------  ---------  ---------  --------------
                            COPY Threads Completion          4          4          0          2.008s
                                    Reset Sequences        113        113          0          0.304s
                                   Install Comments          0          0          0          0.000s
    -----------------------------------------------  ---------  ---------  ---------  --------------
                                  Total import time       1894       1894          0         12.497s
    

    If there is no output for more than 30 minutes, it's possible pgloader encountered an error. See the troubleshooting guide for more details.

  4. Start GitLab:

    sudo gitlab-ctl start
    

Now, you can verify that everything worked by visiting GitLab.

Troubleshooting

Permissions

Note that the PostgreSQL user that you use for the above MUST have superuser privileges. Otherwise, you may see a similar message to the following:

debugger invoked on a CL-POSTGRES-ERROR:INSUFFICIENT-PRIVILEGE in thread
    #<THREAD "lparallel" RUNNING {10078A3513}>:
      Database error 42501: permission denied: "RI_ConstraintTrigger_a_20937" is a system trigger
    QUERY: ALTER TABLE ci_builds DISABLE TRIGGER ALL;
    2017-08-23T00:36:56.782000Z ERROR Database error 42501: permission denied: "RI_ConstraintTrigger_c_20864" is a system trigger
    QUERY: ALTER TABLE approver_groups DISABLE TRIGGER ALL;

Experiencing 500 errors after the migration

If you experience 500 errors after the migration, try to clear the cache:

sudo gitlab-rake cache:clear

Source installation

Prerequisites

Install PostgreSQL and create database

See installation guide.

Install pgloader 3.4.1+

Install directly from your distro:

sudo apt-get install pgloader

If this version is too old, use PostgreSQL's repository:

# add repository
sudo sh -c 'echo "deb http://apt.postgresql.org/pub/repos/apt/ $(lsb_release -cs)-pgdg main" > /etc/apt/sources.list.d/pgdg.list'

# add key
sudo apt-get install wget ca-certificates
wget --quiet -O - https://www.postgresql.org/media/keys/ACCC4CF8.asc | sudo apt-key add -

# install package
sudo apt-get update
sudo apt-get install pgloader

Enable bundled PostgreSQL database

  1. Stop GitLab:

    sudo service gitlab stop
    
  2. Switch database from MySQL to PostgreSQL

   cd /home/git/gitlab
   sudo -u git mv config/database.yml config/database.yml.bak
   sudo -u git cp config/database.yml.postgresql config/database.yml
   sudo -u git -H chmod o-rwx config/database.yml
  1. Run the following commands to prepare the schema:

    sudo -u git -H bundle exec rake db:create db:migrate RAILS_ENV=production
    

After these steps, you'll have a fresh PostgreSQL database with up-to-date schema.

Migrate data from MySQL to PostgreSQL

Now, you can use pgloader to migrate the data from MySQL to PostgreSQL:

  1. Save the following snippet in a commands.load file, and edit with your MySQL username, password and host:

    LOAD DATABASE
         FROM mysql://username:password@host/gitlabhq_production
         INTO postgresql://postgres@unix://var/run/postgresql:/gitlabhq_production
    
    WITH include no drop, truncate, disable triggers, create no tables,
         create no indexes, preserve index names, no foreign keys,
         data only
    
    ALTER SCHEMA 'gitlabhq_production' RENAME TO 'public'
    
    ;
    
  2. Start the migration:

    sudo -u postgres pgloader commands.load
    
  3. Once the migration finishes, you should see a summary table that looks like the following:

                                     table name       read   imported     errors      total time
    -----------------------------------------------  ---------  ---------  ---------  --------------
                                    fetch meta data        119        119          0          0.388s
                                           Truncate        119        119          0          1.134s
    -----------------------------------------------  ---------  ---------  ---------  --------------
                               public.abuse_reports          0          0          0          0.490s
                                 public.appearances          0          0          0          0.488s
                                           .
                                           .
                                           .
                               public.web_hook_logs          0          0          0          1.080s
    -----------------------------------------------  ---------  ---------  ---------  --------------
                            COPY Threads Completion          4          4          0          2.008s
                                    Reset Sequences        113        113          0          0.304s
                                   Install Comments          0          0          0          0.000s
    -----------------------------------------------  ---------  ---------  ---------  --------------
                                  Total import time       1894       1894          0         12.497s
    

    If there is no output for more than 30 minutes, it's possible pgloader encountered an error. See the troubleshooting guide for more details.

  4. Start GitLab:

    sudo service gitlab start
    

Now, you can verify that everything worked by visiting GitLab.

Troubleshooting

Experiencing 500 errors after the migration

If you experience 500 errors after the migration, try to clear the cache:

sudo -u git -H bundle exec rake cache:clear RAILS_ENV=production