# Code import in depth Launchpad has the ability to constantly sync code from external repositories by setting up a code import. This is a one-way sync, from the external source to Launchpad. ## Design decisions Code import / code mirroring is not triggered by the remote repository, but it is rather triggered from the Launchpad side several times a day. This should be fine for most use cases. The benefit of doing it this way is there is no need to install a webhook on the remote repository to trigger an import or update of the repository. ## Frequency While the current implementation has some support for setting it on a per-import basis, that’s actually not exposed right now. The frequency depends on the type of the revision control system, and is set in `effective_update_interval`, see [the codeimport module](https://git.launchpad.net/launchpad/tree/lib/lp/code/model/codeimport.py). As the default intervals in the config schema aren’t overridden anywhere right now, you can look them up in the `codeimport` section in the [configuration schema](https://git.launchpad.net/launchpad/tree/lib/lp/services/config/schema-lazr.conf). ## Trigger code import On a high level, each import has a database field, which indicates when the next import should be performed. We could think of this as task queue. A scheduler queries the database, and in case there are jobs, a worker will pick one up. Let’s have a look in detail. After the import job runs, and if the import is still in the `REVIEWED` state, i.e. it hasn’t failed too many times, or it hasn’t been suspended or similar, it then schedules a new job, that is, it sets a new date in the `date_due` column. Depending on the work load, there is no guarantee that a job will be picked up in time, as the process works like this: - cronjobs in `lp-codeimport` run workers - when the code import worker is looking for work to do, it calls `getJobForMachine` in the [codeimportscheduler module](https://git.launchpad.net/launchpad/tree/lib/lp/code/xmlrpc/codeimportscheduler.py) - that calls `getJobForMachine` in the [codeimport module](https://git.launchpad.net/launchpad/tree/lib/lp/code/model/codeimportjob.py) which makes a DB query to fetch the first job from a table that has `due_date` not in the future, and that is marked as `pending` - it then triggers the import ## Conclusion The short answer is that we currently aim for every 12 hours for code imports from CVS (very few nowadays), and every 6 hours from all other revision control systems.