@title Diffusion User Guide: Repository Updates
@group userguide

Explains how Diffusion updates repositories to discover new changes.

Overview
========

When Phabricator is configured to import repositories which are hosted
elsewhere, it needs to poll those repositories for changes. If it polls too
frequently, it can create too much load locally and on remote services. If it
polls too rarely, it may take a long time for commits to show up in the web
interface.

This document describes the rules around polling and how to understand and
adjust the behavior. In general:

  - Phabricator chooses a default poll interval based on repository
    activity. These intervals range from every 15 seconds (for active
    repositories) to every 6 hours (for repositories with no commits in two
    months).
  - If you use `arc` to push commits, or you host repositories on Phabricator,
    repositories automatically update after changes are pushed.
  - If you don't use `arc` and your repository is hosted elsewhere, this
    document describes ways you can make polling more responsive.


Default Behavior
================

By default, Phabricator determines how frequently to poll repositories by
examining how long it has been since the last commit. In most cases this is
fairly accurate and produces good behavior. In particular, it automatically
reduces the polling frequency for rarely-used repositories. This dramatically
reduces load for installs with a large number of inactive repositories, which
is common.

For repositories with activity in the last 3 days, we wait 1 second for every
10 minutes without activity. The table below has some examples.

| Time Since Commit | Poll Interval    |
|-------------------|------------------|
| //Minimum//       | 15 seconds       |
| 6h                | about 30 seconds |
| 12h               | about 1 minute   |
| 1 day             | about 2 minutes  |
| 2 days            | about 5 minutes  |
| 3 days            | about 7 minutes  |

This means that you may need to wait about 2 minutes for the first commit to
be imported in the morning, and about 5 minutes after a long weekend, but other
commits to active repositories should usually be recognized in 30 seconds or
less.

For repositories with no activity in the last 3 days, we wait longer between
updates (1 second for every 4 minutes without activity). The table below has
some examples.

| Time Since Commit | Poll Interval    |
|-------------------|------------------|
| 4 days            | about 30 minutes |
| 7 days            | about 45 minutes |
| 10 days           | about 1 hour     |
| 20 days           | about 2 hours    |
| 30 days           | about 3 hours    |
| //Maximum//       | 6 hours          |

You can find the exact default poll frequency of a repository in
Diffusion > (Choose a Repository) > Edit Repository, under "Update Frequency".
You can also see the time when the repository was last updated in this
interface.

Repositories that are currently importing are always updated at the minimum
update frequency so the import finishes as quickly as possible.


Triggering Repository Updates
=============================

If you want Phabricator to update a repository more quickly than the default
update frequency (for example, because you just pushed a commit to it), you can
tell Phabricator that it should schedule an update as soon as possible.

There are several ways to do this:

  - If you push changes with `arc land` or `arc commit`, this will be done
    for you automatically. These commits should normally be recognized within
    a few seconds.
  - If your repository is hosted on Phabricator, this will also be done for you
    automatically.
  - You can schedule an update from the web interface, in Diffusion >
    (Choose a Repository) > Edit Repository > Update Now.
  - You can make a call to the Conduit API method `diffusion.looksoon`. This
    hints to Phabricator that it should poll a repository as soon as it can.
    All of the other mechanisms do this under the hood.

In particular, you may be able to add a commit hook to your external repository
which calls `diffusion.looksoon`. This should make an external repository about
as responsive as a hosted repository.

If a repository has an update scheduled, the Diffusion > (Choose a
Repository) > Edit Repository interface will show that the the repository is
prioritized and will be updated soon.


Troubleshooting Updates
=======================

You can manually run a repository update from the command line to troubleshoot
issues, using the `--trace` flag to get full details:

  phabricator/ $ ./bin/repository update --trace <callsign>

To catch potential issues with permissions, run this command as the same user
that the daemons run as.
