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stage: Verify
group: Pipeline Execution
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# Merged results pipelines **(PREMIUM)**

> [Renamed](https://gitlab.com/gitlab-org/gitlab/-/issues/351192) from `pipelines for merged results` to `merged results pipelines` in GitLab 14.8.

A *merged results pipeline* is a type of [merge request pipeline](merge_request_pipelines.md). It is a pipeline that runs against the results of the source and target branches merged together.

GitLab creates an internal commit with the merged results, so the pipeline can run
against it. This commit does not exist in either branch,
but you can view it in the pipeline details.

The pipeline runs against the target branch as it exists at the moment you run the pipeline.
Over time, while you're working in the source branch, the target branch might change.
Any time you want to be sure the merged results are accurate, you should re-run the pipeline.

Merged results pipelines can't run when:

- The target branch has changes that conflict with the changes in the source branch.
- The merge request is a [**Draft** merge request](../../user/project/merge_requests/drafts.md).

In these cases, the pipeline runs as a [merge request pipeline](merge_request_pipelines.md)
and is labeled as `detached`.

## Prerequisites

To use merged results pipelines:

- Your project's [CI/CD configuration file](../yaml/index.md) must be configured to
  [run jobs in merge request pipelines](merge_request_pipelines.md#prerequisites).
- Your repository must be a GitLab repository, not an
  [external repository](../ci_cd_for_external_repos/index.md).
- You must not be using [fast forward merges](../../user/project/merge_requests/fast_forward_merge.md).
  [An issue exits](https://gitlab.com/gitlab-org/gitlab/-/issues/26996) to change this behavior.

## Enable merged results pipelines

To enable merged results pipelines in a project, you must have at least the
Maintainer role:

1. On the top bar, select **Menu > Projects** and find your project.
1. On the left sidebar, select **Settings > General**.
1. Expand **Merge requests**.
1. Select **Enable merged results pipelines**.
1. Select **Save changes**.

WARNING:
If you select the checkbox but don't configure your pipeline to use
merge request pipelines, your merge requests may become stuck in an
unresolved state or your pipelines may be dropped.

## Troubleshooting

### Merged results pipelines are not created

In GitLab 13.7 and earlier, merged results pipelines might not be created due
to a disabled [feature flag](../../user/feature_flags.md). This feature flag
[was removed](https://gitlab.com/gitlab-org/gitlab/-/issues/299115) in GitLab 13.8.
Upgrade to 13.8 or later, or make sure the `:merge_ref_auto_sync`
[feature flag is enabled](../../administration/feature_flags.md#check-if-a-feature-flag-is-enabled)
on your GitLab instance.

### Pipelines fail intermittently with a `fatal: reference is not a tree:` error

Merged results pipelines run on a merge ref for a merge request
(`refs/merge-requests/<iid>/merge`), so the Git reference could be overwritten at an
unexpected time.

For example, when a source or target branch is advanced, the pipeline fails with
the `fatal: reference is not a tree:` error, which indicates that the checkout-SHA
is not found in the merge ref.

This behavior was improved in GitLab 12.4 by introducing [persistent pipeline refs](../troubleshooting.md#fatal-reference-is-not-a-tree-error).
Upgrade to GitLab 12.4 or later to resolve the problem.
