115 lines
4.5 KiB
Markdown
115 lines
4.5 KiB
Markdown
# Working with Merge Request diffs
|
|
|
|
Currently we rely on different sources to present merge request diffs, these include:
|
|
|
|
- Rugged gem
|
|
- Gitaly service
|
|
- Database (through `merge_request_diff_files`)
|
|
- Redis (cached highlighted diffs)
|
|
|
|
We're constantly moving Rugged calls to Gitaly and the progress can be followed through [Gitaly repo](https://gitlab.com/gitlab-org/gitaly).
|
|
|
|
## Architecture overview
|
|
|
|
When refreshing a Merge Request (pushing to a source branch, force-pushing to target branch, or if the target branch now contains any commits from the MR)
|
|
we fetch the comparison information using `Gitlab::Git::Compare`, which fetches `base` and `head` data using Gitaly and diff between them through
|
|
`Gitlab::Git::Diff.between` (which uses _Gitaly_ if it's enabled, otherwise _Rugged_).
|
|
The diffs fetching process _limits_ single file diff sizes and the overall size of the whole diff through a series of constant values. Raw diff files are
|
|
then persisted on `merge_request_diff_files` table.
|
|
|
|
Even though diffs higher than 10kb are collapsed (`Gitlab::Git::Diff::COLLAPSE_LIMIT`), we still keep them on Postgres. However, diff files over _safety limits_
|
|
(see the [Diff limits section](#diff-limits)) are _not_ persisted.
|
|
|
|
In order to present diffs information on the Merge Request diffs page, we:
|
|
|
|
1. Fetch all diff files from database `merge_request_diff_files`
|
|
2. Fetch the _old_ and _new_ file blobs in batch to:
|
|
1. Highlight old and new file content
|
|
2. Know which viewer it should use for each file (text, image, deleted, etc)
|
|
3. Know if the file content changed
|
|
4. Know if it was stored externally
|
|
5. Know if it had storage errors
|
|
3. If the diff file is cacheable (text-based), it's cached on Redis
|
|
using `Gitlab::Diff::FileCollection::MergeRequestDiff`
|
|
|
|
## Diff limits
|
|
|
|
As explained above, we limit single diff files and the size of the whole diff. There are scenarios where we collapse the diff file,
|
|
and cases where the diff file is not presented at all, and the user is guided to the Blob view. Here we'll go into details about
|
|
these limits.
|
|
|
|
### Diff collection limits
|
|
|
|
Limits that act onto all diff files collection. Files number, lines number and files size are considered.
|
|
|
|
```ruby
|
|
Gitlab::Git::DiffCollection.collection_limits[:safe_max_files] = Gitlab::Git::DiffCollection::DEFAULT_LIMITS[:max_files] = 100
|
|
```
|
|
|
|
File diffs will be collapsed (but be expandable) if 100 files have already been rendered.
|
|
|
|
|
|
```ruby
|
|
Gitlab::Git::DiffCollection.collection_limits[:safe_max_lines] = Gitlab::Git::DiffCollection::DEFAULT_LIMITS[:max_lines] = 5000
|
|
```
|
|
|
|
File diffs will be collapsed (but be expandable) if 5000 lines have already been rendered.
|
|
|
|
|
|
```ruby
|
|
Gitlab::Git::DiffCollection.collection_limits[:safe_max_bytes] = Gitlab::Git::DiffCollection.collection_limits[:safe_max_files] * 5.kilobytes = 500.kilobytes
|
|
```
|
|
|
|
File diffs will be collapsed (but be expandable) if 500 kilobytes have already been rendered.
|
|
|
|
|
|
```ruby
|
|
Gitlab::Git::DiffCollection.collection_limits[:max_files] = Commit::DIFF_HARD_LIMIT_FILES = 1000
|
|
```
|
|
|
|
No more files will be rendered at all if 1000 files have already been rendered.
|
|
|
|
|
|
```ruby
|
|
Gitlab::Git::DiffCollection.collection_limits[:max_lines] = Commit::DIFF_HARD_LIMIT_LINES = 50000
|
|
```
|
|
|
|
No more files will be rendered at all if 50,000 lines have already been rendered.
|
|
|
|
```ruby
|
|
Gitlab::Git::DiffCollection.collection_limits[:max_bytes] = Gitlab::Git::DiffCollection.collection_limits[:max_files] * 5.kilobytes = 5000.kilobytes
|
|
```
|
|
|
|
No more files will be rendered at all if 5 megabytes have already been rendered.
|
|
|
|
|
|
### Individual diff file limits
|
|
|
|
Limits that act onto each diff file of a collection. Files number, lines number and files size are considered.
|
|
|
|
```ruby
|
|
Gitlab::Git::Diff::COLLAPSE_LIMIT = 10.kilobytes
|
|
```
|
|
|
|
File diff will be collapsed (but be expandable) if it is larger than 10 kilobytes.
|
|
|
|
```ruby
|
|
Gitlab::Git::Diff::SIZE_LIMIT = 100.kilobytes
|
|
```
|
|
|
|
File diff will not be rendered if it's larger than 100 kilobytes.
|
|
|
|
|
|
```ruby
|
|
Commit::DIFF_SAFE_LINES = Gitlab::Git::DiffCollection::DEFAULT_LIMITS[:max_lines] = 5000
|
|
```
|
|
|
|
File diff will be suppressed (technically different from collapsed, but behaves the same, and is expandable) if it has more than 5000 lines.
|
|
|
|
## Viewers
|
|
|
|
Diff Viewers, which can be found on `models/diff_viewer/*` are classes used to map metadata about each type of Diff File. It has information
|
|
whether it's a binary, which partial should be used to render it or which File extensions this class accounts for.
|
|
|
|
`DiffViewer::Base` validates _blobs_ (old and new versions) content, extension and file type in order to check if it can be rendered.
|
|
|