248 lines
11 KiB
Markdown
248 lines
11 KiB
Markdown
# Value Stream Analytics development guide
|
||
|
||
Value stream analytics calculates the time between two arbitrary events recorded on domain objects and provides aggregated statistics about the duration.
|
||
|
||
For information on how to configure Value Stream Analytics in GitLab, see our [analytics documentation](../user/analytics/value_stream_analytics.md).
|
||
|
||
## Stage
|
||
|
||
During development, events occur that move issues and merge requests through different stages of progress until they are considered finished. These stages can be expressed with the `Stage` model.
|
||
|
||
Example stage:
|
||
|
||
- Name: Development
|
||
- Start event: Issue created
|
||
- End event: Issue first mentioned in commit
|
||
- Parent: `Group: gitlab-org`
|
||
|
||
### Events
|
||
|
||
Events are the smallest building blocks of the value stream analytics feature. A stage consists of two events:
|
||
|
||
- Start
|
||
- End
|
||
|
||
These events play a key role in the duration calculation.
|
||
|
||
Formula: `duration = end_event_time - start_event_time`
|
||
|
||
To make the duration calculation flexible, each `Event` is implemented as a separate class. They're responsible for defining a timestamp expression that will be used in the calculation query.
|
||
|
||
#### Implementing an `Event` class
|
||
|
||
There are a few methods that are required to be implemented, the `StageEvent` base class describes them in great detail. The most important ones are:
|
||
|
||
- `object_type`
|
||
- `timestamp_projection`
|
||
|
||
The `object_type` method defines which domain object will be queried for the calculation. Currently two models are allowed:
|
||
|
||
- `Issue`
|
||
- `MergeRequest`
|
||
|
||
For the duration calculation the `timestamp_projection` method will be used.
|
||
|
||
```ruby
|
||
def timestamp_projection
|
||
# your timestamp expression comes here
|
||
end
|
||
|
||
# event will use the issue creation time in the duration calculation
|
||
def timestamp_projection
|
||
Issue.arel_table[:created_at]
|
||
end
|
||
```
|
||
|
||
NOTE: **Note:**
|
||
More complex expressions are also possible (e.g. using `COALESCE`). Look at the existing event classes for examples.
|
||
|
||
In some cases, defining the `timestamp_projection` method is not enough. The calculation query should know which table contains the timestamp expression. Each `Event` class is responsible for making modifications to the calculation query to make the `timestamp_projection` work. This usually means joining an additional table.
|
||
|
||
Example for joining the `issue_metrics` table and using the `first_mentioned_in_commit_at` column as the timestamp expression:
|
||
|
||
```ruby
|
||
def object_type
|
||
Issue
|
||
end
|
||
|
||
def timestamp_projection
|
||
IssueMetrics.arel_table[:first_mentioned_in_commit_at]
|
||
end
|
||
|
||
def apply_query_customization(query)
|
||
# in this case the query attribute will be based on the Issue model: `Issue.where(...)`
|
||
query.joins(:metrics)
|
||
end
|
||
```
|
||
|
||
### Validating start and end events
|
||
|
||
Some start/end event pairs are not "compatible" with each other. For example:
|
||
|
||
- "Issue created" to "Merge Request created": The event classes are defined on different domain models, the `object_type` method is different.
|
||
- "Issue closed" to "Issue created": Issue must be created first before it can be closed.
|
||
- "Issue closed" to "Issue closed": Duration is always 0.
|
||
|
||
The `StageEvents` module describes the allowed `start_event` and `end_event` pairings (`PAIRING_RULES` constant). If a new event is added, it needs to be registered in this module.
|
||
To add a new event:
|
||
|
||
1. Add an entry in `ENUM_MAPPING` with a unique number, it'll be used in the `Stage` model as `enum`.
|
||
1. Define which events are compatible with the event in the `PAIRING_RULES` hash.
|
||
|
||
Supported start/end event pairings:
|
||
|
||
```mermaid
|
||
graph LR;
|
||
IssueCreated --> IssueClosed;
|
||
IssueCreated --> IssueFirstAddedToBoard;
|
||
IssueCreated --> IssueFirstAssociatedWithMilestone;
|
||
IssueCreated --> IssueFirstMentionedInCommit;
|
||
IssueCreated --> IssueLastEdited;
|
||
IssueCreated --> IssueLabelAdded;
|
||
IssueCreated --> IssueLabelRemoved;
|
||
MergeRequestCreated --> MergeRequestMerged;
|
||
MergeRequestCreated --> MergeRequestClosed;
|
||
MergeRequestCreated --> MergeRequestFirstDeployedToProduction;
|
||
MergeRequestCreated --> MergeRequestLastBuildStarted;
|
||
MergeRequestCreated --> MergeRequestLastBuildFinished;
|
||
MergeRequestCreated --> MergeRequestLastEdited;
|
||
MergeRequestCreated --> MergeRequestLabelAdded;
|
||
MergeRequestCreated --> MergeRequestLabelRemoved;
|
||
MergeRequestLastBuildStarted --> MergeRequestLastBuildFinished;
|
||
MergeRequestLastBuildStarted --> MergeRequestClosed;
|
||
MergeRequestLastBuildStarted --> MergeRequestFirstDeployedToProduction;
|
||
MergeRequestLastBuildStarted --> MergeRequestLastEdited;
|
||
MergeRequestLastBuildStarted --> MergeRequestMerged;
|
||
MergeRequestLastBuildStarted --> MergeRequestLabelAdded;
|
||
MergeRequestLastBuildStarted --> MergeRequestLabelRemoved;
|
||
MergeRequestMerged --> MergeRequestFirstDeployedToProduction;
|
||
MergeRequestMerged --> MergeRequestClosed;
|
||
MergeRequestMerged --> MergeRequestFirstDeployedToProduction;
|
||
MergeRequestMerged --> MergeRequestLastEdited;
|
||
MergeRequestMerged --> MergeRequestLabelAdded;
|
||
MergeRequestMerged --> MergeRequestLabelRemoved;
|
||
IssueLabelAdded --> IssueLabelAdded;
|
||
IssueLabelAdded --> IssueLabelRemoved;
|
||
IssueLabelAdded --> IssueClosed;
|
||
IssueLabelRemoved --> IssueClosed;
|
||
IssueFirstAddedToBoard --> IssueClosed;
|
||
IssueFirstAddedToBoard --> IssueFirstAssociatedWithMilestone;
|
||
IssueFirstAddedToBoard --> IssueFirstMentionedInCommit;
|
||
IssueFirstAddedToBoard --> IssueLastEdited;
|
||
IssueFirstAddedToBoard --> IssueLabelAdded;
|
||
IssueFirstAddedToBoard --> IssueLabelRemoved;
|
||
IssueFirstAssociatedWithMilestone --> IssueClosed;
|
||
IssueFirstAssociatedWithMilestone --> IssueFirstAddedToBoard;
|
||
IssueFirstAssociatedWithMilestone --> IssueFirstMentionedInCommit;
|
||
IssueFirstAssociatedWithMilestone --> IssueLastEdited;
|
||
IssueFirstAssociatedWithMilestone --> IssueLabelAdded;
|
||
IssueFirstAssociatedWithMilestone --> IssueLabelRemoved;
|
||
IssueFirstMentionedInCommit --> IssueClosed;
|
||
IssueFirstMentionedInCommit --> IssueFirstAssociatedWithMilestone;
|
||
IssueFirstMentionedInCommit --> IssueFirstAddedToBoard;
|
||
IssueFirstMentionedInCommit --> IssueLastEdited;
|
||
IssueFirstMentionedInCommit --> IssueLabelAdded;
|
||
IssueFirstMentionedInCommit --> IssueLabelRemoved;
|
||
IssueClosed --> IssueLastEdited;
|
||
IssueClosed --> IssueLabelAdded;
|
||
IssueClosed --> IssueLabelRemoved;
|
||
MergeRequestClosed --> MergeRequestFirstDeployedToProduction;
|
||
MergeRequestClosed --> MergeRequestLastEdited;
|
||
MergeRequestClosed --> MergeRequestLabelAdded;
|
||
MergeRequestClosed --> MergeRequestLabelRemoved;
|
||
MergeRequestFirstDeployedToProduction --> MergeRequestLastEdited;
|
||
MergeRequestFirstDeployedToProduction --> MergeRequestLabelAdded;
|
||
MergeRequestFirstDeployedToProduction --> MergeRequestLabelRemoved;
|
||
MergeRequestLastBuildFinished --> MergeRequestClosed;
|
||
MergeRequestLastBuildFinished --> MergeRequestFirstDeployedToProduction;
|
||
MergeRequestLastBuildFinished --> MergeRequestLastEdited;
|
||
MergeRequestLastBuildFinished --> MergeRequestMerged;
|
||
MergeRequestLastBuildFinished --> MergeRequestLabelAdded;
|
||
MergeRequestLastBuildFinished --> MergeRequestLabelRemoved;
|
||
MergeRequestLabelAdded --> MergeRequestLabelAdded;
|
||
MergeRequestLabelAdded --> MergeRequestLabelRemoved;
|
||
MergeRequestLabelRemoved --> MergeRequestLabelAdded;
|
||
MergeRequestLabelRemoved --> MergeRequestLabelRemoved;
|
||
```
|
||
|
||
### Parent
|
||
|
||
Teams and organizations might define their own way of building software, thus stages can be completely different. For each stage, a parent object needs to be defined.
|
||
|
||
Currently supported parents:
|
||
|
||
- `Project`
|
||
- `Group`
|
||
|
||
#### How parent relationship it work
|
||
|
||
1. User navigates to the value stream analytics page.
|
||
1. User selects a group.
|
||
1. Backend loads the defined stages for the selected group.
|
||
1. Additions and modifications to the stages will be persisted within the selected group only.
|
||
|
||
### Default stages
|
||
|
||
The [original implementation](https://gitlab.com/gitlab-org/gitlab/issues/847) of value stream analytics defined 7 stages. These stages are always available for each parent, however altering these stages is not possible.
|
||
|
||
To make things efficient and reduce the number of records created, the default stages are expressed as in-memory objects (not persisted). When the user creates a custom stage for the first time, all the stages will be persisted. This behaviour is implemented in the value stream analytics service objects.
|
||
|
||
The reason for this was that we'd like to add the abilities to hide and order stages later on.
|
||
|
||
## Data Collector
|
||
|
||
`DataCollector` is the central point where the data will be queried from the database. The class always operates on a single stage and consists of the following components:
|
||
|
||
- `BaseQueryBuilder`:
|
||
- Responsible for composing the initial query.
|
||
- Deals with `Stage` specific configuration: events and their query customizations.
|
||
- Parameters coming from the UI: date ranges.
|
||
- `Median`: Calculates the median duration for a stage using the query from `BaseQueryBuilder`.
|
||
- `RecordsFetcher`: Loads relevant records for a stage using the query from `BaseQueryBuilder` and specific `Finder` classes to apply visibility rules.
|
||
- `DataForDurationChart`: Loads calculated durations with the finish time (end event timestamp) for the scatterplot chart.
|
||
|
||
For a new calculation or a query, implement it as a new method call in the `DataCollector` class.
|
||
|
||
## Database query
|
||
|
||
Structure of the database query:
|
||
|
||
```sql
|
||
SELECT (customized by: Median or RecordsFetcher or DataForDurationChart)
|
||
FROM OBJECT_TYPE (Issue or MergeRequest)
|
||
INNER JOIN (several JOIN statements, depending on the events)
|
||
WHERE
|
||
(Filter by the PARENT model, example: filter Issues from Project A)
|
||
(Date range filter based on the OBJECT_TYPE.created_at)
|
||
(Check if the START_EVENT is earlier than END_EVENT, preventing negative duration)
|
||
```
|
||
|
||
Structure of the `SELECT` statement for `Median`:
|
||
|
||
```sql
|
||
SELECT (calculate median from START_EVENT_TIME-END_EVENT_TIME)
|
||
```
|
||
|
||
Structure of the `SELECT` statement for `DataForDurationChart`:
|
||
|
||
```sql
|
||
SELECT (START_EVENT_TIME-END_EVENT_TIME) as duration, END_EVENT.timestamp
|
||
```
|
||
|
||
## High-level overview
|
||
|
||
- Rails Controller (`Analytics::CycleAnalytics` module): Value stream analytics exposes its data via JSON endpoints, implemented within the `analytics` workspace. Configuring the stages are also implements JSON endpoints (CRUD).
|
||
- Services (`Analytics::CycleAnalytics` module): All `Stage` related actions will be delegated to respective service objects.
|
||
- Models (`Analytics::CycleAnalytics` module): Models are used to persist the `Stage` objects `ProjectStage` and `GroupStage`.
|
||
- Feature classes (`Gitlab::Analytics::CycleAnalytics` module):
|
||
- Responsible for composing queries and define feature specific business logic.
|
||
- `DataCollector`, `Event`, `StageEvents`, etc.
|
||
|
||
## Testing
|
||
|
||
Since we have a lots of events and possible pairings, testing each pairing is not possible. The rule is to have at least one test case using an `Event` class.
|
||
|
||
Writing a test case for a stage using a new `Event` can be challenging since data must be created for both events. To make this a bit simpler, each test case must be implemented in the `data_collector_spec.rb` where the stage is tested through the `DataCollector`. Each test case will be turned into multiple tests, covering the following cases:
|
||
|
||
- Different parents: `Group` or `Project`
|
||
- Different calculations: `Median`, `RecordsFetcher` or `DataForDurationChart`
|