A branch is the unit of logical separation for Fennel datasets & featuresets within a cluster. A cluster can have many branches and each branch can have many independent datasets & featuresets. Fennel's branch semantics are heavily inspired by Git.

2client.checkout("branch1")  # noop: init_branch checks out new branch
4    message="some module: some git like commit message",
5    datasets=[Dataset],
6    featuresets=[SomeFeatureSet],
10client.checkout("branch2")  # noop: init_branch checks out new branch
12    message="another module: some git like commit message",
13    datasets=[Dataset],
14    featuresets=[OtherFeatureSet],
Managing multiple branches


In the above example, we have two branches - branch1 and branch2. They both have the same dataset but different featuresets. In general, their entity graphs are completely independent of each other and can be queried for features independently as well. Queries are always made against a particular branch (which by default is the main branch).

At any point of time, a given client instance is pointing to a particular branch. checkout merely changes the branch pointed to by the client. It's okay to have multiple client objects with different branches checked out.

Main Branch

By default, Fennel creates a default branch called "main". All branch operations talk to this branch if not explicitly specified. The only thing special about this branch is that it can not be deleted - outside of that, it's just a regular branch. All branches are equally suitable to be used in any production or experimental setting.

Branch Cloning

In addition to creating new empty branches via init_branch method on the client, Fennel also supports cloning an existing branch. The new cloned branch gets an independent copy of all the datasets/featuresets in the original branch. After the clone, the datasets/featuresets in the new branch can be modified arbitrarily without influencing the original branch.

4    message="branch1: initial commit",
5    datasets=[SomeDataset],
6    featuresets=[SomeFeatureset],
9client.clone_branch(name="branch2", from_branch="branch1")
Cloning branch1 into a new branch branch2


Copy-on-Write Clone

Fennel datasets/featuresets are logically isolated across branches and can be modified independently. However, behind the scenes, Fennel uses copy-on-write like semantics and maintains the same physical representation (for both storage & compute) for identical entities across branches.

As a result, cloning an existing branch is extremely cheap. This makes cloning ideal for those workflows when you want to modify just a couple of datasets/featuresets and keep the rest of the graph unchanged.

Note that the copy on write semantics don't depend on the branch being cloned. For instance, if you created an empty branch via init_branch and committed the same dataset/featureset definitions to it explicitly, Fennel is smart enough to still use the same physical assets to power the two branches.

Branch Management


Fennel Console

You can also use Fennel console to browse through all the existing branches. For any given branch, you can see all its datasets/featuresets, inspect live dataflow etc. as well as see the full commit log.

Access Control

Cloning a branch requires read/write access to all tags used in the entities of the original branch. Additionally, it's possible to setup RBAC system such that branch creation, cloning, and deletion require elevated permissions.

Branch Deletion

Branches can also be deleted via delete_branch method on the client. It's advisable to periodically prune unused/inactive branches so as to potentially free up underlying storage/compute resources. Note that due to copy-on-write, all branches pointing to a dataset/featureset need to be deleted to clean up the underlying resources.

Branch Workflows

Branches are flexible enough to be adapted to many workflows. Here are some of the most common examples.

Dev Branch per Developer

It's easy to create one (or more) branch per developer - that way, developers can do development against their branch without getting in the way of each other. When ready, the changes can be committed to some common standard branches.

Dev Branch per Git Branch

Many teams develop in project specific git branches. It's possible to create one Fennel branch per git branch for do all Fennel related changes in that project.

Dev Branch for Integration Tests

Fennel's mock client provides native support for Python unit tests. However, if you want to set integration tests involving real server as well, you could write some test fixtures that spin up a branch with a random name in the test/dev cluster, execute the test in that branch and tear down the branch after the test is finished.

Branch per A/B Test

All Fennel branches are equally production ready and can serve live production traffic. As a result, it's possible to create Fennel branches for each variant of an A/B test and have different users query different branches.

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