# Branches Source: https://stratadb.org/docs/learn/branches A branch is a named line of database state. Every key, document, event, vector and graph row belongs to one. A new database starts with a single branch called `default`, and unless you say otherwise that is the branch you are reading and writing. Branches are not a collaboration feature and there is no remote to push them to. They are workspaces: an isolated place to make changes, whether that is a data cleanup you might abandon, an index you are rebuilding, or a task you handed to an agent and want to inspect before any of it counts. ## Versions, and the point you branched from A version is a committed point in the database's history. Every write produces one, and a branch advances through them. When you create a branch from another, Strata records the version you left from. That is the branch point, and it is what makes every later question answerable: what changed on my side, what changed on theirs, and what a merge would have to reconcile. You never supply it. Strata derives it from the lineage it recorded at fork time, which is why comparing two unrelated branches fails rather than guessing. > **Figure.** A branch leaves its parent at a specific version, the branch point. Both lines then advance independently, and a merge lands as a new version on the target rather than rewriting the versions behind it. You can see the lineage on the branch itself: ```console strata branch get cleaned ``` The `parent` block names the branch it came from and the `fork_version` it left at. ## Forking does not copy the data `strata branch fork default cleaned` gives you every key, document and vector the source branch could see, and copies none of it. The new branch shares its parent's storage and diverges only where you write. That is worth being concrete about. Forking a 20 KB database costs about 1.5 KB. Forking a 730 KB database, thirty-six times the data, costs about the same 1.5 KB. What a fork writes is the record of the branch, not a copy of what it can see. The consequence is that branches stop being something you ration. You can give every experiment one, keep ten of them side by side, and delete the ones that did not work out without having paid for them. ## Comparing two branches ```console strata branch diff default cleaned ``` The comparison is organised by space and by data model, and reports what was added, removed and modified on each side since the branch point. It takes an `--as-of` timestamp if you want to compare the two branches as they stood earlier rather than now. ## Previewing before you merge A merge changes the target branch, so Strata will tell you what it would do first: ```console strata branch preview cleaned default ``` Preview answers three things. Whether the merge can apply at all. Which conflicts it would hit, with the source value and the target value for each. And which data models it covered. It does not touch the target branch, so you can ask as often as you like. ## Merging ```console strata branch merge cleaned default ``` The source branch is applied to the target. The target gains a new version; the source is left exactly as it was, so merging does not consume the branch you merged from. The operation is all or nothing. Two strategies decide what happens when both sides changed the same thing: - **`strict`**, the default, refuses the whole merge if there is any conflict. You get the error `conflict.engine.promotion` and the target is untouched. - **`source-wins`** applies the source side's value for each conflict. The safe one is the default deliberately. A merge that silently picks a winner is a merge you find out about later. ## What a merge covers This is the part to know before you rely on it. A merge covers key-value data, JSON documents and vectors. It does not cover events, graph data or vector collections. You do not have to remember that list. Preview and merge both report it, as `capabilities_covered` and `capabilities_unsupported`, against the actual release you are running. Read it before merging a branch whose interesting changes were graph edges. ## The vocabulary, briefly Strata's own receipts and error codes say **promotion** where this page says merge, because the engine describes the operation as promoting one branch's changes into another. The command is `merge`, and that is the word these docs use. If you see `conflict.engine.promotion` in an error, it is talking about the merge you just attempted.