docs/execution-modes.md
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title: Execution modes
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Deepnote offers two modes of execution:
- **Block**: This runs only the selected block (or multiple blocks in the case of multi-selection).
- **Block and dependent blocks**. This runs the selected block and other blocks below it that depend on that block.
You can change the default execution mode for the notebook from the menu next to the **Run** button.
The current execution mode is displayed in the **Run** action in the block actions. You can override the default execution mode by selecting **Run this block** or **Run this block and dependent blocks below**.
## How are block dependencies detected?
In some cases, this process is straightforward; for example, a visualization block depending on a DataFrame, or a text input block defining Python variables used by other blocks.
However, with code blocks containing arbitrary user code, the problem becomes more complicated. These blocks can define new variables, reassign, or mutate them, potentially affecting other blocks.
### Directed Acyclic Graph (DAG)
Every code block, including code segments within SQL blocks using Jinja templates, is parsed into an Abstract Syntax Tree (AST). We traverse this AST to compile lists of variables used and defined by each block. By compiling these lists for every block in the notebook, along with their position in the notebook, we construct a Directed Acyclic Graph (DAG) of blocks.
When a block is executed, the DAG is traversed from the requested block downward. All blocks encountered during this traversal are executed.
You can view the DAG for a notebook anytime by clicking on the "Open dependency graph" button.