# Basic operations

(memory-basic-operations-taking-a-heap-snapshot)=

## Taking a heap snapshot

To take a snapshot of the heap, click the "Take snapshot" button, or the camera icon on the left:

```{image} memory-1-small.png
:class: center
```

The snapshot will occupy the large pane on the right-hand side. On the left, you'll see an entry for the new snapshot, including its timestamp, size, and controls to save or clear this snapshot:

```{image} memory-2-small.png
:class: center
```

(memory-basic-operations-clearing-a-snapshot)=

## Clearing a snapshot

To remove a snapshot, click the "X" icon:

```{image} memory-3-small.png
:class: center
```

(memory-basic-operations-saving-and-loading-snapshots)=

## Saving and loading snapshots

If you close the Memory tool, all unsaved snapshots will be discarded. To save a snapshot click "Save":

```{image} memory-4-small.png
:class: center
```

You'll be prompted for a name and location, and the file will be saved with an `.fxsnapshot` extension.

To load a snapshot from an existing `.fxsnapshot` file, click the import button, which looks like a rectangle with an arrow rising from it:

```{image} memory-5-small.png
:class: center
```

You'll be prompted to find a snapshot file on disk.

(memory-basic-operations-comparing-snapshots)=

## Comparing snapshots

You can diff two heap snapshots. The diff shows you where memory was allocated or freed between the two snapshots.

To create a diff, click the button that looks like a Venn diagram next to the camera icon:

```{image} memory-6-small.png
:class: center
```

You'll be prompted to select the snapshot to use as a baseline, then the snapshot to compare. The tool then shows you the differences between the two snapshots:

```{raw} html
<iframe width="560" height="315" src="https://www.youtube.com/embed/3Ow-mdK6b2M" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>
<br/>
<br/>
```

:::{note}
When you're looking at a comparison, you can't use the Dominators view or the Tree Map view.
:::

(memory-basic-operations-recording-call-stacks)=

## Recording call stacks

The Memory tool can tell you exactly where in your code you are allocating memory. However, recording this information has a run-time cost, so you must ask the tool to record memory calls *before* the memory is allocated, if you want to see memory call sites in the snapshot. To do this, check "Record call stacks":

```{image} memory-7-small.png
:class: center
```
