# Performance

Instant Replay keeps a short rolling buffer in your browser.

It’s designed to stay lightweight on normal pages.

On heavy pages, Screendesk can reduce or disable recording automatically.

<details>

<summary>How Instant Replay works (technical)</summary>

Instant Replay continuously records DOM changes (using rrweb-style snapshots and incremental updates).

Data is stored **locally** in memory and purged on a rolling window (about **2 minutes**).

When you trigger Instant Replay, Screendesk turns that buffer into a replay of what happened.

</details>

### What Screendesk does to stay fast

Screendesk reduces work in three main ways:

* **Samples and throttles events** instead of capturing everything.
* **Uses checkpoints** plus incremental updates instead of full snapshots all the time.
* **Keeps strict per-tab limits** and purges old data automatically.

<details>

<summary>Event sampling and throttling (defaults)</summary>

* Scroll events are throttled (about **150ms**, or **500ms** on heavier pages).
* Mouse moves are sampled rather than tracked continuously.
* Inputs capture the final value, not every keystroke.
* Non-essential events can be skipped (focus/blur/touch).

</details>

<details>

<summary>Snapshot strategy (defaults)</summary>

Full DOM snapshots are expensive.

Screendesk takes periodic checkpoint snapshots (about every **30 seconds**) and records incremental changes in between.

</details>

<details>

<summary>What we strip or disable</summary>

To reduce payload size, Screendesk removes or disables some data:

* Script tags and HTML comments
* Favicon and meta tag noise (social/robots/verification)
* Font collection
* Canvas and cross-origin iframe recording

</details>

<details>

<summary>Per-tab memory limits (defaults)</summary>

Typical caps per tab:

* DOM snapshots: **15MB**
* Console logs: **1MB**
* Network requests: **1MB**
* Total: **\~20MB**

</details>

### Heavy page detection

Some sites update constantly.

Those pages can spike CPU and memory.

Screendesk monitors activity and can disable Instant Replay recording on “heavy” pages.

Common examples:

* Realtime dashboards
* Trading and crypto tickers
* Spreadsheet apps (Google Sheets, Excel Online)
* Animation-heavy landing pages

{% hint style="info" %}
When Instant Replay is disabled on a heavy page, Screendesk can still capture console logs and network requests at a reduced rate.
{% endhint %}

### Override or block websites

Use Website management to control where Instant Replay runs.

See [Website management](/bug-reports/settings/website-management.md).

{% stepper %}
{% step %}

### Force-enable a heavy site

Open **Settings** → **Manage Websites**.

Add the domain to **Always Enabled Sites**.
{% endstep %}

{% step %}

### Block a site completely

Open **Settings** → **Manage Websites**.

Add the domain to **Blocked Sites**.
{% endstep %}
{% endstepper %}

### Priority order

Screendesk checks rules in this order:

1. **Blocked Sites** (always off)
2. **Always Enabled Sites** (always on)
3. **Automatic heavy page detection**
4. **Default behavior**


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