> For the complete documentation index, see [llms.txt](https://docs.apryse.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.apryse.com/web/get-started/faq/what-is-the-bcid.md).

# What is the BCID?

World's #1 PDF SDK Library for Web, Mobile, Server, Desktop

### What is the BCID?

When Webviewer attempts to connect to a WebViewer Server instance it will include a query parameter called `BCID` when using versions of WebViewer above 7.0. This parameter is used in conjunction with our `wv-loadbalancer` to maintain client stickiness to individual servers during document sessions.

Every time a document is opened in WebViewer, a new `BCID` is generated. The `wv-loadbalancer` will then see this ID and assign it to one of its available servers. During that documents life, the connection will be tied to a specific server. Once another document is opened, this `BCID` is generated again, and the `wv-loadbalancer` chooses a server for this new session.

You can leverage this `BCID` to maintain stickiness for your instance of WebViewer Server even if you are not using our load balancer. The following code is how this is done inside of HAProxy.

{% tabs %}
{% tab title="Bash" %}
{% code lineNumbers="true" %}

```bash
# create a stick table and stick on the query parameter 'bcid'
stick-table type string len 40 size 5M expire 1d
stick on url_param(bcid)
```

{% endcode %}
{% endtab %}
{% endtabs %}

This `BCID` can be used in conjunction with what was discussed in this [guide](/web/get-started/faq/load_balancing.md)

You can access the [BCID client side in WebViewer](/web/webviewer-server/wv-server-hardware-and-network.md#retrieving-the-bcid) by following the directions.


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