To create a hostname performance report in Piwik Pro Analytics, follow these steps:

1. Navigate to the Custom Report view in your Piwik Pro account.
2. Click on the Add a report button.
3. Choose flat table as your report type and select it.
4. Name your custom report and adjust the visibility if necessary.
5. Drag the Page URL dimension into the report.
6. Transform the Page URL into Hostnames by selecting Page URL (Domain) from the dropdown.
7. Add relevant metrics such as Visitors, Sessions, Goal Conversion, Goals Revenue, Goals Conversion Rate, Revenue, Orders, etc.

If no data appears during the report-building process, click Refresh Preview. Once satisfied, save the report to view and analyze the data.

The 'Collect data only from known sites' feature in Piwik Pro is a strict data collection setting that allows you to collect data only from sites whose web addresses you’ve added in the 'Site or app address' section. This feature helps protect your data against spam from unknown web addresses and is recommended to prevent unintentional data collection from staging domains, spammy domains, or domains not included in your data collection strategy.

It is important to check the hostnames in Piwik Pro Analytics for several reasons:

• To gain insight into the domains on which Piwik Pro Analytics is collecting data.
• To identify if any intended domain is not collecting data as it should.
• To understand the performance of your business domains based on aggregated metrics.
• To detect if you are collecting data from staging domains, spammy domains, or domains not intended to be included in your data collection strategy.
• To confirm that everything is in order regarding the hostnames where your business's Piwik Pro Analytics is collecting data.

To use the Piwik Pro alert feature for quality monitoring, you can set up alerts to proactively monitor data collection on new domains that you don’t own or want to include in your measurement strategy. This innovative use of Piwik Pro alerts allows you to stay informed about any unintended data collection without the need for additional tools. It's an effective way to maintain the quality and accuracy of your analytics data.