This should be one of the first things a BizTalk administrator optimizes on a production BizTalk environment. It’s a quick easy win intended to optimize BizTalk Server for low latency by reducing the amount of overhead incurred when shipping data between the message box and tracking/BAM databases.
As a bit of background each BizTalk Server host instance is responsible for a number of tasks including the execution of business process, shipping tracking data from to the BizTalkDTADb database, and shipping BAM data to the BAMPrimaryImport database. Data is flagged within the message box to be shipped to the tracking database and BAM database. The component within a BizTalk host shipping this data is known as TDDS(tracking data decode service) or otherwise the BAM Event Bus Service.
A host with tracking enabled is essentially enabling TDDS to run under that host making that host responsible for both processing business process and performing the background tasks of shipping tracking data. It’s worth noting TDDS doesn’t care that tracking data originated from a business process running under another host. TDDS acts as a mule simply pulling the data from the message box. This means we can dedicate any host to shipping all tracking data from the message box.
It is important to note here having no hosts running with tracking enabled WILL result in message box growth and eventually slow down BizTalk performance. To view the size of the tracking data ready to be shipped in the message box watch the "Tracking Data Size" general BizTalk performance counter. It’s optimal to have at least one BizTalk tracking host for each message box database. The number of host instances running TDDS should be (N+1) with N being the number of message boxes and 1 being for redundancy. E.g. A BizTalk environment with one message box should have tracking enabled on one host, host instances should run on (1+1) = 2 BizTalk Server computers.
I typically dedicate the BizTalkServerApplication host to tracking only. Each BizTalk application runs under seperate host/s with tracking disabled therefore being dedicated purely to processing messages/orchestrations and as a result improving performance by removing the need for those hosts to perform any back ground shipment of tracking and BAM data.