Microsoft Sharepoint Products and Technologies Resource Kit eBook

600 Part VII: Information Management in SharePoint Products and Technologies
Incremental (Inclusive) Update
SharePoint Portal Server 2003 changed the incremental update to make it more efficient
and less resource intensive. To allow for changes that the incremental update
does not check for, SharePoint Portal Server 2003 included a new type of update
called the incremental (inclusive) update. This update is similar to the incremental
update except that the incremental (inclusive) update removes deleted content from
the index. Otherwise, this update is similar to the incremental update in SharePoint
Portal Server 2001. The incremental (inclusive) update is more resource intensive
than the regular incremental update and should therefore be run less often. The
incremental update is the least resource-intensive update.
Adaptive Update
An adaptive update builds a statistical model for the content source and crawls only
the content that, statistically speaking, is more likely to have changed since the last
update. Unlike the incremental update, the adaptive update increases its efficiency
by “learning” which content changes and at what frequency, and then it molds its
crawling schedule accordingly.
How Adaptive Updates Work
To decide which documents to crawl, adaptive updates gather change information
each time an update is performed on a content source. This information is used to
determine which documents are most likely to change. Because of this, the efficiency
of adaptive updates increases over time and over multiple updates. As more
updates are performed, more statistical samples are available to the algorithm. After
a week of daily adaptive updates, the system settles into a steady state. A steady
state is a state in which the system has acquired enough information for the adaptive
update to function at optimal efficiency.
Improving Performance with Adaptive Updates
The algorithm used by adaptive updates computes statistical information regardless
of the type of update SharePoint Portal Server performs. If incremental updates are
run first and then later adaptive updates are used, performance improves immediately
because the system is already in a steady state. This is because SharePoint
Portal Server has already accumulated sufficient statistical information to apply the
algorithm.
Performance improvement between an adaptive update and an incremental
update depends on the number of documents and the frequency of changes to the
documents. The higher the percentage of documents that change infrequently, the
better the performance is. Adaptive updates show the most significant performance
improvement in collections of more than 2500 documents.