Mystery of memory fraction in Showplan XML

If you examine Showplan XML, you may find an entry like  <MemoryFractions Input=”1″ Output=”1″ /> on some operators .  They are internal parameters used by query memory grant to save overall memory usage, and “fraction” means how much this operator is allowed to use from “total additional memory” (please see previous post for definition on additional memory)….


How to Check Whether the Final Query Plan is Optimized for Star Join Queries?

The star join optimization technique is an index based optimization designed for data warehousing scenarios to make optimal use of non-clustered indexes on the huge fact tables. The general idea is to use the non-clustered indexes on the fact table to limit the number of rows scanned from it. More details of index based star…


Showplan Trace Events

Besides SSMS, another great tool available to database developers and DBAs to view query plans and troubleshoot query compilation or execution issues is the SQL Server Profiler. In the Profiler, all the showplan events are listed under the Performance Event category. All the SQL Trace events generate showplan information at query-level granularity, i.e. a single…


Viewing and Interpreting XML Showplans

As mentioned in our previous blog posting, SQL Server 2005 supports Showplan generation in XML format. XML-based Showplans provide greater flexibility in viewing query plans and saving them to files as compared to legacy Showplans. In addition to the usability benefits, XML-based Showplans also contain certain plan-specific information which is not available in Legacy Showplans. For example, Showplan XML contains the cached plan…


Introduction to Showplan

Showplan is a feature in SQL Server to display and read query plans. While some of you may already be very familiar with Showplan, it is one of the most important diagnostic tools that we use in the query processing team to locate and identify problems, and therefore deserves some extra exposure.  Being able to…