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Troubleshooting: Slow Full-Text Indexing Performance Due to Filtering Process

When populating a full-text index, the Full-Text Engine uses two types of filters: multithreaded and single-threaded. Some documents, such as Microsoft Word documents, are filtered using a multithreaded filter. Other documents, such as Adobe Acrobat Portable Document Format (PDF) documents, are filtered using a single-threaded filter.

For security reasons, in SQL Server 2008, filters are loaded by filter daemon host processes. A server instance uses a multithreaded process for all multithreaded filters and a single-threaded process for all single-threaded filters. When a document that uses a multithreaded filter contains an embedded document that uses a single-threaded filter, the Full-Text Engine launches a single-threaded process for the embedded document. For example, on encountering a Word document that contains a PDF document, the Full-Text Engine uses the multithreaded process for the Word content and launches a single-threaded process for the PDF content. A single-threaded filter might not work well in this environment, however, and could destabilize the filtering process. In certain circumstances where such embedding is common, destabilization might lead to filtering-process crashes. When this occurs, the Full-Text Engine re-routes any failed document (for example, a Word document that contains embedded PDF content) to the single-threaded filtering process. If re-routing occurs frequently, it results in performance degradation of the full-text indexing process.

To work around this problem, mark the filter for the container document (Word in this case) as a single-threaded filter. You can change the filter registry value to mark a given filter as a single-threaded filter. To mark a filter as a single-threaded filter, you need to set the ThreadingModel registry value for the filter to Apartment Threaded. For information about single-threaded apartments, see Understanding and Using COM Threading Models.

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