# 18. Free Text Search

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Preface
Free Text Search
Basic Concepts
Creating Free Text Indexes
Querying Free Text Indexes
Text Triggers
Generated Tables and Internals
Removing A Text Index
Removing A Text Trigger
Internationalization & Unicode
Performance
Restrictions
Free Text Functions

## 18.9. Performance

For indexing large volumes it is critical to run the indexing process over large volumes of data. This is accomplished by using the batch update mode. This is activated with the VT_BATCH_UPDATE procedure.

When this mode is on the index will be updated after a settable interval, doing all the updates accumulated since the last batch in a single go. The size of a single batch is configurable in the virtuoso.ini file using the FreeTextBatchSize option. This is the number of bytes of text which will be processed as one sweep over the index. A value of 1MB is often suitable. Even All changes are processed in a batch at the set interval. If there are more characters of text to index / unindex than the batch size, the operation is broken into several transactions, each processing about FreeTextBatchSize bytes worth of text. This improves concurrency and cuts down on locking.

The command

    DB.DBA.vt_batch_update ('DB.DBA.ARTICLE', 'ON', 1);

turns on the batch mode for the article table with a 1 minute delay between index refreshes. The table name must be fully qualified and is case sensitive. The correct case is seen in the administration interface tables list of the isql tables command etc.

### 18.9.1. Restrictions

If the free text document ID is an integer, which is encouraged for compactness, the values 0 and negative are reserved.

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