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The merge operation is designed to combine two or more indexes into one index to accelerate the search and to simplify the work with indexes. When merging, only the index at which the merge method was called is changed. This index as a result of the operation contains all the documents that were contained in all indexes together. The second index or index repository after the merge can be deleted to free up disk space.

The MergeOptions class contains a method for specifying a cancellation object, as well as a method for specifying whether the operation will be performed asynchronously. By default, index merging operation is performed synchronously.

The Index class has method overloads for merging a single index and a whole index repository. Before performing a merge, checks are made to ensure that the indexes are of the same type. Merging is performed only on those indexes that have the same IndexType value as the index on which the merge method is called.

The following example demonstrates the merging of two indexes.

String indexFolder1 = "c:\\MyIndex1\\";
String indexFolder2 = "c:\\MyIndex2\\";
String documentsFolder1 = "c:\\MyDocuments1\\";
String documentsFolder2 = "c:\\MyDocuments2\\";
 
Index index1 = new Index(indexFolder1); // Creating index1
index1.add(documentsFolder1); // Indexing documents
 
Index index2 = new Index(indexFolder2); // Creating index2
index2.add(documentsFolder2); // Indexing documents
 
MergeOptions options = new MergeOptions();
options.setCancellation(new Cancellation()); // Creating cancellation object to be able to cancel the oparation
 
// Merging index2 into index1
// Files of index2 will not be changed
index1.merge(index2, options);

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