A method includes extracting variable length strings from text data, associating the extracted strings with indexes in an indexing structure that maintain identifiers for instances of the strings in the text data, selecting a set of the strings having corresponding indexes whose size exceeds a threshold size value, and determining whether to merge a first index corresponding to a first string with a second index corresponding to a second string, the second string being a sub string of the first string, wherein the determination is based at least in part on a comparison of a first size of the first index and a second size of the second index. The method further includes merging the first index with the second index to create a merged index in the indexing structure responsive to the determination, and processing queries to the text data utilizing the indexing structure with the merged index.