Full Text Search Index Creation: Temporary File Size

Advantage Concepts

While creating FTS indexes, Advantage may create very large temporary files. The temporary sort file will have one key for every word in the information being indexed. This includes duplicate words as well. The space that is required for each key in the temporary file is the maximum word length plus 4 bytes of overhead per key. As the actual index is built, duplicates are removed and key compression is used, so the final index size can be quite small. Consider an example:

(1048576 / 6)* 64 = 11,184,810 (about 11 MB).

In the above example, the temporary file size has a 10:1 ratio in size with the data. The final index size is completely dependent on the data. In one test case, the total data was 84 MB, the temporary sort file was 400 MB, and the final index size was 2 MB. Another test case included 2.3 MB of data, 8 MB of temporary space, and a final index size of 0.25 MB.