dtSearch index formats and compatibility between versions.
Generally, newer versions of dtSearch can search and update indexes created by older versions, going back to version 6.
File parser changes between versions may cause hit highlighting to appear incorrectly in retrieved documents when a different dtSearch version is used to search an index than was used to create the index. This is because dtSearch stores word offsets in the index, and when a file parser changes in a way that affects word counting, the same word offset may point to a different word when a newer file parser is used.
In practice, this usually affects a very small percentage of documents with each minor update. When upgrading across many versions (for example, from version 7.22 to 7.64), a significant percentage of documents may be affected.
To correct this, rebuild the index with the current dtSearch version. You can also use the flag dtsConvertAutoUpdateSearch with FileConverter to have it automatically update the locations of hits to take into account any file parser changes or changes in the file since it was indexed.
dtSearch 7 can read and update indexes created with any of the dtSearch 6.x versions.
The format of an index is automatically detected when the index is opened, so there is no need to specify when updating or searching an index what the format of the index is.
Upgrading an index
Compressing a version 6 index using version 7 of the dtSearch Engine will automatically convert the index to the version 7 format.