Xapian versions usually support several formats for index storage. A given major Xapian version will have a current format, used to create new indexes, and will also support the format from the previous major version.
Xapian will not convert automatically an existing index from the older format to the newer one. If you want to upgrade to the new format, or if a very old index needs to be converted because its format is not supported any more, you will have to explicitly delete the old index, then run a normal indexing process.
Using the -z option to
recollindex is not sufficient to change the
format, you will have to delete all files inside the index
directory (typically ~/.recoll/xapiandb)
before starting the indexing.
