FTS does not work in projects migrated from 6.5 or earlier

[IskandarovRost]

See: https://www.cuba-platform.com/discuss/t/demo-not-woking-fts/6163

Environment

• Platform version: 6.9.5

Description of the bug or enhancement

• Minimal reproducible example

1. Create a project on the platform version 6.5
2. Enable FTS
3. ReindexAll and ProcessQueue
4. Migrate the project to 6.9, update Db
5. Launch Reindex all or try to search something

• Actual behavior The index could not be deleted and FTS also doews not work

org.apache.lucene.index.IndexFormatTooOldException: Format version is not supported (resource BufferedChecksumIndexInput(MMapIndexInput(path="D:\studioSN\2018.08.16\fts65\deploy\tomcat\work\app-core\ftsindex\segments_3"))): this index is too old (version: 5.3.0). This version of Lucene only supports indexes created with release 6.0 and later.

Alternative script:

1. Open https://demo.cuba-platform.com/app/#!
2. Try to search something

[alexbudarov]

The worst problem here is that you can't repair FTS indices without stopping the server.
You have to:

• stop the server
• delete indices from the disk (rm -rf $tomcatDir/work/app-core/ftsindex)
• start the server and reindex from scratch.

This is very inconvenient.