I would never ever zip up a PostgreSQL data directory and expect it to restore elsewhere. I would use a proper export. If the export is too slow, it could help to use streaming replication to write intermediate files which can be moved to a backup location.

Even with SQLite, for a simple file copy to work reliably, one has to set these three:

  "_pragma=synchronous(FULL)",
  "_pragma=checkpoint_fullfsync(ON)",
  "_pragma=fullfsync(ON)",

Agreed about the Postgres export!

For sqlite, I would recommend "sqlite3 app.db '.backup backup.db'" though, if that's an option. Guaranteed consistent!