If there were no changes since this instance was opened or last refreshed, then this call does nothing. Note, however, that this is still a relatively slow method (as it needs to verify whether there have been any changes on disk to the taxonomy), so it should not be called too often needlessly. In faceted search, the taxonomy reader's refresh() should be called only after a reopen() of the main index.
It should be noted that refresh() is similar in purpose to IndexReader.reopen(), but the two methods behave differently. refresh() refreshes the existing TaxonomyReader object, rather than opening a new one in addition to the old one as reopen() does. The reason is that in a taxonomy, one can only add new categories and cannot modify or delete existing categories; Therefore, there is no reason to keep an old snapshot of the taxonomy open - refreshing the taxonomy to the newest data and using this new snapshots in all threads (whether new or old) is fine. This saves us needing to keep multiple copies of the taxonomy open in memory.
| |
| |