Select/delete all items in Solr
To select all items for a field in Solr you can use the query : some_item:[* TO *], but if this field is missing from some documents you will not select those documents.
To select all documents you can use the id defined in /conf/schema.xml, for example: <uniqueKey>solr_id</uniqueKey> you can use solr_id:[* TO *].
Now that you have all documents selected you can delete them 
To delete all documents in Solr use this update xml:
<delete><query>solr_id:[*TO *]</query></delete>
and of course you have to commit:
<commit />
That’s all !
Source: http://blog.tremend.ro/2007/03/02/selectdelete-all-items-in-solr/
You can find all docs (with or without a uniqueKey field) using *:*
Likewise you can delete all docs using that query as well … but if your index is particularly huge it can be more efficient in Solr 1.2 to just stop solr, rm -r the index directory and start solr again.
in Solr 1.3, *:* will be be as efficient as rm’ing the directory yourself, but without needing to start/stop.
Hoss
July 14, 2008 at 1:29 am