If not revisions then we get a 404, so deal with that better.

ckanext/harvest/harvesters/ckanharvester.py

@@ -45,6 +45,9 @@ class CKANHarvester(HarvesterBase):
         try:
             http_response = urllib2.urlopen(http_request)
         except urllib2.HTTPError, e:
+            if e.getcode() == 404:
+                raise ContentNotFoundError('HTTP error: %s' % e.code)
+            else:
                 raise ContentFetchError('HTTP error: %s' % e.code)
         except urllib2.URLError, e:
             raise ContentFetchError('URL error: %s' % e.reason)
@@ -205,11 +208,15 @@ class CKANHarvester(HarvesterBase):
                             revision = json.loads(content)
                             package_ids = revision['packages']
                     else:
-                        log.info('No packages have been updated on the remote CKAN instance since the last harvest job')
+                        log.info('No revisions since last harvest %s',
+                                 last_time)
                         return []
 
+                except ContentNotFoundError, e:
+                    log.info('No revisions since last harvest %s', last_time)
+                    return []
                 except ContentFetchError, e:
-                    # Any error at all indicates that revision filtering is not
+                    # Any other error indicates that revision filtering is not
                     # working for whatever reason, so fallback to just getting
                     # all the packages, which is expensive but reliable.
                     log.info('CKAN instance %s does not suport revision '
@@ -468,5 +475,8 @@ class CKANHarvester(HarvesterBase):
 class ContentFetchError(Exception):
     pass
 
+class ContentNotFoundError(ContentFetchError):
+    pass
+
 class RemoteResourceError(Exception):
     pass