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https://issues.apache.org/jira/browse/MAHOUT-247?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Sean Owen resolved MAHOUT-247.
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Resolution: Fixed
Tentatively resolving this after applying a fix to the most obvious case where
this issue could come up. It's not truly fixed in all cases, though at the
moment, I think this is all that is practical to attempt. I'm open to more
suggestions about how to address this.
> GenericUserBasedRecommender.recommend causes connection leak when called for
> user with no preferences
> -----------------------------------------------------------------------------------------------------
>
> Key: MAHOUT-247
> URL: https://issues.apache.org/jira/browse/MAHOUT-247
> Project: Mahout
> Issue Type: Bug
> Components: Collaborative Filtering
> Affects Versions: 0.2
> Environment: Reproducable on Win32 and Ubuntu
> Reporter: Tolga Oral
> Assignee: Sean Owen
> Priority: Minor
> Fix For: 0.3
>
>
> UserSimilarity userSimilarity = new
> TanimotoCoefficientSimilarity(getBooleanPrefDataModel());
> UserNeighborhood neighborhood = new
> NearestNUserNeighborhood(3, userSimilarity, getBooleanPrefDataModel());
> Recommender recommender = new
> GenericBooleanPrefUserBasedRecommender(getBooleanPrefDataModel(),
> neighborhood, userSimilarity);
> recommender.recommend(userwithnopreferencesdata, 10);
> code properly throws NoSuchUserException however one of the connections is
> hang on LongPrimitiveIterator backed by
> org.apache.mahout.cf.taste.impl.model.jdbc.AbstractJDBCDataModel$ResultSetIDIterator
> as Exception is thrown before TopItems.getTopUsers finishes the while loop
> public static long[] getTopUsers(int howMany,
> LongPrimitiveIterator allUserIDs,
> Rescorer<Long> rescorer,
> Estimator<Long> estimator) throws
> TasteException {
> Queue<SimilarUser> topUsers = new PriorityQueue<SimilarUser>(howMany + 1,
> Collections.reverseOrder());
> boolean full = false;
> double lowestTopValue = Double.NEGATIVE_INFINITY;
> //HERE IS THE ITERATOR
> while (allUserIDs.hasNext()) {
> long userID = allUserIDs.next();
> if (rescorer != null && rescorer.isFiltered(userID)) {
> continue;
> }
> //EXCEPTION THROWN HERE CAUSES THE CONNECTION LEAK
> double similarity = estimator.estimate(userID);
> double rescoredSimilarity = rescorer == null ? similarity :
> rescorer.rescore(userID, similarity);
> if (!Double.isNaN(rescoredSimilarity) && (!full || rescoredSimilarity >
> lowestTopValue)) {
> topUsers.add(new SimilarUser(userID, similarity));
> if (full) {
> topUsers.poll();
> } else if (topUsers.size() > howMany) {
> full = true;
> topUsers.poll();
> }
> lowestTopValue = topUsers.peek().getSimilarity();
> }
> }
> if (topUsers.isEmpty()) {
> return NO_IDS;
> }
> List<SimilarUser> sorted = new ArrayList<SimilarUser>(topUsers.size());
> sorted.addAll(topUsers);
> Collections.sort(sorted);
> long[] result = new long[sorted.size()];
> int i = 0;
> for (SimilarUser similarUser : sorted) {
> result[i++] = similarUser.getUserID();
> }
> return result;
> }
> ============================================================================================================
> I currently fixed it in our application by checking first to see if user has
> preferences for the given dataset (user might exists and have preferences for
> a different dataset).
> However this edge case does not cause issues in some other recommenders as
> long as we handle the NoSuchUserException.
> Easy solution is to use AbstractJDBCDataModel$ResultSetIDIterator always with
> try/catch/finally and release the connection.
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