[jira] [Commented] (APEXMALHAR-2026) Spill-able Datastructures

["ASF GitHub Bot (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/APEXMALHAR-2026?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15337491#comment-15337491 ] 

ASF GitHub Bot commented on APEXMALHAR-2026:
--------------------------------------------

Github user tweise commented on a diff in the pull request:

    https://github.com/apache/apex-malhar/pull/319#discussion_r67594736
  
    --- Diff: stream/src/main/java/org/apache/apex/malhar/stream/window/impl/DefaultWindowedStorageImpl.java ---
    @@ -0,0 +1,120 @@
    +package org.apache.apex.malhar.stream.window.impl;
    +
    +import com.datatorrent.api.StreamCodec;
    +import org.apache.apex.malhar.stream.window.Window;
    +import org.apache.apex.malhar.stream.window.WindowedStorage;
    +
    +import java.util.Collections;
    +import java.util.HashMap;
    +import java.util.Map;
    +import java.util.Set;
    +import java.util.TreeMap;
    +import java.util.TreeSet;
    +
    +/**
    + * Created by david on 6/14/16.
    + */
    +public class DefaultWindowedStorageImpl<K, V> implements WindowedStorage<K, V>
    --- End diff --
    
    In the spirit of designing an interface that allows for efficient storage operation with large state, can you consider 
    https://issues.apache.org/jira/browse/APEXMALHAR-2026
    as well as managed state?


> Spill-able Datastructures
> -------------------------
>
>                 Key: APEXMALHAR-2026
>                 URL: https://issues.apache.org/jira/browse/APEXMALHAR-2026
>             Project: Apache Apex Malhar
>          Issue Type: New Feature
>            Reporter: Timothy Farkas
>            Assignee: Timothy Farkas
>              Labels: roadmap
>
> Add libraryies for spooling datastructures to a key value store. There are several customer use cases which require spooled data structures.
> 1 - Some operators like AbstractFileInputOperator have ever growing state. This is an issue because eventually the state of the operator will grow larger than the memory allocated to the operator, which will cause the operator to perpetually fail. However if the operator's datastructures are spooled then the operator will never run out of memory.
> 2 - Some users have requested for the ability to maintain a map as well as a list of keys over which to iterate. Most key value stores don't provide this functionality. However, with spooled datastructures this functionality can be provided by maintaining a spooled map and an iterable set of keys.
> 3 - Some users have requested building graph databases within APEX. This would require implementing a spooled graph data structure.
> 4 - Another use case for spooled data structures is database operators. Database operators need to write data to a data base, but sometimes the database is down. In this case most of the database operators repeatedly fail until the database comes back up. In order to avoid constant failures the database operator need to writes data to a queue when the data base is down, then when the database is up the operator need to take data from the queue and write it to the database. In the case of a database failure this queue will grow larger than the total amount of memory available to the operator, so the queue should be spooled in order to prevent the operator from failing.
> 5 - Any operator which needs to maintain a large data structure in memory currently needs to have that data serialized and written out to HDFS with every checkpoint. This is costly when the data structure is large. If the data structure is spooled, then only the changes to the data structure are written out to HDFS instead of the entire data structure.
> 6 - Also building an Apex Native database for aggregations requires indices. These indices need to take the form of spooled data structures.
> 7 - In the future any operator which needs to maintain a data structure larger than the memory available to it will need to spool the data structure.



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