[jira] [Comment Edited] (APEXMALHAR-2026) Spooled Datastructures

["Timothy Farkas (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/APEXMALHAR-2026?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15225391#comment-15225391 ] 

Timothy Farkas edited comment on APEXMALHAR-2026 at 4/5/16 12:36 AM:
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Overall design proposal:

Spooled Data structures will be designed to work ontop of a key value store. Spooled data structures would be used as a component inside of an operator. The way the component would function is as followed:

StateFactory:

The StateFactory is an interface. The interface will have the setup, beginWindow, endWindow and teardown callbacks which an operator would have to call. The StateFactory is used to create handles to spooled DataStructures. The two types of spooled data structures it can create are Lists and Maps Like this.

StateFactory myFactory = new ManagedStateStateFactoryImpl();
List mySpooledList = myFactory.createNewList(byte[] keyPrefix, long bucket);
Map mySpooledMap = myFactory.createNewMap(byte[] keyPrefix, long bucket);
Map mySpooledMultiValuesMap = myFactory.createNewMultiValuedMap(byte[] keyPrefix, long bucket);

The StateFactory can have specific implementations for different backing stores, and can be set as a property on operators. More complex spooled datastructures can simple be created from spooled lists and maps.



was (Author: timothyfarkas):
Overall design proposal:

Spooled Data structures will be designed to work ontop of a key value store. Spooled data structures would be used as a component inside of an operator. The way the component would function is as followed:

- StateFactory:

The StateFactory is an interface. The interface will have the setup, beginWindow, endWindow and teardown callbacks which an operator would have to call. The StateFactory is used to create handles to spooled DataStructures. The two types of spooled data structures it can create are Lists and Maps Like this.

StateFactory myFactory = new ManagedStateStateFactoryImpl();
List mySpooledList = myFactory.createNewList(byte[] keyPrefix, long bucket);
Map mySpooledMap = myFactory.createNewMap(byte[] keyPrefix, long bucket);
Map mySpooledMultiValuesMap = myFactory.createNewMultiValuedMap(byte[] keyPrefix, long bucket);

The StateFactory can have specific implementations for different backing stores, and can be set as a property on operators. More complex spooled datastructures can simple be created from spooled lists and maps.


> Spooled 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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