[jira] [Assigned] (BEAM-9008) Add readAll() method to CassandraIO

["Ismaël Mejía (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/BEAM-9008?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Ismaël Mejía reassigned BEAM-9008:
----------------------------------

    Assignee: vincent marquez

> Add readAll() method to CassandraIO
> -----------------------------------
>
>                 Key: BEAM-9008
>                 URL: https://issues.apache.org/jira/browse/BEAM-9008
>             Project: Beam
>          Issue Type: New Feature
>          Components: io-java-cassandra
>    Affects Versions: 2.16.0
>            Reporter: vincent marquez
>            Assignee: vincent marquez
>            Priority: P3
>          Time Spent: 15h 40m
>  Remaining Estimate: 0h
>
> When querying a large cassandra database, it's often *much* more useful to programatically generate the queries needed to to be run rather than reading all partitions and attempting some filtering.  
> As an example:
> {code:java}
> public class Event { 
>    @PartitionKey(0) public UUID accountId;
>    @PartitionKey(1)public String yearMonthDay; 
>    @ClusteringKey public UUID eventId;  
>    //other data...
> }{code}
> If there is ten years worth of data, you may want to only query one year's worth.  Here each token range would represent one 'token' but all events for the day. 
> {code:java}
> Set<UUID> accounts = getRelevantAccounts();
> Set<String> dateRange = generateDateRange("2018-01-01", "2019-01-01");
> PCollection<TokenRange> tokens = generateTokens(accounts, dateRange); 
> {code}
>  
>  I propose an additional _readAll()_ PTransform that can take a PCollection of token ranges and can return a PCollection<T> of what the query would return. 
> *Question: How much code should be in common between both methods?* 
> Currently the read connector already groups all partitions into a List of Token Ranges, so it would be simple to refactor the current read() based method to a 'ParDo' based one and have them both share the same function.  Reasons against sharing code between read and readAll
>  * Not having the read based method return a BoundedSource connector would mean losing the ability to know the size of the data returned
>  * Currently the CassandraReader executes all the grouped TokenRange queries *asynchronously* which is (maybe?) fine when all that's happening is splitting up all the partition ranges but terrible for executing potentially millions of queries. 
>  Reasons _for_ sharing code would be simplified code base and that both of the above issues would most likely have a negligable performance impact. 
>  
>  
>  



--
This message was sent by Atlassian Jira
(v8.3.4#803005)