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

["Beam JIRA Bot (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/BEAM-9008?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17177909#comment-17177909 ] 

Beam JIRA Bot commented on BEAM-9008:
-------------------------------------

This issue is assigned but has not received an update in 30 days so it has been labeled "stale-assigned". If you are still working on the issue, please give an update and remove the label. If you are no longer working on the issue, please unassign so someone else may work on it. In 7 days the issue will be automatically unassigned.

> 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
>              Labels: stale-assigned
>          Time Spent: 13h 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. 
>  
>  
>  



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