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

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

     [ https://issues.apache.org/jira/browse/BEAM-9008?focusedWorklogId=375209&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-375209 ]

ASF GitHub Bot logged work on BEAM-9008:
----------------------------------------

                Author: ASF GitHub Bot
            Created on: 21/Jan/20 20:58
            Start Date: 21/Jan/20 20:58
    Worklog Time Spent: 10m 
      Work Description: vmarquez commented on pull request #10546: [BEAM-9008] Add CassandraIO readAll method
URL: https://github.com/apache/beam/pull/10546#discussion_r369239579
 
 

 ##########
 File path: sdks/java/io/cassandra/src/main/java/org/apache/beam/sdk/io/cassandra/QueryFn.java
 ##########
 @@ -0,0 +1,89 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.beam.sdk.io.cassandra;
+
+import com.datastax.driver.core.Cluster;
+import com.datastax.driver.core.ColumnMetadata;
+import com.datastax.driver.core.PreparedStatement;
+import com.datastax.driver.core.ResultSet;
+import com.datastax.driver.core.Session;
+import com.datastax.driver.core.Token;
+import java.util.Iterator;
+import java.util.stream.Collectors;
+import org.apache.beam.sdk.transforms.DoFn;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class QueryFn<T> extends DoFn<Iterable<RingRange>, T> {
 
 Review comment:
   I don't think we want this flattened here, the way I'm using readAll currently is I am hashing into groups of queries based on actual shard, which is owned by a core (in ScyllaDB), so grouping queries gives finer grained control over how much load we put on a core.  Someone using cassandra could use a similar split idea for making sure to limit the number of concurrent TokenRanges owned by the same node in Cassandra. 
 
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Issue Time Tracking
-------------------

    Worklog Id:     (was: 375209)
    Time Spent: 2h 20m  (was: 2h 10m)

> 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: Minor
>          Time Spent: 2h 20m
>  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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