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https://issues.apache.org/jira/browse/BEAM-9008?focusedWorklogId=501161&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-501161
]
ASF GitHub Bot logged work on BEAM-9008:
----------------------------------------
Author: ASF GitHub Bot
Created on: 15/Oct/20 16:44
Start Date: 15/Oct/20 16:44
Worklog Time Spent: 10m
Work Description: vmarquez commented on a change in pull request #10546:
URL: https://github.com/apache/beam/pull/10546#discussion_r505688957
##########
File path:
sdks/java/io/cassandra/src/main/java/org/apache/beam/sdk/io/cassandra/ReadFn.java
##########
@@ -0,0 +1,172 @@
+/*
+ * 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.Collections;
+import java.util.Iterator;
+import java.util.Set;
+import java.util.stream.Collectors;
+import org.apache.beam.sdk.io.cassandra.CassandraIO.Read;
+import org.apache.beam.sdk.transforms.DoFn;
+import org.apache.beam.vendor.guava.v26_0_jre.com.google.common.base.Joiner;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+class ReadFn<T> extends DoFn<Read<T>, T> {
+
+ private static final Logger LOG = LoggerFactory.getLogger(ReadFn.class);
+
+ private transient Cluster cluster;
+
+ private transient Session session;
+
+ private transient Read<T> lastRead;
+
+ @ProcessElement
+ public void processElement(@Element Read<T> read, OutputReceiver<T>
receiver) {
+ Session session = getSession(read);
+ Mapper<T> mapper = read.mapperFactoryFn().apply(session);
+ String partitionKey =
+
cluster.getMetadata().getKeyspace(read.keyspace().get()).getTable(read.table().get())
+ .getPartitionKey().stream()
+ .map(ColumnMetadata::getName)
+ .collect(Collectors.joining(","));
+
+ String query = generateRangeQuery(read, partitionKey, read.ringRanges() !=
null);
+ PreparedStatement preparedStatement = session.prepare(query);
+ Set<RingRange> ringRanges =
+ read.ringRanges() == null ? Collections.<RingRange>emptySet() :
read.ringRanges().get();
+
+ for (RingRange rr : ringRanges) {
+ Token startToken =
cluster.getMetadata().newToken(rr.getStart().toString());
+ Token endToken = cluster.getMetadata().newToken(rr.getEnd().toString());
+ ResultSet rs =
+ session.execute(preparedStatement.bind().setToken(0,
startToken).setToken(1, endToken));
+ Iterator<T> iter = mapper.map(rs);
+ while (iter.hasNext()) {
+ T n = iter.next();
+ receiver.output(n);
+ }
+ }
+
+ if (read.ringRanges() == null) {
+ ResultSet rs = session.execute(preparedStatement.bind());
+ Iterator<T> iter = mapper.map(rs);
+ while (iter.hasNext()) {
+ receiver.output(iter.next());
+ }
+ }
+ }
+
+ @Teardown
+ public void teardown() {
+ if (session != null) {
+ this.session.close();
+ }
+ if (cluster != null) {
+ this.cluster.close();
+ }
+ }
+
+ private Session getSession(Read<T> read) {
+ if (cluster == null || !reuseCluster(this.lastRead, read)) {
+ this.cluster =
+ CassandraIO.getCluster(
+ read.hosts(),
+ read.port(),
+ read.username(),
+ read.password(),
+ read.localDc(),
+ read.consistencyLevel());
+ }
+ if (session == null || !reuseSession(lastRead, read)) {
+ this.session = this.cluster.connect(read.keyspace().get());
+ }
+ this.lastRead = read;
+ return this.session;
+ }
+
+ private static <T> boolean reuseCluster(Read<T> readA, Read<T> readB) {
+ return readA != null
Review comment:
I didn't address this yet, wanted your thoughts on it. I agree it can
be improved.
The driver will handle Connection *pooling*, (handling N number of
connections per cassandra host and sharing them in a thread safe way), but we
still need to initiate a `Session` per Cassandra instance, and maintain a
reference to the `Session` to keep those connections in scope (under the hood).
So we could use something as simple as a `Map<?, Cluster>` and `Map<?,
Session>`, but remember we have to do both, since each `Read<>` might be
hitting an entirely different cassandra cluster (hence the need to maintain
different `Cluster` objects as well). If we wanted something fancier, we
could try a guava LRU or something on the off chance the user is initiating
hundreds(thousands/millions?) of different Session objects.
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Issue Time Tracking
-------------------
Worklog Id: (was: 501161)
Time Spent: 15h 10m (was: 15h)
> 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
> Priority: P3
> Time Spent: 15h 10m
> 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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