Stocator - Storage Connector for Apache Spark

Apache Spark can work with multiple data sources that include various object stores like IBM Cloud Object Storage, OpenStack Swift and more. To access an object store, Apache Spark uses Hadoop modules that contain connectors to the various object stores.

Apache Spark needs only small set of object store functionalities. Specifically, Apache Spark requires object listing, objects creation, read objects, and getting data partitions. Hadoop connectors, however, must be compliant with the Hadoop ecosystem. This means they support many more operations, such as shell operations on directories, including move, copy, rename, etc. (these are not native object store operations). Moreover, Hadoop Map Reduce Client is designed to work with file systems and not object stores. The temp files and folders it uses for every write operation are renamed, copied, and deleted. This leads to dozens of useless requests targeted at the object store. It’s clear that Hadoop is designed to work with file systems and not object stores.

Stocator is implicitly designed for the object stores, it has very a different architecture from the existing Hadoop connector. It doesn’t depends on the Hadoop modules and interacts directly with object stores.

Stocator is a generic connector, that may contain various implementations for object stores. It shipped with OpenStack Swift and IBM Cloud Object Storage connectors. Stocator can be easily extended with more object store implementations.

Major features

Stocator build procedure

Usage with Apache Spark

Stocator can be used easily with Apache Spark. There are different ways to use Stocator

Using spark-packages

Stocator deployed on spark-packages. This is the easiest form to integrate Stocator in Spark. Just follow stocator

Using Stocator without compiling Apache Spark

It is possible to execute Apache Spark with Stocator, without compiling Apache Spark. Just make sure that Stocator jars on the class path. Build Stocator with 

    mvn clean package -Pall-in-one

Directory stocator/target contains standalone jar stocator-X.Y.Z-jar-with-dependencies.jar.

The best is to extend Spark's class path to include Stocator jar. Edit conf/spark-defaults.conf and add Stocator to the class path. For example

spark.driver.extraClassPath=/<PATH>/stocator/target/stocator-X-Y-Z-jar-with-dependencies.jar
spark.executor.extraClassPath=/<PATH>/stocator/target/stocator-X-Y-Z-jar-with-dependencies.jar

Another option is to run Apache Spark with 

./bin/spark-shell --jars stocator-X.Y.Z-jar-with-dependencies.jar

However this is less adviced, as Spark will copy Stocator jar to the executors, which may consume time.

Using Stocator with Apache Spark compilation

Less recommended, only for advanced users who want to recompile Spark. Both main pom.xml and core/pom.xml of Spark should be modified. add to the <properties> of the main pom.xml

<stocator.version>X.Y.Z</stocator.version>

add stocator dependency to the main pom.xml

 <dependency>
      <groupId>com.ibm.stocator</groupId>
      <artifactId>stocator</artifactId>
      <version>${stocator.version}</version>
      <scope>${hadoop.deps.scope}</scope>
  </dependency>

modify core/pom.xml to include stocator

<dependency>
      <groupId>com.ibm.stocator</groupId>
      <artifactId>stocator</artifactId>
 </dependency>

Compile Apache Spark with Haddop support as described here

General requirements

Stocator verifies that 

mapreduce.fileoutputcommitter.marksuccessfuljobs=true

If not modified, the default value of mapreduce.fileoutputcommitter.marksuccessfuljobs is true.

Configuration keys

Stocator uses configuration keys that can be configured via spark's core-site.xml or provided in run time without using core-site.xml. To provide keys in run time use SparkContext variable with

sc.hadoopConfiguration.set("KEY","VALUE")

For usage with core-site.xml, see the configuration template located under conf/core-site.xml.template.

Stocator and IBM Cloud Object Storage (IBM COS)

Stocator allows to access IBM Cloud Object Storage via cos:// schema. The general URI is the form

cos://<bucket>.<service>/object(s)

where bucket is object storage bucket and <service> identifies configuration group entry.

Using multiple service names

Each <service> may be any text, without special characters. Each service may use it's specific credentials and has different endpoint. By using multiple <service> allows to use different endpoints simultaneously.

For example, service=myObjectStore, then URI will be of the form

cos://<bucket>.myObjectStore/object(s)

and configuration keys will have prefix fs.cos.myObjectStore. If none provided, the default value is service, e.g.

cos://<bucket>.service/object(s)

and configuration keys will have prefix fs.cos.service.

Reference Stocator in the core-site.xml

Configure Stocator in conf/core-site.xml

<property>
    <name>fs.stocator.scheme.list</name>
    <value>cos</value>
</property>
<property>
    <name>fs.cos.impl</name>
    <value>com.ibm.stocator.fs.ObjectStoreFileSystem</value>
</property>
<property>
    <name>fs.stocator.cos.impl</name>
    <value>com.ibm.stocator.fs.cos.COSAPIClient</value>
</property>
<property>
    <name>fs.stocator.cos.scheme</name>
    <value>cos</value>
</property>

Configuration keys

Stocator COS connector expose "fs.cos." keys prefix. For backward compatibility Stocator also supports "fs.s3d" and "fs.s3a" prefix, where "fs.cos" has the highest priority and will overwrite other keys, if present.

COS Connector configuration with IAM

To work with IAM and provide api key please switch to the relevant ibm-sdk branch depends on the Stocator version you need. For example for Stocator 1.0.24 release, switch to 1.0.24-ibm-sdk, for Stocator master 1.0.25-SNAPSHOT, switch to 1.0.25-SNAPSHOT-IBM-SDK and so on.

You will need to build Stocator manually, for example using 1.0.24-ibm-sdk branch:

git clone https://github.com/SparkTC/stocator
cd stocator
git fetch
git checkout -b 1.0.24-ibm-sdk origin/1.0.24-ibm-sdk
mvn clean install –DskipTests

You now need to include the target/stocator-1.0.24-SNAPSHOT-IBM-SDK.jar into class path of Spark. Follow section Using Stocator without compiling Apache Spark

Configure Stocator

The next step if to configure Stocator with your COS credentials. The COS credentials is of the form

{
  "apikey": "123",
  "endpoints": "https://cos-service.bluemix.net/endpoints",
  "iam_apikey_description": "Auto generated apikey during resource-key operation for Instance - abc",
  "iam_apikey_name": "auto-generated-apikey-123",
  "iam_role_crn": "role",
  "iam_serviceid_crn": "identity-123::serviceid:ServiceId-XYZ",
  "resource_instance_id": "abc"
}

The following is the list of the Stocator configuration keys. <service> can be any value, for example myCOS

Key Info Mandatory value
fs.cos.<service>.iam.api.key API key mandatory value of apiKey
fs.cos.<service>.iam.service.id Service ID mandatory Value of iam_serviceid_crn. In certain cases you need only value after :serviceid:
fs.cos.<service>.endpoint COS endpoint mandatory Open link from endpoints and choose relevant endpoint. This endpoint should go here

Example, configure <service> as myCOS:

<property>
    <name>fs.cos.myCos.iam.api.key</name>
    <value>123</value>
</property>
<property>
    <name>fs.cos.myCos.endpoint</name>
    <value>http://s3-api.us-geo.objectstorage.softlayer.net</value>
</property>
<property>
    <name>fs.cos.myCos.iam.service.id</name>
    <value>ServiceId-XYZ</value>
</property>

Now you can use URI

cos://mybucket.myCos/myobject(s)

An optional, it is possible to provide existing token instead of using API key. Instead of providing fs.cos.myCos.iam.api.key, Stocator supports fs.cos.myCos.iam.api.token that may contain value of the existing token. When token is expired, Stocator will throw 403 exception. It's the user responsibility to provide long activation token or re-create token outside of Stocator.

COS Connector configuration without IAM

The following is the list of the configuration keys. <service> can be any value, for example myCOS

Key Info Mandatory
fs.cos.<service>.access.key Access key mandatory
fs.cos.<service>.secret.key Secret key mandatory
fs.cos.<service>.endpoint COS endpoint mandatory
fs.cos.<service>.v2.signer.type Signer type optional

Example, configure <service> as myCOS:

<property>
    <name>fs.cos.myCos.access.key</name>
    <value>ACCESS KEY</value>
</property>
<property>
    <name>fs.cos.myCos.endpoint</name>
    <value>http://s3-api.us-geo.objectstorage.softlayer.net</value>
</property>
<property>
    <name>fs.cos.myCos.secret.key</name>
    <value>SECRET KEY</value>
</property>
<property>
    <name>fs.cos.myCos.v2.signer.type</name>
    <value>false</value>
</property>

Now you can use URI

cos://mybucket.myCos/myobject(s)

COS Connector optional configuration tuning

Key Default Info
fs.cos.socket.send.buffer 8*1024 socket send buffer to be used in the client
fs.cos.socket.recv.buffer 8*1024 socket send buffer to be used in the client
fs.cos.paging.maximum 5000 number of records to get while paging through a directory listing
fs.cos.threads.max 10 the maximum number of threads to allow in the pool used by TransferManager
fs.cos.threads.keepalivetime 60 the time an idle thread waits before terminating
fs.cos.signing-algorithm override signature algorithm used for signing requests
fs.cos.connection.maximum 10000 number of simultaneous connections to the object store
fs.cos.attempts.maximum 20 number of times we should retry errors
fs.cos.block.size 128 size of a block in MB
fs.cos.connection.timeout 800000 amount of time (in ms) until we give up on a connection to the object store
fs.cos.connection.establish.timeout 50000 amount of time (in ms) until we give up trying to establish a connection to the object store
fs.cos.client.execution.timeout 500000 amount of time (in ms) to allow a client to complete the execution of an API call
fs.cos.client.request.timeout 500000 amount of time to wait (in ms) for a request to complete before giving up and timing out
fs.cos.connection.ssl.enabled true Enables or disables SSL connections to COS
fs.cos.proxy.host Hostname of the (optional) proxy server for COS connections
fs.cos.proxy.port Proxy server port. If this property is not set but fs.cos.proxy.host is, port 80 or 443 is assumed (consistent with the value of fs.cos.connection.ssl.enabled)
fs.cos.proxy.username Username for authenticating with proxy server
fs.cos.proxy.password Password for authenticating with proxy server
fs.cos.proxy.domain Domain for authenticating with proxy server
fs.cos.user.agent.prefix User agent prefix
fs.cos.flat.list true In flat listing the result will include all objects under specific path prefix, for example bucket/a/b/data.txt, bucket/a/d.data. If listed bucket/a*, then result will include both objects. If flat list is set to flase, then it contains the same list behaviour as community s3a connector.
fs.stocator.cache.size 2000 The Guava cache size used by the COS connector
fs.cos.multipart.size 8388608 Size in bytes. Define multipart size
fs.cos.multipart.threshold Max Integer minimum size in bytes before we start a multipart uploads, default is max integer
fs.cos.fast.upload false enable or disable block upload
fs.stocator.glob.bracket.support false if true supports Hadoop string patterns of the form {ab,c{de, fh}}. Due to possible collision with object names, this mode prevents from create an object whose name contains {}
fs.cos.atomic.write false enable or disable atomic write to COS using Etags. Atomic write is available only when the write is done in one chunk.
When the flagfs.cos.fast.upload is set to false atomic write will be available only for write that is lower or equal to fs.cos.multipart.threshold size.
When the flag fs.cos.fast.upload is set to true atomic write will be available only for write that require only one block.

Stocator and Object Storage based on OpenStack Swift API

Stocator allows to access OpenStack Swift API based object stores via unique schema swift2d://.

Configure Stocator in the core-site.xml

Add the dependence to Stocator in conf/core-site.xml

<property>
    <name>fs.stocator.scheme.list</name>
    <value>swift2d</value>
</property>

If Swift connector used concurrently with COS connector, then also configure 

<property>
    <name>fs.stocator.scheme.list</name>
    <value>swift2d,cos</value>
</property>

Configure the rest of the keys

<property>
    <name>fs.swift2d.impl</name>
    <value>com.ibm.stocator.fs.ObjectStoreFileSystem</value>
</property>
<property>
    <name>fs.stocator.swift2d.impl</name>
    <value>com.ibm.stocator.fs.swift.SwiftAPIClient</value>
</property>
<property>
    <name>fs.stocator.swift2d.scheme</name>
    <value>swift2d</value>
</property>

Swift connector configuration

The following is the list of the configuration keys

Key Info Default value
fs.swift2d.service.SERVICE_NAME.auth.url Mandatory
fs.swift2d.service.SERVICE_NAME.public Optional. Values: true, false false
fs.swift2d.service.SERVICE_NAME.tenant Mandatory
fs.swift2d.service.SERVICE_NAME.password Mandatory
fs.swift2d.service.SERVICE_NAME.username Mandatory
fs.swift2d.service.SERVICE_NAME.block.size Block size in MB 128MB
fs.swift2d.service.SERVICE_NAME.region Mandatory for Keystone
fs.swift2d.service.SERVICE_NAME.auth.method Optional. Values: keystone, swiftauth, keystoneV3 keystoneV3
fs.swift2d.service.SERVICE_NAME.nonstreaming.upload Optional. If set to true then any object upload will be stored locally in the temp file and uploaded on close method. Disable stocator streaming mode false

Example of core-site.xml keys

Keystone V2
<property>
   <name>fs.swift2d.service.SERVICE_NAME.auth.url</name>
    <value>http://IP:PORT/v2.0/tokens</value>
</property>
<property>
   <name>fs.swift2d.service.SERVICE_NAME.public</name>
    <value>true</value>
</property>
<property>
   <name>fs.swift2d.service.SERVICE_NAME.tenant</name>
    <value>TENANT</value>
</property>
<property>
   <name>fs.swift2d.service.SERVICE_NAME.password</name>
    <value>PASSWORD</value>
</property>
<property>
   <name>fs.swift2d.service.SERVICE_NAME.username</name>
    <value>USERNAME</value>
</property>
<property>
   <name>fs.swift2d.service.SERVICE_NAME.auth.method</name>
   <!-- swiftauth if needed -->
    <value>keystone</value>
</property>

Keystone V3 mapping to keys

Driver configuration key Keystone V3 key
fs.swift2d.service.SERVICE_NAME.username user id
fs.swift2d.service.SERVICE_NAME.tenant project id 
<property>
    <name>fs.swift2d.service.SERVICE_NAME.auth.url</name>
    <value>https://identity.open.softlayer.com/v3/auth/tokens</value>
</property>
<property>
    <name>fs.swift2d.service.SERVICE_NAME.public</name>
    <value>true</value>
</property>
<property>
    <name>fs.swift2d.service.SERVICE_NAME.tenant</name>
    <value>PROJECTID</value>
</property>
<property>
    <name>fs.swift2d.service.SERVICE_NAME.password</name>
    <value>PASSWORD</value>
</property>
<property>
    <name>fs.swift2d.service.SERVICE_NAME.username</name>
    <value>USERID</value>
</property>
<property>
    <name>fs.swift2d.service.SERVICE_NAME.auth.method</name>
    <value>keystoneV3</value>
</property>
<property>
    <name>fs.swift2d.service.SERVICE_NAME.region</name>
    <value>dallas</value>
</property>

Swift connector optional configuration

Below is the optional configuration that can be provided to Stocator and used internally to configure HttpClient.

Configuration key Default Info
fs.stocator.MaxPerRoute 25 maximal connections per IP route
fs.stocator.MaxTotal 50 maximal concurrent connections
fs.stocator.SoTimeout 1000 low level socket timeout in milliseconds
fs.stocator.executionCount 100 number of retries for certain HTTP issues
fs.stocator.ReqConnectTimeout 5000 Request level connect timeout. Determines the timeout in milliseconds until a connection is established
fs.stocator.ReqConnectionRequestTimeout 5000 Request level connection timeout. Returns the timeout in milliseconds used when requesting a connection from the connection manager
fs.stocator.ReqSocketTimeout 5000 Defines the socket timeout (SO_TIMEOUT) in milliseconds, which is the timeout for waiting for data or, put differently, a maximum period inactivity between two consecutive data packets).
fs.stocator.joss.synchronize.time false Will disable JOSS to synchronize time with the server. Setting this value to 'false' will badly impact on temp url. However this will reduce HEAD on account which might be problematic if the user doesn't has access rights to HEAD an account
fs.stocator.tls.version false if not provided, then system choosen is the default. In certain cases user may setup custom value, like TLSv1.2

Configure Stocator's schemas (optional)

By default Stocator exposes swift2d:// for Swift API and cos:// for IBM Cloud Object Storage. It possible to configure Stocator to expose different schema.

The following example, will configure Stocator to respond to swift:// in addition to swift2d://. This is useful, so users doesn't need to modify existing jobs that already uses hadoop-openstack connector. Below the example, how to configure Stocator to respond both to swift:// and swift2d://

<property>
    <name>fs.stocator.scheme.list</name>
    <value>swift2d,swift</value>
</property>
<!-- configure stocator as swift2d:// -->
<property>
    <name>fs.swift2d.impl</name>
    <value>com.ibm.stocator.fs.ObjectStoreFileSystem</value>
</property>
<property>
    <name>fs.stocator.swift2d.impl</name>
    <value>com.ibm.stocator.fs.swift.SwiftAPIClient</value>
</property>
<property>
    <name>fs.stocator.swift2d.scheme</name>
    <value>swift2d</value>
</property>
<!-- configure stocator as swift:// -->
<property>
    <name>fs.swift.impl</name>
    <value>com.ibm.stocator.fs.ObjectStoreFileSystem</value>
</property>
<property>
    <name>fs.stocator.swift.impl</name>
    <value>com.ibm.stocator.fs.swift.SwiftAPIClient</value>
</property>
<property>
    <name>fs.stocator.swift.scheme</name>
    <value>swift</value>
</property>

Examples

Persists results in IBM Cloud Object Storage

val data = Array(1, 2, 3, 4, 5, 6, 7, 8)
val distData = sc.parallelize(data)
distData.saveAsTextFile("cos://mybucket.service/one1.txt")

Listing bucket mydata directly with a REST client will display

one1.txt
one1.txt/_SUCCESS
one1.txt/part-00000-taskid
one1.txt/part-00001-taskid
one1.txt/part-00002-taskid
one1.txt/part-00003-taskid
one1.txt/part-00004-taskid
one1.txt/part-00005-taskid
one1.txt/part-00006-taskid
one1.txt/part-00007-taskid

Using dataframes

val squaresDF = spark.sparkContext.makeRDD(1 to 5).map(i => (i, i * i)).toDF("value","square")
squaresDF.write.format("parquet").save("cos://mybucket.service/data.parquet")

Running Terasort

Follow 

https://github.com/ehiggs/spark-terasort

Setup Stocator with COS as previosuly explained. In the example we use bucket teradata and service =service

Step 1:

export MAVEN_OPTS="-Xmx2g -XX:MaxPermSize=512M -XX:ReservedCodeCacheSize=512m"

Step 2:

./bin/spark-submit --driver-memory 2g --class com.github.ehiggs.spark.terasort.TeraGen /spark-terasort/target/spark-terasort-1.1-SNAPSHOT-jar-with-dependencies.jar 1g cos://teradata.service/terasort_in

Step 3:

./bin/spark-submit --driver-memory 2g --class com.github.ehiggs.spark.terasort.TeraSort /target/spark-terasort-1.1-SNAPSHOT-jar-with-dependencies.jar 1g cos://teradata.service/terasort_in cos://teradata.service/terasort_out

Step 4:

./bin/spark-submit --driver-memory 2g --class com.github.ehiggs.spark.terasort.TeraValidate /target/spark-terasort-1.1-SNAPSHOT-jar-with-dependencies.jar cos://teradata.service/terasort_out cos://teradata.service/terasort_validate

Functional tests

Copy 

src/test/resources/core-site.xml.tempate to src/test/resources/core-site.xml

Edit src/test/resources/core-site.xml and configure Swift access details. Functional tests will use container from fs.swift2d.test.uri. To use different container, change drivertest to different name. Container need not to be exists in advance and will be created automatically.

How to develop code

If you like to work on code, you can easily setup Eclipse project via

mvn eclipse:eclipse

and import it into Eclipse workspace.

To ease the debugging process, Please modify conf/log4j.properties to

log4j.logger.com.ibm.stocator=ALL

Before you sumit your pull request

We ask that you include a line similar to the following as part of your pull request comments: 

“DCO 1.1 Signed-off-by: Random J Developer“. 
“DCO” stands for “Developer Certificate of Origin,”

and refers to the same text used in the Linux Kernel community. By adding this simple comment, you tell the community that you wrote the code you are contributing, or you have the right to pass on the code that you are contributing.

Need more information?

Stocator Mailing list

Join Stocator mailing list by sending email to [email protected]. Use [email protected] to post questions.

Additional resources

Please follow our wiki for more details. More information about Stocator can be find at

This research was supported by IOStack, an H2020 project of the EU Commission