Segment Fetchers

When pinot segment files are created in external systems (hadoop/spark/etc), there are several ways to push those data to pinot Controller and Server:

1. push segment to shared NFS and let pinot pull segment files from the location of that NFS.

2. push segment to a Web server and let pinot pull segment files from the Web server with http/https link.

3. push segment to HDFS and let pinot pull segment files from HDFS with hdfs location uri.

4. push segment to other system and implement your own segment fetcher to pull data from those systems.

The first two options should be supported out of the box with pinot package. As long your remote jobs send Pinot controller with the corresponding URI to the files it will pick up the file and allocate it to proper Pinot Servers and brokers. To enable Pinot support for HDFS, you will need to provide Pinot Hadoop configuration and proper Hadoop dependencies.

Creating Pinot segments

Pinot segments can be created offline on Hadoop, or via command line from data files. Controller REST endpoint can then be used to add the segment to the table to which the segment belongs. Pinot segments can also be created by ingesting data from realtime resources (such as Kafka).

Creating segments using hadoop

Offline Pinot workflow

To create Pinot segments on Hadoop, a workflow can be created to complete the following steps:

1. Pre-aggregate, clean up and prepare the data, writing it as Avro format files in a single HDFS directory

2. Create segments

3. Upload segments to the Pinot cluster

Step one can be done using your favorite tool (such as Pig, Hive or Spark), Pinot provides two MapReduce jobs to do step two and three.

Configuring the job

Create a job properties configuration file, such as one below:

# === Index segment creation job config ===

# path.to.input: Input directory containing Avro files
path.to.input=/user/pinot/input/data

# path.to.output: Output directory containing Pinot segments
path.to.output=/user/pinot/output

# path.to.schema: Schema file for the table, stored locally
path.to.schema=flights-schema.json

# segment.table.name: Name of the table for which to generate segments
segment.table.name=flights

# === Segment tar push job config ===

# push.to.hosts: Comma separated list of controllers host names to which to push
push.to.hosts=controller_host_0,controller_host_1

# push.to.port: The port on which the controller runs
push.to.port=8888

Executing the job

The Pinot Hadoop module contains a job that you can incorporate into your workflow to generate Pinot segments.

mvn clean install -DskipTests -Pbuild-shaded-jar
hadoop jar pinot-hadoop-<version>-SNAPSHOT-shaded.jar SegmentCreation job.properties

You can then use the SegmentTarPush job to push segments via the controller REST API.

hadoop jar pinot-hadoop-<version>-SNAPSHOT-shaded.jar SegmentTarPush job.properties

Creating Pinot segments outside of Hadoop

Here is how you can create Pinot segments from standard formats like CSV/JSON/AVRO.

1. Follow the steps described in the section on Compiling the code to build pinot. Locate pinot-admin.sh in pinot-tools/target/pinot-tools=pkg/bin/pinot-admin.sh.

2. Create a top level directory containing all the CSV/JSON/AVRO files that need to be converted into segments.

3. The file name extensions are expected to be the same as the format name (i.e .csv, .json or .avro), and are case insensitive. Note that the converter expects the .csv extension even if the data is delimited using tabs or spaces instead.

4. Prepare a schema file describing the schema of the input data. The schema needs to be in JSON format. See example later in this section.

5. Specifically for CSV format, an optional csv config file can be provided (also in JSON format). This is used to configure parameters like the delimiter/header for the CSV file etc. A detailed description of this follows below.

Run the pinot-admin command to generate the segments. The command can be invoked as follows. Options within “[ ]” are optional. For -format, the default value is AVRO.

bin/pinot-admin.sh CreateSegment -dataDir <input_data_dir> [-format [CSV/JSON/AVRO]] [-readerConfigFile <csv_config_file>] [-generatorConfigFile <generator_config_file>] -segmentName <segment_name> -schemaFile <input_schema_file> -tableName <table_name> -outDir <output_data_dir> [-overwrite]

To configure various parameters for CSV a config file in JSON format can be provided. This file is optional, as are each of its parameters. When not provided, default values used for these parameters are described below:

1. fileFormat: Specify one of the following. Default is EXCEL.

   1. EXCEL

   2. MYSQL

   3. RFC4180

   4. TDF

2. header: If the input CSV file does not contain a header, it can be specified using this field. Note, if this is specified, then the input file is expected to not contain the header row, or else it will result in parse error. The columns in the header must be delimited by the same delimiter character as the rest of the CSV file.

3. delimiter: Use this to specify a delimiter character. The default value is “,”.

4. multiValueDelimiter: Use this to specify a delimiter character for each value in multi-valued columns. The default value is “;”.

Below is a sample config file.

{
  "fileFormat": "EXCEL",
  "header": "col1,col2,col3,col4",
  "delimiter": "\t",
  "multiValueDelimiter": ","
}

Sample Schema:

{
  "schemaName": "flights",
  "dimensionFieldSpecs": [
    {
      "name": "flightNumber",
      "dataType": "LONG"
    },
    {
      "name": "tags",
      "dataType": "STRING",
      "singleValueField": false
    }
  ],
  "metricFieldSpecs": [
    {
      "name": "price",
      "dataType": "DOUBLE"
    }
  ],
  "timeFieldSpec": {
    "incomingGranularitySpec": {
      "name": "daysSinceEpoch",
      "dataType": "INT",
      "timeType": "DAYS"
    }
  }
}

Pushing offline segments to Pinot

You can use curl to push a segment to pinot:

curl -X POST -F segment=@<segment-tar-file-path> http://controllerHost:controllerPort/segments

Alternatively you can use the pinot-admin.sh utility to upload one or more segments:

pinot-tools/target/pinot-tools-pkg/bin//pinot-admin.sh UploadSegment -controllerHost <hostname> -controllerPort <port> -segmentDir <segmentDirectoryPath>

The command uploads all the segments found in segmentDirectoryPath. The segments could be either tar-compressed (in which case it is a file under segmentDirectoryPath) or uncompressed (in which case it is a directory under segmentDirectoryPath).

HDFS segment fetcher configs

In your Pinot controller/server configuration, you will need to provide the following configs:

pinot.controller.segment.fetcher.hdfs.hadoop.conf.path=`<file path to hadoop conf folder>

or

pinot.server.segment.fetcher.hdfs.hadoop.conf.path=`<file path to hadoop conf folder>

This path should point the local folder containing core-site.xml and hdfs-site.xml files from your Hadoop installation

pinot.controller.segment.fetcher.hdfs.hadoop.kerberos.principle=`<your kerberos principal>
pinot.controller.segment.fetcher.hdfs.hadoop.kerberos.keytab=`<your kerberos keytab>

or

pinot.server.segment.fetcher.hdfs.hadoop.kerberos.principle=`<your kerberos principal>
pinot.server.segment.fetcher.hdfs.hadoop.kerberos.keytab=`<your kerberos keytab>

These two configs should be the corresponding Kerberos configuration if your Hadoop installation is secured with Kerberos. Please check Hadoop Kerberos guide on how to generate Kerberos security identification.

You will also need to provide proper Hadoop dependencies jars from your Hadoop installation to your Pinot startup scripts.

Push HDFS segment to Pinot Controller

To push HDFS segment files to Pinot controller, you just need to ensure you have proper Hadoop configuration as we mentioned in the previous part. Then your remote segment creation/push job can send the HDFS path of your newly created segment files to the Pinot Controller and let it download the files.

For example, the following curl requests to Controller will notify it to download segment files to the proper table:

curl -X POST -H "UPLOAD_TYPE:URI" -H "DOWNLOAD_URI:hdfs://nameservice1/hadoop/path/to/segment/file.

Implement your own segment fetcher for other systems

You can also implement your own segment fetchers for other file systems and load into Pinot system with an external jar. All you need to do is to implement a class that extends the interface of SegmentFetcher and provides config to Pinot Controller and Server as follows:

pinot.controller.segment.fetcher.`<protocol>`.class =`<class path to your implementation>

or

pinot.server.segment.fetcher.`<protocol>`.class =`<class path to your implementation>

You can also provide other configs to your fetcher under config-root pinot.server.segment.fetcher.<protocol>