Table

A table is a logical abstraction that represents a collection of related data. It is composed of columns and rows (known as documents in Pinot). The columns, data types, and other metadata related to the table are defined using a schema.

Pinot breaks a table into multiple segments and stores these segments in a deep-store such as HDFS as well as Pinot servers.

In the Pinot cluster, a table is modeled as a Helix resource and each segment of a table is modeled as a Helix Partition.

Pinot supports the following types of table:

Type
Description

Offline

Offline tables ingest pre-built pinot-segments from external data stores. This is generally used for batch ingestion.

Realtime

Realtime tables ingest data from streams (such as Kafka) and build segments from the consumed data.

Hybrid

A hybrid Pinot table has both realtime as well as offline tables under the hood. By default, all tables in Pinot are Hybrid in nature.

The user querying the database does not need to know the type of the table. They only need to specify the table name in the query.

e.g. regardless of whether we have an offline table myTable_OFFLINE, a real-time table myTable_REALTIME, or a hybrid table containing both of these, the query will be:

select count(*)
from myTable

Table Configuration is used to define the table properties, such as name, type, indexing, routing, retention etc. It is written in JSON format and is stored in Zookeeper, along with the table schema.

You can use the following properties to make your tables faster or leaner:

  • Segment

  • Indexing

  • Tenants

Segments

A table is comprised of small chunks of data. These chunks are known as Segments. To learn more about how Pinot creates and manages segments see the official documentation

For offline tables, Segments are built outside of pinot and uploaded using a distributed executor such as Spark or Hadoop. For more details, see Batch Ingestion.

For real-time tables, segments are built in a specific interval inside Pinot. You can tune the following for the real-time segments:

Flush

The Pinot real-time consumer ingests the data, creates the segment, and then flushes the in-memory segment to disk. Pinot allows you to configure when to flush the segment in the following ways:

  • Number of consumed rows - After consuming X no. of rows from the stream, Pinot will persist the segment to disk

  • Number of desired rows per segment - Pinot learns and then estimates the number of rows that need to be consumed so that the persisted segment is approximately the size. The learning phase starts by setting the number of rows to 100,000 (this value can be changed) and adjusts it to reach the desired segment size. The segment size may go significantly over the desired size during the learning phase. Pinot corrects the estimation as it goes along, so it is not guaranteed that the resulting completed segments are of the exact size as configured. You should set this value to optimize the performance of queries.

  • Max time duration to wait - Pinot consumers wait for the configured time duration after which segments are persisted to the disk.

Replicas A segment can have multiple replicas to provide higher availability. You can configure the number of replicas for a table segment using

Completion Mode By default, if the in-memory segment in the non-winner server is equivalent to the committed segment, then the non-winner server builds and replaces the segment. If the available segment is not equivalent to the committed segment, the server simply downloads the committed segment from the controller.

However, in certain scenarios, the segment build can get very memory intensive. It might be desirable to enforce the non-committer servers to just download the segment from the controller, instead of building it again. You can do this by setting completionMode: "DOWNLOAD" in the table configuration

For more details on why this is needed, see Completion Config

Download Scheme

A Pinot server may fail to download segments from the deep store such as HDFS after its completion. However, you can configure servers to download these segments from peer servers instead of the deep store. Currently, only HTTP and HTTPS download schemes are supported. More methods such as gRPC/Thrift can be added in the future.

For more details about peer segment download during real-time ingestion, please refer to this design doc on bypass deep store for segment completion.

Indexing

You can create multiple indices on a table to increase the performance of the queries. The following types of indices are supported:

For more details on each indexing mechanism and corresponding configurations, see Indexing.

You can also set up Bloomfilters on columns to make queries faster. Further, you can also keep segments in off-heap instead of on-heap memory for faster queries.

Pre-aggregation

You can aggregate the real-time stream data as it is consumed to reduce segment sizes. We sum the metric column values of all rows that have the same values for all dimension and time columns and create a single row in the segment. This feature is only available on REALTIME tables.

The only supported aggregation is SUM. The columns on which pre-aggregation is to be done need to satisfy the following requirements:

  • All metrics should be listed in noDictionaryColumns .

  • There should not be any multi-value dimensions.

  • All dimension columns are treated to have a dictionary, even if they appear as noDictionaryColumns in the config.

The following table config snippet shows an example of enabling pre-aggregation during real-time ingestion.

pinot-table-realtime.json
    "tableIndexConfig": { 
      "noDictionaryColumns": ["metric1", "metric2"],
      "aggregateMetrics": true,
      ...
    }

Tenants

Each table is associated with a tenant. A segment resides on the server, which has the same tenant as itself. For more details on how tenants work, see Tenant.

You can also override if a table should move to a server with different tenant based on segment status.

A tagOverrideConfig can be added under the tenants section for realtime tables, to override tags for consuming and completed segments. For example:

  "broker": "brokerTenantName",
  "server": "serverTenantName",
  "tagOverrideConfig" : {
    "realtimeConsuming" : "serverTenantName_REALTIME"
    "realtimeCompleted" : "serverTenantName_OFFLINE"
  }
}

In the above example, the consuming segments will still be assigned to serverTenantName_REALTIME hosts, but once they are completed, the segments will be moved to serverTeantnName_OFFLINE. It is possible to specify the full name of any tag in this section (so, for example, you could decide that completed segments for this table should be in pinot servers tagged as allTables_COMPLETED). To learn more about this config, see the Moving Completed Segments section.

Hybrid Table

A hybrid table is a table composed of 2 tables, one offline and one real-time that share the same name. In such a table, offline segments may be pushed periodically. The retention on the offline table can be set to a high value since segments are coming in on a periodic basis, whereas the retention on the real-time part can be small.

Once an offline segment is pushed to cover a recent time period, the brokers automatically switch to using the offline table for segments for that time period and use the real-time table only for data not available in the offline table.

To understand how time boundary works in the case of a hybrid table, see Broker.

A typical scenario is pushing a deduped cleaned up data into an offline table every day while consuming real-time data as and when it arrives. The data can be kept in offline tables for even a few years while the real-time data would be cleaned every few days.

Examples

Create a table config for your data, or see examples for all possible batch/streaming tables.

Prerequisites

  1. Setup the cluster

  2. Create broker and server tenants

Offline Table Creation

docker run \
    --network=pinot-demo \
    --name pinot-batch-table-creation \
    ${PINOT_IMAGE} AddTable \
    -schemaFile examples/batch/airlineStats/airlineStats_schema.json \
    -tableConfigFile examples/batch/airlineStats/airlineStats_offline_table_config.json \
    -controllerHost pinot-controller \
    -controllerPort 9000 \
    -exec

Sample Console Output

Executing command: AddTable -tableConfigFile examples/batch/airlineStats/airlineStats_offline_table_config.json -schemaFile examples/batch/airlineStats/airlineStats_schema.json -controllerHost pinot-controller -controllerPort 9000 -exec
Sending request: http://pinot-controller:9000/schemas to controller: a413b0013806, version: Unknown
{"status":"Table airlineStats_OFFLINE succesfully added"}

Check out the table config in the Rest API to make sure it was successfully uploaded.

Streaming Table Creation

Start Kafka

docker run \
    --network pinot-demo --name=kafka \
    -e KAFKA_ZOOKEEPER_CONNECT=pinot-zookeeper:2181/kafka \
    -e KAFKA_BROKER_ID=0 \
    -e KAFKA_ADVERTISED_HOST_NAME=kafka \
    -d wurstmeister/kafka:latest

Create a Kafka Topic

docker exec \
  -t kafka \
  /opt/kafka/bin/kafka-topics.sh \
  --zookeeper pinot-zookeeper:2181/kafka \
  --partitions=1 --replication-factor=1 \
  --create --topic flights-realtime

Create a Streaming table

docker run \
    --network=pinot-demo \
    --name pinot-streaming-table-creation \
    ${PINOT_IMAGE} AddTable \
    -schemaFile examples/stream/airlineStats/airlineStats_schema.json \
    -tableConfigFile examples/docker/table-configs/airlineStats_realtime_table_config.json \
    -controllerHost pinot-controller \
    -controllerPort 9000 \
    -exec

Sample output

Executing command: AddTable -tableConfigFile examples/docker/table-configs/airlineStats_realtime_table_config.json -schemaFile examples/stream/airlineStats/airlineStats_schema.json -controllerHost pinot-controller -controllerPort 9000 -exec
Sending request: http://pinot-controller:9000/schemas to controller: 8fbe601012f3, version: Unknown
{"status":"Table airlineStats_REALTIME succesfully added"}

Check out the table config in the Rest API to make sure it was successfully uploaded.

Hybrid Table creation

"OFFLINE": {
    "tableName": "pinotTable", 
    "tableType": "OFFLINE", 
    "segmentsConfig": {
      ... 
    }, 
    "tableIndexConfig": { 
      ... 
    },  
    "tenants": {
      "broker": "myBrokerTenant", 
      "server": "myServerTenant"
    },
    "metadata": {
      ...
    }
  },
  "REALTIME": { 
    "tableName": "pinotTable", 
    "tableType": "REALTIME", 
    "segmentsConfig": {
      ...
    }, 
    "tableIndexConfig": { 
      ... 
      "streamConfigs": {
        ...
      },  
    },  
    "tenants": {
      "broker": "myBrokerTenant", 
      "server": "myServerTenant"
    },
    "metadata": {
    ...
    }
  }
}

Note that creating a hybrid table has to be done in 2 separate steps of creating an offline and real-time table individually.

PreviousSchemaNextSegment

Last updated