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EpochCoordinator RPC Endpoint

EpochCoordinator is a ThreadSafeRpcEndpoint that tracks offsets and epochs (coordinates epochs) by handling <> (in <> and <> modes) from...FIXME

EpochCoordinator is <> (using <> factory method) when ContinuousExecution is requested to <>.

[[messages]] [[EpochCoordinatorMessage]] .EpochCoordinator RPC Endpoint's Messages [cols="30m,70",options="header",width="100%"] |=== | Message | Description

a| CommitPartitionEpoch

  • [[CommitPartitionEpoch-partitionId]] Partition ID
  • [[CommitPartitionEpoch-epoch]] Epoch
  • [[CommitPartitionEpoch-message]] DataSource API V2's WriterCommitMessage

| [[CommitPartitionEpoch]] Sent out (in one-way asynchronous mode) exclusively when ContinuousWriteRDD is requested to <> (after all rows were written down to a streaming sink)

| GetCurrentEpoch | [[GetCurrentEpoch]] Sent out (in request-response synchronous mode) exclusively when EpochMarkerGenerator thread is requested to <>

| IncrementAndGetEpoch | [[IncrementAndGetEpoch]] Sent out (in request-response synchronous mode) exclusively when ContinuousExecution is requested to <> (and start a separate epoch update thread)

a| ReportPartitionOffset

  • [[ReportPartitionOffset-partitionId]] Partition ID
  • [[ReportPartitionOffset-epoch]] Epoch
  • [[ReportPartitionOffset-offset]] PartitionOffset

| [[ReportPartitionOffset]] Sent out (in one-way asynchronous mode) exclusively when ContinuousQueuedDataReader is requested for the <> to be read in the current epoch, and the epoch is done

a| SetReaderPartitions

  • [[SetReaderPartitions-numPartitions]] Number of partitions

| [[SetReaderPartitions]] Sent out (in request-response synchronous mode) exclusively when DataSourceV2ScanExec leaf physical operator is requested for the input RDDs (for a <> and is about to create a <>)

The <> is exactly the number of InputPartitions from the ContinuousReader.

a| SetWriterPartitions

  • [[SetWriterPartitions-numPartitions]] Number of partitions

| [[SetWriterPartitions]] Sent out (in request-response synchronous mode) exclusively when WriteToContinuousDataSourceExec leaf physical operator is requested to <> (and requests a <> to collect that simply never finishes...and that's the trick of continuous mode)

a| StopContinuousExecutionWrites | [[StopContinuousExecutionWrites]] Sent out (in request-response synchronous mode) exclusively when ContinuousExecution is requested to <> (and it finishes successfully or not)

|===

[[logging]] [TIP] ==== Enable ALL logging level for org.apache.spark.sql.execution.streaming.continuous.EpochCoordinatorRef* logger to see what happens inside.

Add the following line to conf/log4j.properties:

log4j.logger.org.apache.spark.sql.execution.streaming.continuous.EpochCoordinatorRef*=ALL

Refer to <>.

=== [[receive]] Receiving Messages (Fire-And-Forget One-Way Mode) -- receive Method

[source, scala]

receive: PartialFunction[Any, Unit]

NOTE: receive is part of the RpcEndpoint Contract in Apache Spark to receive messages in fire-and-forget one-way mode.

receive handles the following messages:

  • <>
  • <>

With the <> turned on, receive simply swallows messages and does nothing.

=== [[receiveAndReply]] Receiving Messages (Request-Response Two-Way Mode) -- receiveAndReply Method

[source, scala]

receiveAndReply(context: RpcCallContext): PartialFunction[Any, Unit]

NOTE: receiveAndReply is part of the RpcEndpoint Contract in Apache Spark to receive and reply to messages in request-response two-way mode.

receiveAndReply handles the following messages:

  • <>
  • <>
  • <>
  • <>
  • <>

==== [[resolveCommitsAtEpoch]] resolveCommitsAtEpoch Internal Method

[source, scala]

resolveCommitsAtEpoch(epoch: Long): Unit

resolveCommitsAtEpoch...FIXME

NOTE: resolveCommitsAtEpoch is used exclusively when EpochCoordinator is requested to handle <> and <> messages.

==== [[commitEpoch]] commitEpoch Internal Method

[source, scala]

commitEpoch( epoch: Long, messages: Iterable[WriterCommitMessage]): Unit


commitEpoch...FIXME

NOTE: commitEpoch is used exclusively when EpochCoordinator is requested to <>.

Creating Instance

EpochCoordinator takes the following to be created:

  • [[reader]] <>
  • [[query]] <>
  • [[startEpoch]] Start epoch
  • [[session]] SparkSession
  • [[rpcEnv]] RpcEnv

EpochCoordinator initializes the <>.

=== [[create]] Registering EpochCoordinator RPC Endpoint -- create Factory Method

[source, scala]

create( writer: StreamWriter, reader: ContinuousReader, query: ContinuousExecution, epochCoordinatorId: String, startEpoch: Long, session: SparkSession, env: SparkEnv): RpcEndpointRef


create simply <> and requests the RpcEnv to register a RPC endpoint as EpochCoordinator-[id] (where id is the given epochCoordinatorId).

create prints out the following INFO message to the logs:

Registered EpochCoordinator endpoint

NOTE: create is used exclusively when ContinuousExecution is requested to <>.

=== [[internal-properties]] Internal Properties

[cols="30m,70",options="header",width="100%"] |=== | Name | Description

| queryWritesStopped | [[queryWritesStopped]] Flag that indicates whether to drop messages (true) or not (false) when requested to <>

Default: false

Turned on (true) when requested to <> |===