From implementation or logic complication perspective, the AT_LEAST_ONCE is
somehow simpler compared with EXACTLY_ONCE w/o unaligned, since
it can always process data without blocking any channels.
------------------------------------------------------------------
From:Lu Weizheng <luweizhen...@hotmail.com>
Send Time:2020年6月22日(星期一) 10:53
To:Zhijiang <wangzhijiang...@aliyun.com>; user@flink.apache.org
<user@flink.apache.org>
Subject:回复: Unaligned Checkpoint and Exactly Once
Thank you Zhijiang! The second question about config is just because I find a
method in InputProcessorUtil. I guess AT_LEAST_ONCE mode is a simpler way to
handle checkpont barrier?
private static CheckpointBarrierHandler createCheckpointBarrierHandler(
StreamConfig config,
InputGate[] inputGates,
SubtaskCheckpointCoordinator checkpointCoordinator,
String taskName,
AbstractInvokable toNotifyOnCheckpoint) {
switch (config.getCheckpointMode()) {
case EXACTLY_ONCE:
if (config.isUnalignedCheckpointsEnabled()) {
return new AlternatingCheckpointBarrierHandler(
new CheckpointBarrierAligner(taskName, toNotifyOnCheckpoint,
inputGates),
new CheckpointBarrierUnaligner(checkpointCoordinator, taskName,
toNotifyOnCheckpoint, inputGates),
toNotifyOnCheckpoint);
}
return new CheckpointBarrierAligner(taskName, toNotifyOnCheckpoint,
inputGates);
case AT_LEAST_ONCE:
int numInputChannels =
Arrays.stream(inputGates).mapToInt(InputGate::getNumberOfInputChannels).sum();
return new CheckpointBarrierTracker(numInputChannels,
toNotifyOnCheckpoint);
default:
throw new UnsupportedOperationException("Unrecognized Checkpointing
Mode: " + config.getCheckpointMode());
}
}
发件人: Zhijiang <wangzhijiang...@aliyun.com>
发送时间: 2020年6月22日 10:41
收件人: Lu Weizheng <luweizhen...@hotmail.com>; user@flink.apache.org
<user@flink.apache.org>
主题: Re: Unaligned Checkpoint and Exactly Once
Hi Weizheng,
The unaligned checkpoint (UC) only supports exactly-once mode in Flink 1.11
except savepoint mode. The savepoint is probably used in job rescaling
scenario and we plan to support it in future release version. Of course UC can
satisfy exactly-once semantic as promised.
Regarding the config issue, i am not sure I get your point here. The first
config is for describing whether the current setting mode (actually only
exactly-once) enables UC or not, and the second config is for setting the
different mode (exactly-once or at least-once). I guess you refer to merge them
by using the first config form. But somehow they seem two different dimensions
for config the checkpoint. One is for the semantic of data processing
guarantee. And the other is for how we realize two different mechanisms to
guarantee one (exactly-once) of the semantics.
Best,
Zhijiang
------------------------------------------------------------------
From:Lu Weizheng <luweizhen...@hotmail.com>
Send Time:2020年6月22日(星期一) 07:20
To:user@flink.apache.org <user@flink.apache.org>
Subject:Unaligned Checkpoint and Exactly Once
Hi there,
The new feature in Flink 1.11 will provide us the Unaligned Checkpoint which
means a operator subtask does not need to wait all the Checkpoint barrier and
will not block some channels. As the Checkpoint barrier is the key mechanism
for Exactly Once guarantee, I am not sure Unaligned Checkpoint could still
achieve Exactly Once guarantee or only AT Least Once?
FLIP-76 :
Unaligned checkpoints will initially be an optional feature. After collecting
experience and implementing all necessary extensions, unaligned checkpoint will
probably be enabled by default for exactly once.
What's more, in the following two configs,
Config 1
env.getCheckpointConfig().enableUnalignedCheckpoints();
Config 2
checkpointCfg.setCheckpointingMode(CheckpointingMode.AT_LEAST_ONCE);
Does Config 2 use a even simpler way for Checkpoint than Unaligned Checkpoint?
Hope for replies!
Weizheng
