范例：
StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();
// start a checkpoint every 1000 ms
env.enableCheckpointing(1000);
// advanced options:
// set mode to exactly-once (this is the default)
env.getCheckpointConfig().setCheckpointingMode(CheckpointingMode.EXACTLY_ONCE);
// checkpoints have to complete within one minute, or are discarded
env.getCheckpointConfig().setCheckpointTimeout(60000);
// make sure 500 ms of progress happen between checkpoints
env.getCheckpointConfig().setMinPauseBetweenCheckpoints(500);
// allow only one checkpoint to be in progress at the same time
env.getCheckpointConfig().setMaxConcurrentCheckpoints(1);
// enable externalized checkpoints which are retained after job cancellation
env.getCheckpointConfig().enableExternalizedCheckpoints(ExternalizedCheckpointCleanup.RETAIN_ON_CANCELLATION);
// This determines if a task will be failed if an error occurs in the execution of the task’s checkpoint procedure.
env.getCheckpointConfig().setFailOnCheckpointingErrors(true);
使用
StreamExecutionEnvironment.enableCheckpointing方法來設置開啟checkpoint
（具體可以使用StreamExecutionEnvironment.getCheckpointConfig.enableCheckpointing(long interval)），
或者StreamExecutionEnvironment.getCheckpointConfig.enableCheckpointing(long interval, CheckpointingMode mode)。
interval用于指定checkpoint的觸發間隔(單位milliseconds)
而CheckpointingMode默認是CheckpointingMode.EXACTLY_ONCE
也可以指定為CheckpointingMode.AT_LEAST_ONCE也可以通過
StreamExecutionEnvironment.getCheckpointConfig().setCheckpointingMode來設置CheckpointingMode，
一般對于超低延遲的應用(大概幾毫秒)可以使用CheckpointingMode.AT_LEAST_ONCE，其他大部分應用使用CheckpointingMode.EXACTLY_ONCE就可以
checkpointTimeout用于指定checkpoint執行的超時時間(單位milliseconds)，超時沒完成就會被abort掉。minPauseBetweenCheckpoints用于指定checkpoint距上一個checkpoint完成之后最少等多久可以出發另一個checkpoint，
當指定這個參數時，maxConcurrentCheckpoints的值為1maxConcurrentCheckpoints用于指定運行中的checkpoint最多可以有多少個；
如果有設置了minPauseBetweenCheckpoints，則maxConcurrentCheckpoints這個參數就不起作用了(大于1的值不起作用)enableExternalizedCheckpoints用于開啟checkpoints的外部持久化，但是在job失敗的時候不會自動清理，需要自己手工清理state；ExternalizedCheckpointCleanup用于指定當job canceled的時候externalized checkpoint該如何清理，DELETE_ON_CANCELLATION的話，在job canceled的時候會自動刪除externalized state，但是如果是FAILED的狀態則會保留；RETAIN_ON_CANCELLATION則在job canceled的時候會保留externalized checkpoint statefailOnCheckpointingErrors用于指定在checkpoint發生異常的時候，是否應該fail該task，默認為true，如果設置為false，則task會拒絕checkpoint然后繼續運行
flink-conf.yaml相關配置：
#==============================================================================
# Fault tolerance and checkpointing
#==============================================================================
# The backend that will be used to store operator state checkpoints if
# checkpointing is enabled.
#
# Supported backends are 'jobmanager', 'filesystem', 'rocksdb', or the
# <class-name-of-factory>.
#
# state.backend: filesystem
# Directory for checkpoints filesystem, when using any of the default bundled
# state backends.
#
# state.checkpoints.dir: hdfs://namenode-host:port/flink-checkpoints
# Default target directory for savepoints, optional.
#
# state.savepoints.dir: hdfs://namenode-host:port/flink-checkpoints
# Flag to enable/disable incremental checkpoints for backends that
# support incremental checkpoints (like the RocksDB state backend).
#
# state.backend.incremental: false
-
state.backend用于指定checkpoint state存儲的backend，默認為none -
state.backend.async用于指定backend是否使用異步snapshot(默認為true)，有些不支持async或者只支持async的state backend可能會忽略這個參數 -
state.backend.fs.memory-threshold，默認為1024，用于指定存儲于files的state大小閾[yù]值，如果小于該值則會存儲在root checkpoint metadata file -
state.backend.incremental，默認為false，用于指定是否采用增量checkpoint，有些不支持增量checkpoint的backend會忽略該配置 -
state.backend.local-recovery，默認為false -
state.checkpoints.dir，默認為none，用于指定checkpoint的data files和meta data存儲的目錄，該目錄必須對所有參與的TaskManagers及JobManagers可見 -
state.checkpoints.num-retained，默認為1，用于指定保留的已完成的checkpoints個數 -
state.savepoints.dir，默認為none，用于指定savepoints的默認目錄 -
taskmanager.state.local.root-dirs，默認為none
小結：
可以通過使用
StreamExecutionEnvironment.enableCheckpointing方法來設置開啟checkpoint；具體可以使用enableCheckpointing(long interval)，或者enableCheckpointing(long interval, CheckpointingMode mode)checkpoint的高級配置可以配置enableExternalizedCheckpoints(用于開啟checkpoints的外部持久化，在job failed的時候externalized checkpoint state無法自動清理，但是在job canceled的時候可以配置是刪除還是保留state)在
flink-conf.yaml里頭也有checkpoint的相關配置，主要是state backend的配置，比如state.backend.async、state.backend.incremental、state.checkpoints.dir、state.savepoints.dir等
Java 配置實例：
/**
* 是否重啟標識flag
*/
private static boolean replayFlag = true;
/**
* 重啟次數
*/
private static Integer replayTimes;
/**
* 重啟時間間隔
*/
private static Integer replaySeconds;
private static Long checkPointTime;
StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();
if (replayFlag) {
env.setRestartStrategy(RestartStrategies.fixedDelayRestart(
replayTimes,
Time.of(replaySeconds, TimeUnit.SECONDS)
));
CheckpointConfig config = env.getCheckpointConfig();
//env.setStateBackend(new FsStateBackend(checkPointDir));
// 任務流取消和故障時會保留Checkpoint數據，以便根據實際需要恢復到指定的Checkpoint
config.enableExternalizedCheckpoints(CheckpointConfig.ExternalizedCheckpointCleanup.RETAIN_ON_CANCELLATION);
// 設置checkpoint的周期, 每隔1000 ms進行啟動一個檢查點
config.setCheckpointInterval(checkPointTime);
// 設置模式為exactly-once
config.setCheckpointingMode(CheckpointingMode.EXACTLY_ONCE);
// 確保檢查點之間有至少500 ms的間隔【checkpoint最小間隔】
config.setMinPauseBetweenCheckpoints(500);
// 檢查點必須在一分鐘內完成，或者被丟棄【checkpoint的超時時間】
config.setCheckpointTimeout(checkPointTime);
// 同一時間只允許進行一個檢查點
config.setMaxConcurrentCheckpoints(1);
}
