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本文主要研究一下flink TaskManager的memory大小设置
flink-conf.yaml
flink-release-1.7.2/flink-dist/src/main/resources/flink-conf.yaml
# The heap size for the TaskManager JVM
taskmanager.heap.size: 1024m
# The number of task slots that each TaskManager offers. Each slot runs one parallel pipeline.
taskmanager.numberOfTaskSlots: 1
# Specify whether TaskManager's managed memory should be allocated when starting
# up (true) or when memory is requested.
#
# We recommend to set this value to 'true' only in setups for pure batch
# processing (DataSet API). Streaming setups currently do not use the TaskManager's
# managed memory: The 'rocksdb' state backend uses RocksDB's own memory management,
# while the 'memory' and 'filesystem' backends explicitly keep data as objects
# to save on serialization cost.
#
# taskmanager.memory.preallocate: false
# The amount of memory going to the network stack. These numbers usually need
# no tuning. Adjusting them may be necessary in case of an "Insufficient number
# of network buffers" error. The default min is 64MB, teh default max is 1GB.
#
# taskmanager.network.memory.fraction: 0.1
# taskmanager.network.memory.min: 64mb
# taskmanager.network.memory.max: 1gb
- flink-conf.yaml提供了taskmanager.heap.size来设置taskmanager的memory(
heap及offHeap)大小 - 提供了taskmanager.memory相关配置(
taskmanager.memory.fraction、taskmanager.memory.off-heap、taskmanager.memory.preallocate、taskmanager.memory.segment-size、taskmanager.memory.size)用于设置memory - 提供了taskmanager.network.memory相关配置(
taskmanager.network.detailed-metrics、taskmanager.network.memory.buffers-per-channel、taskmanager.network.memory.floating-buffers-per-gate、taskmanager.network.memory.fraction、taskmanager.network.memory.max、taskmanager.network.memory.min)用于设置taskmanager的network stack的内存
config.sh
flink-release-1.7.2/flink-dist/src/main/flink-bin/bin/config.sh
#!/usr/bin/env bash
# WARNING !!! , these values are only used if there is nothing else is specified in
# conf/flink-conf.yaml
DEFAULT_ENV_PID_DIR="/tmp" # Directory to store *.pid files to
DEFAULT_ENV_LOG_MAX=5 # Maximum number of old log files to keep
DEFAULT_ENV_JAVA_OPTS="" # Optional JVM args
DEFAULT_ENV_JAVA_OPTS_JM="" # Optional JVM args (JobManager)
DEFAULT_ENV_JAVA_OPTS_TM="" # Optional JVM args (TaskManager)
DEFAULT_ENV_JAVA_OPTS_HS="" # Optional JVM args (HistoryServer)
DEFAULT_ENV_SSH_OPTS="" # Optional SSH parameters running in cluster mode
DEFAULT_YARN_CONF_DIR="" # YARN Configuration Directory, if necessary
DEFAULT_HADOOP_CONF_DIR="" # Hadoop Configuration Directory, if necessary
KEY_TASKM_MEM_SIZE="taskmanager.heap.size"
KEY_TASKM_MEM_MB="taskmanager.heap.mb"
KEY_TASKM_MEM_MANAGED_SIZE="taskmanager.memory.size"
KEY_TASKM_MEM_MANAGED_FRACTION="taskmanager.memory.fraction"
KEY_TASKM_OFFHEAP="taskmanager.memory.off-heap"
KEY_TASKM_MEM_PRE_ALLOCATE="taskmanager.memory.preallocate"
KEY_TASKM_NET_BUF_FRACTION="taskmanager.network.memory.fraction"
KEY_TASKM_NET_BUF_MIN="taskmanager.network.memory.min"
KEY_TASKM_NET_BUF_MAX="taskmanager.network.memory.max"
KEY_TASKM_NET_BUF_NR="taskmanager.network.numberOfBuffers" # fallback
KEY_TASKM_COMPUTE_NUMA="taskmanager.compute.numa"
# Define FLINK_TM_HEAP if it is not already set
if [ -z "${FLINK_TM_HEAP}" ]; then
FLINK_TM_HEAP=$(readFromConfig ${KEY_TASKM_MEM_SIZE} 0 "${YAML_CONF}")
fi
# Try read old config key, if new key not exists
if [ "${FLINK_TM_HEAP}" == 0 ]; then
FLINK_TM_HEAP_MB=$(readFromConfig ${KEY_TASKM_MEM_MB} 0 "${YAML_CONF}")
fi
# Define FLINK_TM_MEM_MANAGED_SIZE if it is not already set
if [ -z "${FLINK_TM_MEM_MANAGED_SIZE}" ]; then
FLINK_TM_MEM_MANAGED_SIZE=$(readFromConfig ${KEY_TASKM_MEM_MANAGED_SIZE} 0 "${YAML_CONF}")
if hasUnit ${FLINK_TM_MEM_MANAGED_SIZE}; then
FLINK_TM_MEM_MANAGED_SIZE=$(getMebiBytes $(parseBytes ${FLINK_TM_MEM_MANAGED_SIZE}))
else
FLINK_TM_MEM_MANAGED_SIZE=$(getMebiBytes $(parseBytes ${FLINK_TM_MEM_MANAGED_SIZE}"m"))
fi
fi
# Define FLINK_TM_MEM_MANAGED_FRACTION if it is not already set
if [ -z "${FLINK_TM_MEM_MANAGED_FRACTION}" ]; then
FLINK_TM_MEM_MANAGED_FRACTION=$(readFromConfig ${KEY_TASKM_MEM_MANAGED_FRACTION} 0.7 "${YAML_CONF}")
fi
# Define FLINK_TM_OFFHEAP if it is not already set
if [ -z "${FLINK_TM_OFFHEAP}" ]; then
FLINK_TM_OFFHEAP=$(readFromConfig ${KEY_TASKM_OFFHEAP} "false" "${YAML_CONF}")
fi
# Define FLINK_TM_MEM_PRE_ALLOCATE if it is not already set
if [ -z "${FLINK_TM_MEM_PRE_ALLOCATE}" ]; then
FLINK_TM_MEM_PRE_ALLOCATE=$(readFromConfig ${KEY_TASKM_MEM_PRE_ALLOCATE} "false" "${YAML_CONF}")
fi
# Define FLINK_TM_NET_BUF_FRACTION if it is not already set
if [ -z "${FLINK_TM_NET_BUF_FRACTION}" ]; then
FLINK_TM_NET_BUF_FRACTION=$(readFromConfig ${KEY_TASKM_NET_BUF_FRACTION} 0.1 "${YAML_CONF}")
fi
# Define FLINK_TM_NET_BUF_MIN and FLINK_TM_NET_BUF_MAX if not already set (as a fallback)
if [ -z "${FLINK_TM_NET_BUF_MIN}" -a -z "${FLINK_TM_NET_BUF_MAX}" ]; then
FLINK_TM_NET_BUF_MIN=$(readFromConfig ${KEY_TASKM_NET_BUF_NR} -1 "${YAML_CONF}")
if [ $FLINK_TM_NET_BUF_MIN != -1 ]; then
FLINK_TM_NET_BUF_MIN=$(parseBytes ${FLINK_TM_NET_BUF_MIN})
FLINK_TM_NET_BUF_MAX=${FLINK_TM_NET_BUF_MIN}
fi
fi
# Define FLINK_TM_NET_BUF_MIN if it is not already set
if [ -z "${FLINK_TM_NET_BUF_MIN}" -o "${FLINK_TM_NET_BUF_MIN}" = "-1" ]; then
# default: 64MB = 67108864 bytes (same as the previous default with 2048 buffers of 32k each)
FLINK_TM_NET_BUF_MIN=$(readFromConfig ${KEY_TASKM_NET_BUF_MIN} 67108864 "${YAML_CONF}")
FLINK_TM_NET_BUF_MIN=$(parseBytes ${FLINK_TM_NET_BUF_MIN})
fi
# Define FLINK_TM_NET_BUF_MAX if it is not already set
if [ -z "${FLINK_TM_NET_BUF_MAX}" -o "${FLINK_TM_NET_BUF_MAX}" = "-1" ]; then
# default: 1GB = 1073741824 bytes
FLINK_TM_NET_BUF_MAX=$(readFromConfig ${KEY_TASKM_NET_BUF_MAX} 1073741824 "${YAML_CONF}")
FLINK_TM_NET_BUF_MAX=$(parseBytes ${FLINK_TM_NET_BUF_MAX})
fi
- config.sh在相关变量没有设置的前提下，初始化了FLINK_TM_HEAP、FLINK_TM_MEM_MANAGED_SIZE、FLINK_TM_MEM_MANAGED_FRACTION、FLINK_TM_OFFHEAP、FLINK_TM_MEM_PRE_ALLOCATE、FLINK_TM_NET_BUF_FRACTION等变量
taskmanager.sh
flink-release-1.7.2/flink-dist/src/main/flink-bin/bin/taskmanager.sh
#!/usr/bin/env bash
# Start/stop a Flink TaskManager.
USAGE="Usage: taskmanager.sh (start|start-foreground|stop|stop-all)"
STARTSTOP=$1
ARGS=("${@:2}")
if [[ $STARTSTOP != "start" ]] && [[ $STARTSTOP != "start-foreground" ]] && [[ $STARTSTOP != "stop" ]] && [[ $STARTSTOP != "stop-all" ]]; then
echo $USAGE
exit 1
fi
bin=`dirname "$0"`
bin=`cd "$bin"; pwd`
. "$bin"/config.sh
ENTRYPOINT=taskexecutor
if [[ $STARTSTOP == "start" ]] || [[ $STARTSTOP == "start-foreground" ]]; then
# if memory allocation mode is lazy and no other JVM options are set,
# set the 'Concurrent Mark Sweep GC'
if [[ $FLINK_TM_MEM_PRE_ALLOCATE == "false" ]] && [ -z "${FLINK_ENV_JAVA_OPTS}" ] && [ -z "${FLINK_ENV_JAVA_OPTS_TM}" ]; then
export JVM_ARGS="$JVM_ARGS -XX:+UseG1GC"
fi
if [ ! -z "${FLINK_TM_HEAP_MB}" ] && [ "${FLINK_TM_HEAP}" == 0 ]; then
echo "used deprecated key \`${KEY_TASKM_MEM_MB}\`, please replace with key \`${KEY_TASKM_MEM_SIZE}\`"
else
flink_tm_heap_bytes=$(parseBytes ${FLINK_TM_HEAP})
FLINK_TM_HEAP_MB=$(getMebiBytes ${flink_tm_heap_bytes})
fi
if [[ ! ${FLINK_TM_HEAP_MB} =~ ${IS_NUMBER} ]] || [[ "${FLINK_TM_HEAP_MB}" -lt "0" ]]; then
echo "[ERROR] Configured TaskManager JVM heap size is not a number. Please set '${KEY_TASKM_MEM_SIZE}' in ${FLINK_CONF_FILE}."
exit 1
fi
if [ "${FLINK_TM_HEAP_MB}" -gt "0" ]; then
TM_HEAP_SIZE=$(calculateTaskManagerHeapSizeMB)
# Long.MAX_VALUE in TB: This is an upper bound, much less direct memory will be used
TM_MAX_OFFHEAP_SIZE="8388607T"
export JVM_ARGS="${JVM_ARGS} -Xms${TM_HEAP_SIZE}M -Xmx${TM_HEAP_SIZE}M -XX:MaxDirectMemorySize=${TM_MAX_OFFHEAP_SIZE}"
fi
# Add TaskManager-specific JVM options
export FLINK_ENV_JAVA_OPTS="${FLINK_ENV_JAVA_OPTS} ${FLINK_ENV_JAVA_OPTS_TM}"
# Startup parameters
ARGS+=("--configDir" "${FLINK_CONF_DIR}")
fi
if [[ $STARTSTOP == "start-foreground" ]]; then
exec "${FLINK_BIN_DIR}"/flink-console.sh $ENTRYPOINT "${ARGS[@]}"
else
if [[ $FLINK_TM_COMPUTE_NUMA == "false" ]]; then
# Start a single TaskManager
"${FLINK_BIN_DIR}"/flink-daemon.sh $STARTSTOP $ENTRYPOINT "${ARGS[@]}"
else
# Example output from `numactl --show` on an AWS c4.8xlarge:
# policy: default
# preferred node: current
# physcpubind: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35
# cpubind: 0 1
# nodebind: 0 1
# membind: 0 1
read -ra NODE_LIST <<< $(numactl --show | grep "^nodebind: ")
for NODE_ID in "${NODE_LIST[@]:1}"; do
# Start a TaskManager for each NUMA node
numactl --membind=$NODE_ID --cpunodebind=$NODE_ID -- "${FLINK_BIN_DIR}"/flink-daemon.sh $STARTSTOP $ENTRYPOINT "${ARGS[@]}"
done
fi
fi
- taskmanager.sh首先调用config.sh初始化相关变量，之后计算并export了JVM_ARGS及FLINK_ENV_JAVA_OPTS，最后调用flink-console.sh启动相关类
- 如果FLINK_TM_MEM_PRE_ALLOCATE为false且FLINK_ENV_JAVA_OPTS及FLINK_ENV_JAVA_OPTS_TM都没有设置，则追加-XX:+UseG1GC到JVM_ARGS；之后读取FLINK_TM_HEAP到FLINK_TM_HEAP_MB；如果FLINK_TM_HEAP_MB大于0则通过calculateTaskManagerHeapSizeMB计算TM_HEAP_SIZE，然后以TM_HEAP_SIZE设置xms及Xmx，以TM_MAX_OFFHEAP_SIZE设置MaxDirectMemorySize，追加到JVM_ARGS中；而FLINK_ENV_JAVA_OPTS_TM则会追加到FLINK_ENV_JAVA_OPTS
- calculateTaskManagerHeapSizeMB在config.sh中有定义，另外其对应的java代码在TaskManagerServices.calculateHeapSizeMB
TaskManagerServices
flink-runtime_2.11-1.7.2-sources.jar!/org/apache/flink/runtime/taskexecutor/TaskManagerServices.java
public class TaskManagerServices {
//......
/**
* Calculates the amount of heap memory to use (to set via <tt>-Xmx</tt> and <tt>-Xms</tt>)
* based on the total memory to use and the given configuration parameters.
*
* @param totalJavaMemorySizeMB
* overall available memory to use (heap and off-heap)
* @param config
* configuration object
*
* @return heap memory to use (in megabytes)
*/
public static long calculateHeapSizeMB(long totalJavaMemorySizeMB, Configuration config) {
Preconditions.checkArgument(totalJavaMemorySizeMB > 0);
// subtract the Java memory used for network buffers (always off-heap)
final long networkBufMB =
calculateNetworkBufferMemory(
totalJavaMemorySizeMB << 20, // megabytes to bytes
config) >> 20; // bytes to megabytes
final long remainingJavaMemorySizeMB = totalJavaMemorySizeMB - networkBufMB;
// split the available Java memory between heap and off-heap
final boolean useOffHeap = config.getBoolean(TaskManagerOptions.MEMORY_OFF_HEAP);
final long heapSizeMB;
if (useOffHeap) {
long offHeapSize;
String managedMemorySizeDefaultVal = TaskManagerOptions.MANAGED_MEMORY_SIZE.defaultValue();
if (!config.getString(TaskManagerOptions.MANAGED_MEMORY_SIZE).equals(managedMemorySizeDefaultVal)) {
try {
offHeapSize = MemorySize.parse(config.getString(TaskManagerOptions.MANAGED_MEMORY_SIZE), MEGA_BYTES).getMebiBytes();
} catch (IllegalArgumentException e) {
throw new IllegalConfigurationException(
"Could not read " + TaskManagerOptions.MANAGED_MEMORY_SIZE.key(), e);
}
} else {
offHeapSize = Long.valueOf(managedMemorySizeDefaultVal);
}
if (offHeapSize <= 0) {
// calculate off-heap section via fraction
double fraction = config.getFloat(TaskManagerOptions.MANAGED_MEMORY_FRACTION);
offHeapSize = (long) (fraction * remainingJavaMemorySizeMB);
}
TaskManagerServicesConfiguration
.checkConfigParameter(offHeapSize < remainingJavaMemorySizeMB, offHeapSize,
TaskManagerOptions.MANAGED_MEMORY_SIZE.key(),
"Managed memory size too large for " + networkBufMB +
" MB network buffer memory and a total of " + totalJavaMemorySizeMB +
" MB JVM memory");
heapSizeMB = remainingJavaMemorySizeMB - offHeapSize;
} else {
heapSizeMB = remainingJavaMemorySizeMB;
}
return heapSizeMB;
}
/**
* Calculates the amount of memory used for network buffers based on the total memory to use and
* the according configuration parameters.
*
* <p>The following configuration parameters are involved:
* <ul>
* <li>{@link TaskManagerOptions#NETWORK_BUFFERS_MEMORY_FRACTION},</li>
* <li>{@link TaskManagerOptions#NETWORK_BUFFERS_MEMORY_MIN},</li>
* <li>{@link TaskManagerOptions#NETWORK_BUFFERS_MEMORY_MAX}, and</li>
* <li>{@link TaskManagerOptions#NETWORK_NUM_BUFFERS} (fallback if the ones above do not exist)</li>
* </ul>.
*
* @param totalJavaMemorySize
* overall available memory to use (heap and off-heap, in bytes)
* @param config
* configuration object
*
* @return memory to use for network buffers (in bytes); at least one memory segment
*/
@SuppressWarnings("deprecation")
public static long calculateNetworkBufferMemory(long totalJavaMemorySize, Configuration config) {
Preconditions.checkArgument(totalJavaMemorySize > 0);
int segmentSize =
checkedDownCast(MemorySize.parse(config.getString(TaskManagerOptions.MEMORY_SEGMENT_SIZE)).getBytes());
final long networkBufBytes;
if (TaskManagerServicesConfiguration.hasNewNetworkBufConf(config)) {
// new configuration based on fractions of available memory with selectable min and max
float networkBufFraction = config.getFloat(TaskManagerOptions.NETWORK_BUFFERS_MEMORY_FRACTION);
long networkBufMin = MemorySize.parse(config.getString(TaskManagerOptions.NETWORK_BUFFERS_MEMORY_MIN)).getBytes();
long networkBufMax = MemorySize.parse(config.getString(TaskManagerOptions.NETWORK_BUFFERS_MEMORY_MAX)).getBytes();
TaskManagerServicesConfiguration
.checkNetworkBufferConfig(segmentSize, networkBufFraction, networkBufMin, networkBufMax);
networkBufBytes = Math.min(networkBufMax, Math.max(networkBufMin,
(long) (networkBufFraction * totalJavaMemorySize)));
TaskManagerServicesConfiguration
.checkConfigParameter(networkBufBytes < totalJavaMemorySize,
"(" + networkBufFraction + ", " + networkBufMin + ", " + networkBufMax + ")",
"(" + TaskManagerOptions.NETWORK_BUFFERS_MEMORY_FRACTION.key() + ", " +
TaskManagerOptions.NETWORK_BUFFERS_MEMORY_MIN.key() + ", " +
TaskManagerOptions.NETWORK_BUFFERS_MEMORY_MAX.key() + ")",
"Network buffer memory size too large: " + networkBufBytes + " >= " +
totalJavaMemorySize + " (total JVM memory size)");
TaskManagerServicesConfiguration
.checkConfigParameter(networkBufBytes >= segmentSize,
"(" + networkBufFraction + ", " + networkBufMin + ", " + networkBufMax + ")",
"(" + TaskManagerOptions.NETWORK_BUFFERS_MEMORY_FRACTION.key() + ", " +
TaskManagerOptions.NETWORK_BUFFERS_MEMORY_MIN.key() + ", " +
TaskManagerOptions.NETWORK_BUFFERS_MEMORY_MAX.key() + ")",
"Network buffer memory size too small: " + networkBufBytes + " < " +
segmentSize + " (" + TaskManagerOptions.MEMORY_SEGMENT_SIZE.key() + ")");
} else {
// use old (deprecated) network buffers parameter
int numNetworkBuffers = config.getInteger(TaskManagerOptions.NETWORK_NUM_BUFFERS);
networkBufBytes = (long) numNetworkBuffers * (long) segmentSize;
TaskManagerServicesConfiguration.checkNetworkConfigOld(numNetworkBuffers);
TaskManagerServicesConfiguration
.checkConfigParameter(networkBufBytes < totalJavaMemorySize,
networkBufBytes, TaskManagerOptions.NETWORK_NUM_BUFFERS.key(),
"Network buffer memory size too large: " + networkBufBytes + " >= " +
totalJavaMemorySize + " (total JVM memory size)");
TaskManagerServicesConfiguration
.checkConfigParameter(networkBufBytes >= segmentSize,
networkBufBytes, TaskManagerOptions.NETWORK_NUM_BUFFERS.key(),
"Network buffer memory size too small: " + networkBufBytes + " < " +
segmentSize + " (" + TaskManagerOptions.MEMORY_SEGMENT_SIZE.key() + ")");
}
return networkBufBytes;
}
//......
}
- FLINK_TM_HEAP设置的是taskmanager的memory(
heap及offHeap)大小，而network buffers总是使用offHeap，因而这里首先要从FLINK_TM_HEAP扣减掉这部分offHeap然后重新计算Xms及Xmx - calculateHeapSizeMB先调用calculateNetworkBufferMemory计算networkBufMB，然后从totalJavaMemorySizeMB扣减掉networkBufMB得到remainingJavaMemorySizeMB
- 之后读取taskmanager.memory.off-heap设置，默认为false，则直接以remainingJavaMemorySizeMB返回；如果为true，则需要计算offHeapSize的值，然后从remainingJavaMemorySizeMB扣减offHeapSize再返回
小结
- flink-conf.yaml提供了taskmanager.heap.size来设置taskmanager的memory(
heap及offHeap)大小；提供了taskmanager.memory相关配置(taskmanager.memory.fraction、taskmanager.memory.off-heap、taskmanager.memory.preallocate、taskmanager.memory.segment-size、taskmanager.memory.size)用于设置memory；提供了taskmanager.network.memory相关配置(taskmanager.network.detailed-metrics、taskmanager.network.memory.buffers-per-channel、taskmanager.network.memory.floating-buffers-per-gate、taskmanager.network.memory.fraction、taskmanager.network.memory.max、taskmanager.network.memory.min)用于设置taskmanager的network stack的内存 - taskmanager.sh首先调用config.sh初始化相关变量，之后计算并export了JVM_ARGS及FLINK_ENV_JAVA_OPTS，最后调用flink-console.sh启动相关类；如果FLINK_TM_MEM_PRE_ALLOCATE为false且FLINK_ENV_JAVA_OPTS及FLINK_ENV_JAVA_OPTS_TM都没有设置，则追加-XX:+UseG1GC到JVM_ARGS；之后读取FLINK_TM_HEAP到FLINK_TM_HEAP_MB；如果FLINK_TM_HEAP_MB大于0则通过calculateTaskManagerHeapSizeMB计算TM_HEAP_SIZE，然后以TM_HEAP_SIZE设置xms及Xmx，以TM_MAX_OFFHEAP_SIZE设置MaxDirectMemorySize，追加到JVM_ARGS中；而FLINK_ENV_JAVA_OPTS_TM则会追加到FLINK_ENV_JAVA_OPTS；calculateTaskManagerHeapSizeMB在config.sh中有定义，另外其对应的java代码在TaskManagerServices.calculateHeapSizeMB
- FLINK_TM_HEAP设置的是taskmanager的memory(
heap及offHeap)大小，而network buffers总是使用offHeap，因而这里首先要从FLINK_TM_HEAP扣减掉这部分offHeap然后重新计算Xms及Xmx；calculateHeapSizeMB先调用calculateNetworkBufferMemory计算networkBufMB，然后从totalJavaMemorySizeMB扣减掉networkBufMB得到remainingJavaMemorySizeMB；之后读取taskmanager.memory.off-heap设置，默认为false，则直接以remainingJavaMemorySizeMB返回；如果为true，则需要计算offHeapSize的值，然后从remainingJavaMemorySizeMB扣减offHeapSize再返回
由此可见最后的jvm参数取决于JVM_ARGS及FLINK_ENV_JAVA_OPTS；其中注意不要设置内存相关参数到JVM_ARGS，因为taskmanager.sh在FLINK_TM_HEAP_MB大于0的时候，则使用该值计算TM_HEAP_SIZE设置Xms及Xmx追加到JVM_ARGS变量中，而FLINK_TM_HEAP_MB则取决于FLINK_TM_HEAP或者taskmanager.heap.size配置；FLINK_ENV_JAVA_OPTS的配置则取决于env.java.opts以及env.java.opts.taskmanager；因而要配置taskmanager的memory(
heap及offHeap)大小，可以指定FLINK_TM_HEAP环境变量(比如FLINK_TM_HEAP=512m)，或者在flink-conf.yaml中指定taskmanager.heap.size；而最终的Xms及Xmx则是FLINK_TM_HEAP扣减掉offHeap而来，确定使用offHeap为network buffers，其余的看是否开启taskmanager.memory.off-heap，默认为false
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