[flink] branch master updated: [FLINK-25640][docs] Enhance the document for blocking shuffle

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     new 5a854a3  [FLINK-25640][docs] Enhance the document for blocking shuffle
5a854a3 is described below

commit 5a854a31aab7daa5f0240d1cc05cc102d2ff4574
Author: kevin.cyj <ke...@alibaba-inc.com>
AuthorDate: Fri Feb 11 10:50:07 2022 +0800

    [FLINK-25640][docs] Enhance the document for blocking shuffle
    
    This closes #18723.
---
 docs/content.zh/docs/ops/batch/blocking_shuffle.md | 51 ++++++++++++++++------
 docs/content/docs/ops/batch/blocking_shuffle.md    | 48 +++++++++++++++-----
 2 files changed, 74 insertions(+), 25 deletions(-)

diff --git a/docs/content.zh/docs/ops/batch/blocking_shuffle.md b/docs/content.zh/docs/ops/batch/blocking_shuffle.md
index da1384c..b2b38b9 100644
--- a/docs/content.zh/docs/ops/batch/blocking_shuffle.md
+++ b/docs/content.zh/docs/ops/batch/blocking_shuffle.md
@@ -29,7 +29,7 @@ under the License.
 
 ## 总览
 
-Flink [DataStream API]({{< ref "docs/dev/datastream/execution_mode" >}}) 和 [Table / SQL]({{< ref "/docs/dev/table/overview" >}}) 都支持通过批处理执行模式处理有界输入。此模式是通过 blocking shuffle 进行网络传输。与流式应用使用管道 shuffle 阻塞交换的数据并存储，然后下游任务通过网络获取这些值的方式不同。这种交换减少了执行作业所需的资源，因为它不需要同时运行上游和下游任务。 
+Flink [DataStream API]({{< ref "docs/dev/datastream/execution_mode" >}}) 和 [Table / SQL]({{< ref "/docs/dev/table/overview" >}}) 都支持通过批处理执行模式处理有界输入。此模式是通过 blocking shuffle 进行网络传输。与流式应用使用管道 shuffle 阻塞交换的数据并存储，然后下游任务通过网络获取这些值的方式不同。这种交换减少了执行作业所需的资源，因为它不需要同时运行上游和下游任务。
 
 总的来说，Flink 提供了两种不同类型的 blocking shuffles：`Hash shuffle` 和 `Sort shuffle`。
 
@@ -43,7 +43,7 @@ Flink [DataStream API]({{< ref "docs/dev/datastream/execution_mode" >}}) 和 [Ta
 
 - `file`: 通过标准文件 IO 写文件，读取和传输文件需要通过 Netty 的 `FileRegion`。`FileRegion` 依靠系统调用 `sendfile` 来减少数据拷贝和内存消耗。
 - `mmap`: 通过系统调用 `mmap` 来读写文件。
-- `Auto`: 通过标准文件 IO 写文件，对于文件读取，在 32 位机器上降级到 `file` 选项并且在 64 位机器上使用 `mmap` 。这是为了避免在 32 位机器上 java 实现 `mmap` 的文件大小限制。
+- `auto`: 通过标准文件 IO 写文件，对于文件读取，在 32 位机器上降级到 `file` 选项并且在 64 位机器上使用 `mmap` 。这是为了避免在 32 位机器上 java 实现 `mmap` 的文件大小限制。
 
 可通过设置 [TaskManager 参数]({{< ref "docs/deployment/config#taskmanager-network-blocking-shuffle-type" >}}) 选择不同的机制。
 
@@ -56,11 +56,9 @@ Flink [DataStream API]({{< ref "docs/dev/datastream/execution_mode" >}}) 和 [Ta
 {{< /hint >}}
 
 {{< hint info >}}
-`mmap`使用的内存不计算进已有配置的内存限制中，但是一些资源管理框架比如 yarn 将追踪这块内存使用，并且如果容器使用内存超过阈值会被杀掉。
+`mmap`使用的内存不计算进已有配置的内存限制中，但是一些资源管理框架比如 YARN 将追踪这块内存使用，并且如果容器使用内存超过阈值会被杀掉。
 {{< /hint >}}
 
-为了进一步的提升性能，对于绝大多数的任务我们推荐 [启用压缩]({{< ref "docs/deployment/config">}}#taskmanager-network-blocking-shuffle-compression-enabled) ，除非数据很难被压缩。
-
 `Hash Shuffle` 在小规模运行在固态硬盘的任务情况下效果显著，但是依旧有一些问题:
 
 1. 如果任务的规模庞大将会创建很多文件，并且要求同时对这些文件进行大量的写操作。
@@ -68,16 +66,14 @@ Flink [DataStream API]({{< ref "docs/dev/datastream/execution_mode" >}}) 和 [Ta
 
 ## Sort Shuffle
 
-`Sort Shuffle` 是 1.13 版中引入的另一种 blocking shuffle 实现，它在 1.15 版本成为默认。不同于 `Hash Shuffle`，sort shuffle 将每个分区结果写入到一个文件。当多个下游任务同时读取结果分片，数据文件只会被打开一次并共享给所有的读请求。因此，集群使用更少的资源。例如：节点和文件描述符以提升稳定性。此外，通过写更少的文件和尽可能线性的读取文件，尤其是在使用机械硬盘情况下 sort shuffle 可以获得比 hash shuffle 更好的性能。另外，`sort shuffle` 使用额外管理的内存作为读数据缓存并不依赖 `sendfile` 或 `mmap` 机制，因此也适用于 [SSL]({{< ref "docs/deployment/security/security-ssl" >}})。关于 sort shuffle 的更多细节请参考 [FLINK-19582](https://issues.apache.org/jira/browse/FLINK-19582) 和 [FLINK-19614](h [...]
+`Sort Shuffle` 是 1.13 版中引入的另一种 blocking shuffle 实现，它在 1.15 版本成为默认。不同于 `Hash Shuffle`，`Sort Shuffle` 将每个分区结果写入到一个文件。当多个下游任务同时读取结果分片，数据文件只会被打开一次并共享给所有的读请求。因此，集群使用更少的资源。例如：节点和文件描述符以提升稳定性。此外，通过写更少的文件和尽可能线性的读取文件，尤其是在使用机械硬盘情况下 `Sort Shuffle` 可以获得比 `Hash Shuffle` 更好的性能。另外，`Sort Shuffle` 使用额外管理的内存作为读数据缓存并不依赖 `sendfile` 或 `mmap` 机制，因此也适用于 [SSL]({{< ref "docs/deployment/security/security-ssl" >}})。关于 `Sort Shuffle` 的更多细节请参考 [FLINK-19582](https://issues.apache.org/jira/browse/FLINK-19582) 和 [FLINK- [...]
 
 当使用sort blocking shuffle的时候有些配置需要适配:
-- [taskmanager.network.blocking-shuffle.compression.enabled]({{< ref "docs/deployment/config" >}}#taskmanager-network-blocking-shuffle-compression-enabled): 配置该选项以启用 shuffle data 压缩，大部分任务建议开启除非你的数据压缩比率比较低。对于 1.14 以及更低的版本默认为 false，1.15 版本起默认为 true。
-- [taskmanager.network.sort-shuffle.min-parallelism]({{< ref "docs/deployment/config" >}}#taskmanager-network-sort-shuffle-min-parallelism): 根据下游任务的并行度配置该选项以启用 sort shuffle。如果并行度低于设置的值，则使用 `hash shuffle`，否则 `sort shuffle`。对于 1.15 以下的版本，它的默认值是 `Integer.MAX_VALUE`，所以默认情况下总是会使用 `hash shuffle`。从 1.15 开始，它的默认值是 1, 所以默认情况下总是会使用 `sort shuffle`。
-- [taskmanager.network.sort-shuffle.min-buffers]({{< ref "docs/deployment/config" >}}#taskmanager-network-sort-shuffle-min-buffers): 配置该选项以控制数据写缓存大小。对于大规模的任务而言，你可能需要调大这个值，正常几百兆内存就足够了。
-- [taskmanager.memory.framework.off-heap.batch-shuffle.size]({{< ref "docs/deployment/config" >}}#taskmanager-memory-framework-off-heap-batch-shuffle-size): 配置该选项以控制数据读取缓存大小。对于大规模的任务而言，你可能需要调大这个值，正常几百兆内存就足够了。
+- [taskmanager.network.sort-shuffle.min-buffers]({{< ref "docs/deployment/config" >}}#taskmanager-network-sort-shuffle-min-buffers): 配置该选项以控制数据写缓存大小。对于大规模的任务而言，你可能需要调大这个值，正常几百兆内存就足够了。因为这部分内存是从网络内存分配的，所以想要增大这个配置值，你可能还需要通过调整 [taskmanager.memory.network.fraction]({{< ref "docs/deployment/config" >}}#taskmanager-memory-network-fraction)，[taskmanager.memory.network.min]({{< ref "docs/deployment/config" >}}#taskmanager-memory-network-min) 和 [taskmanager.memory.network.max]({{< ref "docs/deploy [...]
+- [taskmanager.memory.framework.off-heap.batch-shuffle.size]({{< ref "docs/deployment/config" >}}#taskmanager-memory-framework-off-heap-batch-shuffle-size): 配置该选项以控制数据读取缓存大小。对于大规模的任务而言，你可能需要调大这个值，正常几百兆内存就足够了。因为这部分内存是从框架堆外内存中切分出来的，所以想要增大这个配置值，你还需要通过调整 [taskmanager.memory.framework.off-heap.size]({{< ref "docs/deployment/config" >}}#taskmanager-memory-framework-off-heap-size) 来增大框架堆外内存以避免出现直接内存溢出的错误。
 
 {{< hint info >}}
-目前 `sort shuffle` 只通过分区索引来排序而不是记录本身，也就是说 `sort` 只是被当成数据聚类算法使用。
+目前 `Sort Shuffle` 只通过分区索引来排序而不是记录本身，也就是说 `sort` 只是被当成数据聚类算法使用。
 {{< /hint >}}
 
 ## 如何选择 Blocking Shuffle
@@ -85,5 +81,34 @@ Flink [DataStream API]({{< ref "docs/dev/datastream/execution_mode" >}}) 和 [Ta
 总的来说，
 
 - 对于在固态硬盘上运行的小规模任务而言，两者都可以。
-- 对于在机械硬盘上运行的大规模任务而言，`sort shuffle` 更为合适。
-- 在这两种情况下，你可以考虑 [enabling compression]({{< ref "docs/deployment/config">}}#taskmanager-network-blocking-shuffle-compression-enabled) 来提升性能，除非数据很难被压缩。
+- 对于在机械硬盘上运行的大规模任务而言，`Sort Shuffle` 更为合适。
+
+要在 `Sort Shuffle` 和 `Hash Shuffle` 间切换，你需要配置这个参数：[taskmanager.network.sort-shuffle.min-parallelism]({{< ref "docs/deployment/config" >}}#taskmanager-network-sort-shuffle-min-parallelism)。这个参数根据消费者Task的并发选择当前Task使用`Hash Shuffle` 或 `Sort Shuffle`，如果并发小于配置值则使用 `Hash Shuffle`，否则使用 `Sort Shuffle`。对于 1.15 以下版本，它的默认值是 `Integer.MAX_VALUE`，这意味着 `Hash Shuffle` 是默认实现。从 1.15 起，它的默认值是 1，这意味着 `Sort Shuffle` 是默认实现。
+
+## 性能调优
+
+下面这些建议可以帮助你实现更好的性能，这些对于大规模批作业尤其重要：
+
+1. 如果你使用机械硬盘作为存储设备，请总是使用 `Sort Shuffle`，因为这可以极大的提升稳定性和性能。从 1.15 开始，`Sort Shuffle` 已经成为默认实现，对于 1.14 以及更低版本，你需要通过将 [taskmanager.network.sort-shuffle.min-parallelism]({{< ref "docs/deployment/config" >}}#taskmanager-network-sort-shuffle-min-parallelism) 配置为 1 以手动开启 `Sort Shuffle`。
+2. 对于 `Sort Shuffle` 和 `Hash Shuffle` 两种实现，你都可以考虑开启 [数据压缩]({{< ref "docs/deployment/config">}}#taskmanager-network-blocking-shuffle-compression-enabled) 除非数据本身无法压缩。从 1.15 开启，数据压缩是默认开启的，对于 1.14 以及更低版本你需要手动开启。
+3. 当使用 `Sort Shuffle` 时，减少 [独占网络缓冲区]({{< ref "docs/deployment/config" >}}#taskmanager-network-memory-buffers-per-channel) 并增加 [流动网络缓冲区]({{< ref "docs/deployment/config" >}}#taskmanager-network-memory-floating-buffers-per-gate) 有利于性能提升。对于 1.14 以及更高版本，建议将 [taskmanager.network.memory.buffers-per-channel]({{< ref "docs/deployment/config" >}}#taskmanager-network-memory-buffers-per-channel) 设为 0 并且将 [taskmanager.network.memory.floating-buffers-per-gate]({{< ref "docs/deployment/config" >}}#tas [...]
+4. 增大总的网络内存。目前网络内存的大小是比较保守的。对于大规模作业，为了实现更好的性能，建议将 [网络内存比例]({{< ref "docs/deployment/config" >}}#taskmanager-memory-network-fraction) 增加至至少 0.2。为了使调整生效，你可能需要同时调整 [网络内存大小下界]({{< ref "docs/deployment/config" >}}#taskmanager-memory-network-min) 以及 [网络内存大小上界]({{< ref "docs/deployment/config" >}}#taskmanager-memory-network-max)。要获取更多信息，你可以参考这个 [内存配置文档]({{< ref "docs/deployment/memory/mem_setup_tm" >}})。
+5. 增大数据写出内存。像上面提到的那样，对于大规模作业，如果有充足的空闲内存，建议增大 [数据写出内存]({{< ref "docs/deployment/config" >}}#taskmanager-network-sort-shuffle-min-buffers) 大小到至少 (2 * 并发数)。注意：在你增大这个配置后，为避免出现 "Insufficient number of network buffers" 错误，你可能还需要增大总的网络内存大小。
+6. 增大数据读取内存。像上面提到的那样，对于大规模作业，建议增大 [数据读取内存]({{< ref "docs/deployment/config" >}}#taskmanager-memory-framework-off-heap-batch-shuffle-size) 到一个较大的值 (比如，256M 或 512M)。因为这个内存是从框架的堆外内存切分出来的，因此你必须增加相同的内存大小到 [taskmanager.memory.framework.off-heap.size]({{< ref "docs/deployment/config" >}}#taskmanager-memory-framework-off-heap-size) 以避免出现直接内存溢出错误。
+
+## Trouble Shooting
+
+尽管十分罕见，下面列举了一些你可能会碰到的异常情况以及对应的处理策略：
+
+| 异常情况 | 处理策略 |
+| :--------- | :------------------ |
+| Insufficient number of network buffers | 这意味着网络内存大小不足以支撑作业运行，你需要增加总的网络内存大小。注意：从 1.15 开始，`Sort Shuffle` 已经成为默认实现，对于一些场景，`Sort Shuffle` 可能比 `Hash Shuffle` 需要更多的网络内存，因此当你的批作业升级到 1.15 以后可能会遇到这个网络内存不足的问题。这种情况下，你只需要增大总的网络内存大小即可。|
+| Too many open files | 这意味着文件句柄不够用了。如果你使用的是 `Hash Shuffle`，请切换到 `Sort Shuffle`。如果你已经在使用 `Sort Shuffle`，请考虑增大操作系统文件句柄上限并且检查是否是作业代码占用了过多的文件句柄。|
+| Connection reset by peer | 这通常意味着网络不太稳定或者压力较大。其他一些原因，比如上面提到的 SSL 握手超时等也可能会导致这一问题。如果你使用的是 `Hash Shuffle`，请切换到 `Sort Shuffle`。如果你已经在使用 `Sort Shuffle`，增大 [网络连接 backlog]({{< ref "docs/deployment/config" >}}#taskmanager-network-netty-server-backlog) 可能会有所帮助。|
+| Network connection timeout | 这通常意味着网络不太稳定或者压力较大。增大 [网络连接超时时间]({{< ref "docs/deployment/config" >}}#taskmanager-network-netty-client-connectTimeoutSec) 或者开启 [网络连接重试]({{< ref "docs/deployment/config" >}}#taskmanager-network-retries) 可能会有所帮助。|
+| Socket read/write timeout | 这通常意味着网络传输速度较慢或者压力较大。增大 [网络收发缓冲区]({{< ref "docs/deployment/config" >}}#taskmanager-network-netty-sendReceiveBufferSize) 大小可能会有所帮助。如果作业运行在 Kubernetes 环境，使用 [host network]({{< ref "docs/deployment/config" >}}#kubernetes-hostnetwork-enabled) 可能会有所帮助。|
+| Read buffer request timeout | 这个问题只会出现在 `Sort Shuffle`，它意味着对数据读取缓冲区的激烈竞争。要解决这一问题，你可以增大 [taskmanager.memory.framework.off-heap.batch-shuffle.size]({{< ref "docs/deployment/config" >}}#taskmanager-memory-framework-off-heap-batch-shuffle-size) 和 [taskmanager.memory.framework.off-heap.size]({{< ref "docs/deployment/config" >}}#taskmanager-memory-framework-off-heap-size)。|
+| No space left on device | 这通常意味着磁盘存储空间或者 inodes 被耗尽。你可以考虑扩展磁盘存储空间或者做一些数据清理。|
+| Out of memory error | 如果你使用的是 `Hash Shuffle`，请切换到 `Sort Shuffle`。如果你已经在使用 `Sort Shuffle` 并且遵循了上面章节的建议，你可以考虑增大相应的内存大小。对于堆上内存，你可以增大 [taskmanager.memory.task.heap.size]({{< ref "docs/deployment/config" >}}#ttaskmanager-memory-task-heap-size)，对于直接内存，你可以增大 [taskmanager.memory.task.off-heap.size]({{< ref "docs/deployment/config" >}}#taskmanager-memory-task-off-heap-size)。|
+| Container killed by external resource manger | 多种原因可能会导致容器被杀，比如，杀掉一个低优先级容器以释放资源启动高优先级容器，或者容器占用了过多的资源，比如内存、磁盘空间等。像上面章节所提到的那样，`Hash Shuffle` 可能会使用过多的内存而被 YARN 杀掉。所以，如果你使用的是 `Hash Shuffle`，请切换到 `Sort Shuffle`。如果你已经在使用 `Sort Shuffle`，你可能需要同时检查 Flink 日志以及资源管理框架的日志以找出容器被杀的根因，并且做出相应的修复。|
+
diff --git a/docs/content/docs/ops/batch/blocking_shuffle.md b/docs/content/docs/ops/batch/blocking_shuffle.md
index c6654f4..b3b4c9b 100644
--- a/docs/content/docs/ops/batch/blocking_shuffle.md
+++ b/docs/content/docs/ops/batch/blocking_shuffle.md
@@ -43,7 +43,7 @@ The default blocking shuffle implementation for 1.14 and lower, `Hash Shuffle`,
 
  - `file`: Writes files with the normal File IO, reads and transmits files with Netty `FileRegion`. `FileRegion` relies on `sendfile` system call to reduce the number of data copies and memory consumption.
  - `mmap`: Writes and reads files with `mmap` system call.
- - `Auto`: Writes files with the normal File IO, for file reading, it falls back to normal `file` option on 32 bit machine and use `mmap` on 64 bit machine. This is to avoid file size limitation of java `mmap` implementation on 32 bit machine.
+ - `auto`: Writes files with the normal File IO, for file reading, it falls back to normal `file` option on 32 bit machine and use `mmap` on 64 bit machine. This is to avoid file size limitation of java `mmap` implementation on 32 bit machine.
 
 The different mechanism could be chosen via [TaskManager configurations]({{< ref "docs/deployment/config#taskmanager-network-blocking-shuffle-type" >}}).
 
@@ -59,8 +59,6 @@ If [SSL]({{< ref "docs/deployment/security/security-ssl" >}}) is enabled, the `f
 The memory usage of `mmap` is not accounted for by configured memory limits, but some resource frameworks like Yarn will track this memory usage and kill the container if memory exceeds some threshold.
 {{< /hint >}}
 
-To further improve the performance, for most jobs we also recommend [enabling compression]({{< ref "docs/deployment/config">}}#taskmanager-network-blocking-shuffle-compression-enabled) unless the data is hard to compress.
-
 `Hash Shuffle` works well for small scale jobs with SSD, but it also have some disadvantages:
 
 1. If the job scale is large, it might create too many files, and it requires a large write buffer to write these files at the same time.
@@ -68,16 +66,14 @@ To further improve the performance, for most jobs we also recommend [enabling co
 
 ## Sort Shuffle 
 
-`Sort Shuffle` is another blocking shuffle implementation introduced in version 1.13 and it becomes the default blocking shuffle implementation in 1.15. Different from `Hash Shuffle`, sort shuffle writes only one file for each result partition. When the result partition is read by multiple downstream tasks concurrently, the data file is opened only once and shared by all readers. As a result, the cluster uses fewer resources like inode and file descriptors, which improves stability. Furt [...]
+`Sort Shuffle` is another blocking shuffle implementation introduced in version 1.13 and it becomes the default blocking shuffle implementation in 1.15. Different from `Hash Shuffle`, `Sort Shuffle` writes only one file for each result partition. When the result partition is read by multiple downstream tasks concurrently, the data file is opened only once and shared by all readers. As a result, the cluster uses fewer resources like inode and file descriptors, which improves stability. Fu [...]
 
-There are several config options that might need adjustment when using sort blocking shuffle:
-- [taskmanager.network.blocking-shuffle.compression.enabled]({{< ref "docs/deployment/config" >}}#taskmanager-network-blocking-shuffle-compression-enabled): Config option for shuffle data compression. it is suggested to enable it for most jobs except that the compression ratio of your data is low. Defaults to false for 1.14 and lower, and true for 1.15 and higher.
-- [taskmanager.network.sort-shuffle.min-parallelism]({{< ref "docs/deployment/config" >}}#taskmanager-network-sort-shuffle-min-parallelism): Config option to enable sort shuffle depending on the parallelism of downstream tasks. If parallelism is lower than the configured value, `hash shuffle` will be used, otherwise `sort shuffle` will be used. For versions lower than 1.15, its default value is `Integer.MAX_VALUE`, so hash shuffle will be always used by default. Since 1.15, its default v [...]
-- [taskmanager.network.sort-shuffle.min-buffers]({{< ref "docs/deployment/config" >}}#taskmanager-network-sort-shuffle-min-buffers): Config option to control data writing buffer size. For large scale jobs, you may need to increase this value, usually, several hundreds of megabytes memory is enough.
-- [taskmanager.memory.framework.off-heap.batch-shuffle.size]({{< ref "docs/deployment/config" >}}#taskmanager-memory-framework-off-heap-batch-shuffle-size): Config option to control data reading buffer size. For large scale jobs, you may need to increase this value, usually, several hundreds of megabytes memory is enough.
+Here are some config options that might need adjustment when using sort blocking shuffle:
+- [taskmanager.network.sort-shuffle.min-buffers]({{< ref "docs/deployment/config" >}}#taskmanager-network-sort-shuffle-min-buffers): Config option to control data writing buffer size. For large scale jobs, you may need to increase this value, usually, several hundreds of megabytes memory is enough. Because this memory is allocated from network memory, to increase this value, you may also need to increase the total network memory by adjusting [taskmanager.memory.network.fraction]({{< ref  [...]
+- [taskmanager.memory.framework.off-heap.batch-shuffle.size]({{< ref "docs/deployment/config" >}}#taskmanager-memory-framework-off-heap-batch-shuffle-size): Config option to control data reading buffer size. For large scale jobs, you may need to increase this value, usually, several hundreds of megabytes memory is enough. Because this memory is cut from the framework off-heap memory, to increase this value, you need also to increase the total framework off-heap memory by adjusting [taskm [...]
 
 {{< hint info >}}
-Currently `sort shuffle` only sort records by partition index instead of the records themselves, that is to say, the `sort` is only used as a data clustering algorithm.
+Currently `Sort Shuffle` only sort records by partition index instead of the records themselves, that is to say, the `sort` is only used as a data clustering algorithm.
 {{< /hint >}}
 
 ## Choices of Blocking Shuffle
@@ -85,5 +81,33 @@ Currently `sort shuffle` only sort records by partition index instead of the rec
 As a summary,
 
 - For small scale jobs running on SSD, both implementation should work.
-- For large scale jobs or for jobs running on HDD, `sort shuffle` should be more suitable.
-- In both case, you may consider [enabling compression]({{< ref "docs/deployment/config">}}#taskmanager-network-blocking-shuffle-compression-enabled) to improve the performance unless the data is hard to compress.
+- For large scale jobs or for jobs running on HDD, `Sort Shuffle` should be more suitable.
+
+To switch between `Sort Shuffle` and `Hash Shuffle`, you need to adjust this config option: [taskmanager.network.sort-shuffle.min-parallelism]({{< ref "docs/deployment/config" >}}#taskmanager-network-sort-shuffle-min-parallelism). It controls which shuffle implementation to use based on the parallelism of downstream tasks, if the parallelism is lower than the configured value, `Hash Shuffle` will be used, otherwise `Sort Shuffle` will be used. For versions lower than 1.15, its default va [...]
+
+## Performance Tuning
+
+The following guidelins may help you to achieve better performance especially for large scale batch jobs:
+
+1. Always use `Sort Shuffle` on HDD because `Sort Shuffle` can largely improve stability and IO performance. Since 1.15, `Sort Shuffle` is already the default blocking shuffle implementation, for 1.14 and lower version, you need to enable it manually by setting [taskmanager.network.sort-shuffle.min-parallelism]({{< ref "docs/deployment/config" >}}#taskmanager-network-sort-shuffle-min-parallelism) to 1.
+2. For both blocking shuffle implementations, you may consider [enabling data compression]({{< ref "docs/deployment/config">}}#taskmanager-network-blocking-shuffle-compression-enabled) to improve the performance unless the data is hard to compress. Since 1.15, data compression is already enabled by default, for 1.14 and lower version, you need to enable it manually.
+3. When `Sort Shuffle` is used, decreasing the number of [exclusive buffers per channel]({{< ref "docs/deployment/config" >}}#taskmanager-network-memory-buffers-per-channel) and increasing the number of [floating buffers per gate]({{< ref "docs/deployment/config" >}}#taskmanager-network-memory-floating-buffers-per-gate) can help. For 1.14 and higher version, it is suggested to set [taskmanager.network.memory.buffers-per-channel]({{< ref "docs/deployment/config" >}}#taskmanager-network-me [...]
+4. Increase the total size of network memory. Currently, the default network memory size is pretty modest. For large scale jobs, it's suggested to increase the total [network memory fraction]({{< ref "docs/deployment/config" >}}#taskmanager-memory-network-fraction) to at least 0.2 to achieve better performance. At the same time, you may also need to adjust the [lower bound]({{< ref "docs/deployment/config" >}}#taskmanager-memory-network-min) and [upper bound]({{< ref "docs/deployment/con [...]
+5. Increase the memory size for shuffle data write. As mentioned in the above section, for large scale jobs, it's suggested to increase the number of [write buffers per result partition]({{< ref "docs/deployment/config" >}}#taskmanager-network-sort-shuffle-min-buffers) to at least (2 * parallelism) if you have enough memory. Note that you may also need to increase the total size of network memory to avoid the "Insufficient number of network buffers" error after you increase this config value.
+6. Increase the memory size for shuffle data read. As mentioned in the above section, for large scale jobs, it's suggested to increase the size of the [shared read memory]({{< ref "docs/deployment/config" >}}#taskmanager-memory-framework-off-heap-batch-shuffle-size) to a larger value (for example, 256M or 512M). Because this memory is cut from the framework off-heap memory, you must increase [taskmanager.memory.framework.off-heap.size]({{< ref "docs/deployment/config" >}}#taskmanager-mem [...]
+
+## Trouble Shooting
+
+Here are some exceptions you may encounter (rarely) and the corresponding solutions that may help:
+
+| Exceptions | Potential Solutions |
+| :--------- | :------------------ |
+| Insufficient number of network buffers | This means the amount of network memory is not enough to run the target job and you need to increase the total network memory size. Note that since 1.15, `Sort Shuffle` has become the default blocking shuffle implementation and for some cases, it may need more network memory than before, which means there is a small possibility that your batch jobs may suffer from this issue after upgrading to 1.15. If this is the case, you just need to increase [...]
+| Too many open files | This means that the file descriptors is not enough. If you are using `Hash Shuffle`, please switch to `Sort Shuffle`. If you are already using `Sort Shuffle`, please consider increasing the system limit for file descriptor and check if the user code consumes too many file descriptors. |
+| Connection reset by peer | This usually means that the network is unstable or or under heavy burden. Other issues like SSL handshake timeout mentioned above may also cause this problem. If you are using `Hash Shuffle`, please switch to `Sort Shuffle`. If you are already using `Sort Shuffle`, increasing the [network backlog]({{< ref "docs/deployment/config" >}}#taskmanager-network-netty-server-backlog) may help. |
+| Network connection timeout | This usually means that the network is unstable or under heavy burden and increasing the [network connection timeout]({{< ref "docs/deployment/config" >}}#taskmanager-network-netty-client-connectTimeoutSec) or enable [connection retry]({{< ref "docs/deployment/config" >}}#taskmanager-network-retries) may help. |
+| Socket read/write timeout | This may indicate that the network is slow or under heavy burden and increasing the [network send/receive buffer size]({{< ref "docs/deployment/config" >}}#taskmanager-network-netty-sendReceiveBufferSize) may help. If the job is running in Kubernetes environment, using [host network]({{< ref "docs/deployment/config" >}}#kubernetes-hostnetwork-enabled) may also help. |
+| Read buffer request timeout | This can happen only when you are using `Sort Shuffle` and it means a fierce contention of the shuffle read memory. To solve the issue, you can increase [taskmanager.memory.framework.off-heap.batch-shuffle.size]({{< ref "docs/deployment/config" >}}#taskmanager-memory-framework-off-heap-batch-shuffle-size) together with [taskmanager.memory.framework.off-heap.size]({{< ref "docs/deployment/config" >}}#taskmanager-memory-framework-off-heap-size). |
+| No space left on device | This usually means that the disk space or the inodes have been exhausted. Please consider extending the storage space or do some cleanup. |
+| Out of memory error | If you are using `Hash Shuffle`, please switch to `Sort Shuffle`. If you are already using `Sort Shuffle` and following the above guidelines, please consider increasing the corresponding memory size. For heap memory, you can increase [taskmanager.memory.task.heap.size]({{< ref "docs/deployment/config" >}}#ttaskmanager-memory-task-heap-size) and for direct memory, you can increase [taskmanager.memory.task.off-heap.size]({{< ref "docs/deployment/config" >}}#taskmana [...]
+| Container killed by external resource manger | There are several reasons which can lead to the killing of a container, for example, kill a low priority container to make room for high priority container or the container uses too many resources like memory and disk space. As mentioned in the above section, `Hash Shuffle` may use too much memory and gets killed by YARN. So if you are using `Hash Shuffle`, please switch to `Sort Shuffle`. If `Sort Shuffle` is already used, you may need to [...]