diff --git a/docs/content.zh/docs/deployment/tasks-scheduling/_index.md b/docs/content.zh/docs/deployment/tasks-scheduling/_index.md new file mode 100644 index 0000000000000..06fbdd801c4a3 --- /dev/null +++ b/docs/content.zh/docs/deployment/tasks-scheduling/_index.md @@ -0,0 +1,23 @@ +--- +title: Tasks Scheduling +bookCollapseSection: true +weight: 9 +--- + diff --git a/docs/content.zh/docs/deployment/tasks-scheduling/balanced_tasks_scheduling.md b/docs/content.zh/docs/deployment/tasks-scheduling/balanced_tasks_scheduling.md new file mode 100644 index 0000000000000..6d7d287cd5029 --- /dev/null +++ b/docs/content.zh/docs/deployment/tasks-scheduling/balanced_tasks_scheduling.md @@ -0,0 +1,118 @@ +--- +title: Balanced Tasks Scheduling +weight: 5 +type: docs + +--- + + +# Balanced Tasks Scheduling + +This page describes the background and principle of balanced tasks scheduling, +how to use it when running streaming jobs. + +## Background + +When the parallelism of all vertices within a Flink streaming job is inconsistent, +the [default strategy]({{< ref "docs/deployment/config" >}}#taskmanager-load-balance-mode) +of Flink to deploy tasks sometimes leads some `TaskManagers` have more tasks while others have fewer tasks, +resulting in excessive resource utilization at some `TaskManagers` +that contain more tasks and becoming a bottleneck for the entire job processing. + +{{< img src="/fig/deployments/tasks-scheduling/tasks_scheduling_skew_case.svg" alt="The Skew Case of Tasks Scheduling" class="offset" width="50%" >}} + +As shown in figure (a), given a Flink job comprising two vertices, `JobVertex-A (JV-A)` and `JobVertex-B (JV-B)`, +with parallelism degrees of `6` and `3` respectively, +and both vertices sharing the same slot sharing group. +Under the default tasks scheduling strategy, as illustrated in figure (b), +the distribution of tasks across `TaskManagers` may result in significant disparities in task load. +Specifically, the `TaskManager`s with the highest number of tasks may host `4` tasks, +while the one with the lowest load may have only `2` tasks. +Consequently, the `TaskManager`s bearing 4 tasks is prone to become a performance bottleneck for the entire job. + +Therefore, Flink provides a task-quantity-based balanced tasks scheduling capability. +Within the job's resource view, it aims to ensure that the number of tasks +scheduled to each `TaskManager` as close as possible to, thereby improving the resource usage skew among `TaskManagers`. + +## Principle + +The task-quantity-based load balancing tasks scheduling strategy completes the assignment of tasks to `TaskManagers` in two phases: +- The tasks-to-slots assignment phase +- The slots-to-TaskManagers assignment phase + +This section will use two examples to illustrate the simplified process and principle of +how the task-quantity-based tasks scheduling strategy handles the assignments in these two phases. + +### The tasks-to-slots assignment phase + +Taking the job shown in figure (c) as an example, it contains five job vertices with parallelism degrees of `1`, `4`, `4`, `2`, and `3`, respectively. +All five job vertices belong to the default slot sharing group. + +{{< img src="/fig/deployments/tasks-scheduling/tasks_to_slots_allocation_principle.svg" alt="The Tasks To Slots Allocation Principle Demo" class="offset" width="65%" >}} + +During the tasks-to-slots assignment phase, this tasks scheduling strategy: +- First directly assigns the tasks of the vertices with the highest parallelism to the `i-th` slot. + + That is, task `JV-Bi` is assigned directly to `sloti`, and task `JV-Ci` is assigned directly to `sloti`. + +- Next, for tasks belonging to job vertices with sub-maximal parallelism, they are assigned in a round-robin fashion across the slots within the current +slot sharing group until all tasks are allocated. + +As shown in figure (e), under the task-quantity-based assignment strategy, the range (max-min difference) of the number of tasks per slot is `1`, +which is better than the range of `3` under the default strategy shown in figure (d). + +Thus, this ensures a more balanced distribution of the number of tasks across slots. + +### The slots-to-TaskManagers assignment phase + +As shown in figure (f), given a Flink job comprising two vertices, `JV-A` and `JV-B`, with parallelism of `6` and `3` respectively, +and both vertices sharing the same slot sharing group. + +{{< img src="/fig/deployments/tasks-scheduling/slots_to_taskmanagers_allocation_principle.svg" alt="The Slots to TaskManagers Allocation Principle Demo" class="offset" width="75%" >}} + +The assignment result after the first phase is shown in figure (g), +where `Slot0`, `Slot1`, and `Slot2` each contain `2` tasks, while the remaining slots contain `1` task each. + +Subsequently: +- The strategy submits all slot requests and waits until all slot resources required for the current job are ready. + +Once the slot resources are ready: +- The strategy then sorts all slot requests in descending order based on the number of tasks contained in each request. +Afterwards, it sequentially assigns each slot request to the `TaskManager` with the smallest current tasks loading. +This process continues until all slot requests have been allocated. + +The final assignment result is shown in figure (i), where each `TaskManager` ends up with exactly `3` tasks, +resulting in a task count difference of `0` between `TaskManagers`. In contrast, the scheduling result under the default strategy, +shown in figure (h), has a task count difference of `2` between `TaskManagers`. + +Therefore, theoretically, using this load balancing tasks scheduling strategy could effectively mitigate the issue of +resource usage skew caused by significant disparities in the number of tasks across `TaskManagers` . + +## Usage + +You can enable balanced tasks scheduling through the following configuration item: + +- `taskmanager.load-balance.mode`: `tasks` + +## More details + +See the FLIP-370 for more details. + +{{< top >}} diff --git a/docs/content/docs/deployment/tasks-scheduling/_index.md b/docs/content/docs/deployment/tasks-scheduling/_index.md new file mode 100644 index 0000000000000..06fbdd801c4a3 --- /dev/null +++ b/docs/content/docs/deployment/tasks-scheduling/_index.md @@ -0,0 +1,23 @@ +--- +title: Tasks Scheduling +bookCollapseSection: true +weight: 9 +--- + diff --git a/docs/content/docs/deployment/tasks-scheduling/balanced_tasks_scheduling.md b/docs/content/docs/deployment/tasks-scheduling/balanced_tasks_scheduling.md new file mode 100644 index 0000000000000..6d7d287cd5029 --- /dev/null +++ b/docs/content/docs/deployment/tasks-scheduling/balanced_tasks_scheduling.md @@ -0,0 +1,118 @@ +--- +title: Balanced Tasks Scheduling +weight: 5 +type: docs + +--- + + +# Balanced Tasks Scheduling + +This page describes the background and principle of balanced tasks scheduling, +how to use it when running streaming jobs. + +## Background + +When the parallelism of all vertices within a Flink streaming job is inconsistent, +the [default strategy]({{< ref "docs/deployment/config" >}}#taskmanager-load-balance-mode) +of Flink to deploy tasks sometimes leads some `TaskManagers` have more tasks while others have fewer tasks, +resulting in excessive resource utilization at some `TaskManagers` +that contain more tasks and becoming a bottleneck for the entire job processing. + +{{< img src="/fig/deployments/tasks-scheduling/tasks_scheduling_skew_case.svg" alt="The Skew Case of Tasks Scheduling" class="offset" width="50%" >}} + +As shown in figure (a), given a Flink job comprising two vertices, `JobVertex-A (JV-A)` and `JobVertex-B (JV-B)`, +with parallelism degrees of `6` and `3` respectively, +and both vertices sharing the same slot sharing group. +Under the default tasks scheduling strategy, as illustrated in figure (b), +the distribution of tasks across `TaskManagers` may result in significant disparities in task load. +Specifically, the `TaskManager`s with the highest number of tasks may host `4` tasks, +while the one with the lowest load may have only `2` tasks. +Consequently, the `TaskManager`s bearing 4 tasks is prone to become a performance bottleneck for the entire job. + +Therefore, Flink provides a task-quantity-based balanced tasks scheduling capability. +Within the job's resource view, it aims to ensure that the number of tasks +scheduled to each `TaskManager` as close as possible to, thereby improving the resource usage skew among `TaskManagers`. + +## Principle + +The task-quantity-based load balancing tasks scheduling strategy completes the assignment of tasks to `TaskManagers` in two phases: +- The tasks-to-slots assignment phase +- The slots-to-TaskManagers assignment phase + +This section will use two examples to illustrate the simplified process and principle of +how the task-quantity-based tasks scheduling strategy handles the assignments in these two phases. + +### The tasks-to-slots assignment phase + +Taking the job shown in figure (c) as an example, it contains five job vertices with parallelism degrees of `1`, `4`, `4`, `2`, and `3`, respectively. +All five job vertices belong to the default slot sharing group. + +{{< img src="/fig/deployments/tasks-scheduling/tasks_to_slots_allocation_principle.svg" alt="The Tasks To Slots Allocation Principle Demo" class="offset" width="65%" >}} + +During the tasks-to-slots assignment phase, this tasks scheduling strategy: +- First directly assigns the tasks of the vertices with the highest parallelism to the `i-th` slot. + + That is, task `JV-Bi` is assigned directly to `sloti`, and task `JV-Ci` is assigned directly to `sloti`. + +- Next, for tasks belonging to job vertices with sub-maximal parallelism, they are assigned in a round-robin fashion across the slots within the current +slot sharing group until all tasks are allocated. + +As shown in figure (e), under the task-quantity-based assignment strategy, the range (max-min difference) of the number of tasks per slot is `1`, +which is better than the range of `3` under the default strategy shown in figure (d). + +Thus, this ensures a more balanced distribution of the number of tasks across slots. + +### The slots-to-TaskManagers assignment phase + +As shown in figure (f), given a Flink job comprising two vertices, `JV-A` and `JV-B`, with parallelism of `6` and `3` respectively, +and both vertices sharing the same slot sharing group. + +{{< img src="/fig/deployments/tasks-scheduling/slots_to_taskmanagers_allocation_principle.svg" alt="The Slots to TaskManagers Allocation Principle Demo" class="offset" width="75%" >}} + +The assignment result after the first phase is shown in figure (g), +where `Slot0`, `Slot1`, and `Slot2` each contain `2` tasks, while the remaining slots contain `1` task each. + +Subsequently: +- The strategy submits all slot requests and waits until all slot resources required for the current job are ready. + +Once the slot resources are ready: +- The strategy then sorts all slot requests in descending order based on the number of tasks contained in each request. +Afterwards, it sequentially assigns each slot request to the `TaskManager` with the smallest current tasks loading. +This process continues until all slot requests have been allocated. + +The final assignment result is shown in figure (i), where each `TaskManager` ends up with exactly `3` tasks, +resulting in a task count difference of `0` between `TaskManagers`. In contrast, the scheduling result under the default strategy, +shown in figure (h), has a task count difference of `2` between `TaskManagers`. + +Therefore, theoretically, using this load balancing tasks scheduling strategy could effectively mitigate the issue of +resource usage skew caused by significant disparities in the number of tasks across `TaskManagers` . + +## Usage + +You can enable balanced tasks scheduling through the following configuration item: + +- `taskmanager.load-balance.mode`: `tasks` + +## More details + +See the FLIP-370 for more details. + +{{< top >}} diff --git a/docs/static/fig/deployments/tasks-scheduling/slots_to_taskmanagers_allocation_principle.svg b/docs/static/fig/deployments/tasks-scheduling/slots_to_taskmanagers_allocation_principle.svg new file mode 100644 index 0000000000000..9a9e4ccab21ac --- /dev/null +++ b/docs/static/fig/deployments/tasks-scheduling/slots_to_taskmanagers_allocation_principle.svg @@ -0,0 +1,451 @@ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + diff --git a/docs/static/fig/deployments/tasks-scheduling/tasks_scheduling_skew_case.svg b/docs/static/fig/deployments/tasks-scheduling/tasks_scheduling_skew_case.svg new file mode 100644 index 0000000000000..123c9b43944f4 --- /dev/null +++ b/docs/static/fig/deployments/tasks-scheduling/tasks_scheduling_skew_case.svg @@ -0,0 +1,246 @@ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + diff --git a/docs/static/fig/deployments/tasks-scheduling/tasks_to_slots_allocation_principle.svg b/docs/static/fig/deployments/tasks-scheduling/tasks_to_slots_allocation_principle.svg new file mode 100644 index 0000000000000..c35f4f429d9be --- /dev/null +++ b/docs/static/fig/deployments/tasks-scheduling/tasks_to_slots_allocation_principle.svg @@ -0,0 +1,531 @@ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +