Benjamin Mahler created MESOS-9336:
--------------------------------------
Summary: Hook interfaces and implementation performs excessive
protobuf copying.
Key: MESOS-9336
URL: https://issues.apache.org/jira/browse/MESOS-9336
Project: Mesos
Issue Type: Improvement
Components: modules
Reporter: Benjamin Mahler
The interfaces and implementation of hooks perform significant protobuf copying
and would benefit from copy elimination. Consider the case of the master task
label decorator:
https://github.com/apache/mesos/blob/1.7.0/src/hook/manager.cpp#L108-L138
{code}
Labels HookManager::masterLaunchTaskLabelDecorator(
const TaskInfo& taskInfo,
const FrameworkInfo& frameworkInfo,
const SlaveInfo& slaveInfo)
{
synchronized (mutex) {
// We need a mutable copy of the task info and set the new
// labels after each hook invocation. Otherwise, the last hook
// will be the only effective hook setting the labels.
TaskInfo taskInfo_ = taskInfo;
foreachpair (const string& name, Hook* hook, availableHooks) {
const Result<Labels> result =
hook->masterLaunchTaskLabelDecorator(
taskInfo_,
frameworkInfo,
slaveInfo);
// NOTE: If the hook returns None(), the task labels won't be
// changed.
if (result.isSome()) {
taskInfo_.mutable_labels()->CopyFrom(result.get());
} else if (result.isError()) {
LOG(WARNING) << "Master label decorator hook failed for module '"
<< name << "': " << result.error();
}
}
return taskInfo_.labels();
}
}
{code}
https://github.com/apache/mesos/blob/1.7.0/src/master/master.cpp#L5619-L5634
{code}
foreach (
TaskInfo& task, *message.mutable_task_group()->mutable_tasks()) {
taskIds.insert(task.task_id());
totalResources += task.resources();
addTask(task, framework, slave);
if (HookManager::hooksAvailable()) {
// Set labels retrieved from label-decorator hooks.
task.mutable_labels()->CopyFrom(
HookManager::masterLaunchTaskLabelDecorator(
task,
framework->info,
slave->info));
}
}
{code}
# We copy the entire task info.
# We copy the labels of the task info twice for each label decorator hook (the
hook itself has to copy all existing ones since the API will re-write the
labels, and then we copy the result back into the task info).
# We copy the labels back out to the caller.
# The master then copies the labels back into the task.
In the case of 1 hook, that's 1 copy of entire the task info (including labels)
and 4 copies of only the labels.
Without changing the interface, we can eliminate 3 of the label copying cases,
and we would be left with 1 copy of the entire task info (including labels),
and 1 copies of only the labels.
With changing the interface, we can achieve 0 copies. This can be done by
making it a mutation interface, or making it truly a label decorator (labels
can only be added) with the modification that hooks don't get to see the
additional labels added by previous hooks. These would all be breaking changes
that require adjusting hooks.
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