Benjamin Mahler created MESOS-6765:
--------------------------------------
Summary: Consider making the Resources wrapper "copy-on-write" to
improve performance.
Key: MESOS-6765
URL: https://issues.apache.org/jira/browse/MESOS-6765
Project: Mesos
Issue Type: Improvement
Reporter: Benjamin Mahler
Resources currently directly stores the underlying resource objects:
{code}
class Resources
{
...
std::vector<Resource_> resources;
};
{code}
What this means is that copying of Resources (which occurs frequently) is
expensive since copying a {{Resource}} object is relatively heavy-weight.
One strategy, in MESOS-4770, is to avoid protobuf in favor of C++ types (i.e.
replace {{Value::Scalar}}, {{Value::Set}}, and {{Value::Ranges}} with C++
equivalents). However, metadata like reservations, disk info, etc, is still
fairly expensive to copy even if avoiding protobufs.
An approach to reduce copying would be to only copy the resource objects upon
writing, when there are multiple references to the resource object. If there is
a single reference to the resource object we could safely mutate it without
copying. E.g.
{code}
class Resource
{
...
std::vector<shared_ptr<Resource_>> resources;
};
// Mutation function:
void Resources::mutate(size_t index)
{
// Copy if there are multiple references.
if (resources[i].use_count() > 1) {
resources[i] = copy(resources[i]);
}
// Mutate safely.
resources[i].some_mutation();
}
{code}
On the other hand, this introduces a additional level of pointer chasing. So we
would need to weigh the approaches.
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