karmada-metrics-adapter: reduce memory usage

[chaunceyjiang]

When there is a large amount of pod usage in the member cluster, metrics-adapter will consume a lot of memory. The reason is that it caches all the information of all pods in the cluster. However, we don't need all this information, so we trim some of the information to reduce memory usage.

What type of PR is this? /kind bug

What this PR does / why we need it:

Which issue(s) this PR fixes: Fixes #

Special notes for your reviewer:

The core idea of this PR is to use TransformFunc to trim the fields that pod and node need to buffer. Currently, it only retains fields such as name, namespace, labels, etc. Other fields are not needed, so we do not need to cache them.

Does this PR introduce a user-facing change?:

karmada-metrics-adapter: reduce memory usage

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[chaosi-zju]

We have tested on such environment: 2 member clusters, each cluster have 500 node, 10000 pod in all.

before this PR introduced: karmada-metrics-adapter cost 1.3GB memory at least (and may probabilistically rise), memory overhead is mainly due to the line _ = sci.Lister(provider.PodsGVR).

after this PR introduced: only cost about 300MB.

This is a significant performance optimization ! ٩(๑❛ᴗ❛๑)۶

[chaosi-zju]

Now, can you add more explaination in PR description to summarize how does this PR works to reduce the memory?

You only said you trimmed some of the information, may be you can explain more about why typedmanager is better than genericmanager, or other summary terms.

[chaosi-zju]

/LGTM

[XiShanYongYe-Chang]

It's probably more of a feature. /kind feature /lgtm

[karmada-bot]

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