http_status: add the http api for ballast object

[hnes]

What problem does this PR solve?

Problem Summary:

Try to reduce the GC frequency on some occasions.

What is changed and how it works?

What's Changed:

Add a ballast object.

How it Works:

Here are some articles and documentation.

SetGCPercent

Go memory ballast: How I learnt to stop worrying and love the heap

proposal: runtime: add a mechanism for specifying a minimum target heap size

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

# get current size of the ballast object
curl -v 127.0.0.1:10080/debug/ballast-object-sz
# reset the size of the ballast object (2GB in this example)
curl -v -d "2147483648" -X POST 127.0.0.1:10080/debug/ballast-object-sz

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Add http api for the ballast object.

[CLAassistant]

All committers have signed the CLA.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• coocood
• tiancaiamao

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[tiancaiamao]

It seems the CI environment is not using go 1.16

[purelind]

/rebuild

[purelind]

/rebuild

[youjiali1995]

What if the heap size reaches the two times of the ballast size? Can the GC affect performance a lot?

[coocood]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 05e6ac5

[hnes]

What if the heap size reaches the two times of the ballast size? Can the GC affect performance a lot?

Basically, Golang's GC has two phases: mark and sweep.

C1: Sweep is a very fast operation, and the time cost of GC is largely dominated by the mark phase, not the sweep.

C2: The time cost of the mark phase in GC is mainly depending on the amount of the living objects and has very little to do with the amount of unused objects.

So above all, when the heap size reaches the two times of the ballast size:

• It would not influence the time cost of GC's mark phase very much because of C2.

• It would bring more pressure to the weep phase, but it would be acceptable because of C1.