add session tool to manage and analysis sessions

[carrey-feng]

What type of PR is this?

• bug
• feature
• enhancement

What problem(s) does this PR solve?

Issue(s) number:

Description:
Metad OOM because some users have frequently created sessions and did not release those sessions.
Finally by more than 8000000 sessions were created. When I tried to restart cluster, metad OOM occured again.
I found that graphd/storaged called waitForMetadReady function of MetaClient to wait for Metad become be available,
Metad loaded all sessions to memory in waitForMetadReady function. Too many sessions caused metad OOM.

How do you solve it?

I develop a session tool to delete extra sessions in the way offline. It directly delete sessions from rocksdb data of all metad after cluster shutdown. It can delete all sessions and delete the sessions for the specified user. like this:

delete all sessions:
session_tool -path data/meta/nebula/0/data -operator delete (need execute it on every metad node)

delete all sessions of root user:
session_tool -path data/meta/nebula/0/data -operator delete -user root (need execute it on every metad node)

In addition it also counts the number of sessions in rocksdb of metad in real time, like this:
The total number of sessions in cluster：
session_tool -path data/meta/nebula/0/data -operator count

The number of sessions per user:
session_tool -path data/meta/nebula/0/data -operator groupCount

It can also show sessions info, like this:
Show N sessions：
session_tool -path data/meta/nebula/0/data -operator list -limit N

Show N sessions of user root:
session_tool -path data/meta/nebula/0/data -operator list -limit N -user root

Special notes for your reviewer, ex. impact of this fix, design document, etc:

Checklist:

Tests:

• Unit test(positive and negative cases)
• Function test
• Performance test
• N/A

Affects:

• Documentation affected (Please add the label if documentation needs to be modified.)
• Incompatibility (If it breaks the compatibility, please describe it and add the label.）
• If it's needed to cherry-pick (If cherry-pick to some branches is required, please label the destination version(s).)
• Performance impacted: Consumes more CPU/Memory

Release notes:

Please confirm whether to be reflected in release notes and how to describe:

add a session tool to manage and analysis sessions

[CLAassistant]

All committers have signed the CLA.

[Hera-han]

@CPWstatic this PR has been open for a long time, please take a look and give feedback. thanks~

[darionyaphet]

why don't use std::unordered_map<std::string, int> map directly?

[darionyaphet]

why don't merge sessionsCount and deleteSession into one ?

[CPWstatic]

The session could be manipulated via admin command. We support read sessions for now, i suggest you implement a delete command rather than a tool.

[carrey-feng]

The session could be manipulated via admin command. We support read sessions for now, i suggest you implement a delete command rather than a tool.

@CPWstatic
Too many sessions causing Metad OOM. Cluster can't start normally，admin command can not be used before cluster is available. I can only use offline repair mode to delete sessions to ensure that the cluster is started normally. You can get the reason for the cluster cannot be started normally from issue description

[xtcyclist]

This PR has been opened for too long. It is addressing a valid problem, although I'm not sure whether this problem is still there after almost a year. I've rebased the PR to check the CI results.

[xtcyclist]

Given that the CI here run into errors and this issue has been opened for too long, I'm closing this PR fow now. It is welcomed for anyone to pick this up later, fix related issues, and reopen it.