GetDstBySrc

[critical27]

What type of PR is this?

• bug
• feature
• enhancement

What problem(s) does this PR solve?

Issue(s) number:

Subtask of #4525

Description:

Add a new rpc interface called GetDstBySrc, the difference between it and GetNeighbors is that it only return dst of the edge in each row (even the srcId is not returned), see the interface in storage.thrift for details. And the dst has been deduped before returned to graphd to minimize memory cost.

How do you solve it?

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:

ex. Fixed the bug .....

[jievince]

LGTM

[Shylock-Hg]

nebula::Row is more clear.

[Shylock-Hg]

Why remove this?

[wenhaocs]

The same Q

[critical27]

They have been check on a higher level node, this is redundant. All the check only exists in output node, just to keep unify with others

[pengweisong]

Good job

[wenhaocs]

Generally, can you reuse getNeighbors but make kVid optional, ie. set kVid only when it's specified in req?

[jievince]

ee the interfac

They are different in memory occupation. See https://confluence.nebula-graph.io/pages/viewpage.action?pageId=47392379

[wenhaocs]

ee the interfac

They are different in memory occupation. See https://confluence.nebula-graph.io/pages/viewpage.action?pageId=47392379

The response seems like the same:

vs.

The only difference is in request. But you can mark only returning kDst in the request.

[jievince]

GetNeighbors takes up more memory.

[critical27]

Generally, can you reuse getNeighbors but make kVid optional, ie. set kVid only when it's specified in req?

We could indeed, there are several slight difference between them:

1. return format as @jievince mentioned
2. the StoragePlan is simplified for GetDstBySrc
3. the output has been deduped in GetDstBySrc, which we don't do it in getNeighbors
4. most of all, this interface is used for the interim result for the first (N - 1) steps in go N steps, if we reuse GetNeighbors, the impact will be not be trival

[dutor]

LGTM.