Add the support of the LCS command

[JoverZhang]

Close #1955

[jihuayu]

Thank you @JoverZhang, wonderful algorithm.
I think it's not good to put so much logic in the commander.
Would it be better to move the specific logic to redis::String? @git-hulk

[mapleFU]

I didn't review the logic for response, just some few comments

[jihuayu]

Can someone confirm whether this logic is correct? I am also unable to determine it.
Alternatively, can we ignore whether the algorithm is correct and fix it when a bug arises?

[mapleFU]

General LGTM. Just some few nits

@jihuayu Actually I think this impl works(Since it's code it's similiar with Redis' impl). However, I think the most important thing is prevent malicious user from using lcs to attack the system, or lcs making the server crash...

[PragmaTwice]

As mentioned by @jihuayu, the implementation of the algorithm should be put into redis_string.cc instead of cmd_string.cc.

[JoverZhang]

As mentioned by @jihuayu, the implementation of the algorithm should be put into redis_string.cc instead of cmd_string.cc.

Understood, I have moved the algorithm to redis_string.cc as suggested. Please review the implementation and let me know if any further modifications are required.

[mapleFU]

General LGTM

[mapleFU]

Though I don't think performance of LCS it's important, I think deque or vector ( using vector without pop_front) would be better here.

[PragmaTwice]

Yeah, deque or vector is better here.

[JoverZhang]

Thank. I have modified this to use the vector.

Initially, I hadn't used the vector because I was concerned that a very large vector would significantly increase memory usage when building the output at the end.
However, I forgot that dp actually frees up more memory space at the end of string_db.LCS().

[mapleFU]

LGTM

[sonarqubecloud]

Quality Gate failed

Failed conditions
9.4% Duplication on New Code (required ≤ 5%)

See analysis details on SonarCloud

[PragmaTwice]

Thank you for your contribution!

[jihuayu]

Hi @JoverZhang, can you add this command to our docs?
You can set Since Version with unstable.
https://kvrocks.apache.org/docs/supported-commands#string-commands

[JoverZhang]

Hi @JoverZhang, can you add this command to our docs? You can set Since Version with unstable. https://kvrocks.apache.org/docs/supported-commands#string-commands

Okay, I added it.
apache/kvrocks-website#208