feat(tdigest): implement tdigest.cdf command

[LindaSummer]

Issue

Close #2807

Proposed Changes

• Implement tdigest.cdf command
• Add unit tests and integration tests

[Copilot]

Pull request overview

This PR adds Redis-compatible support for the TDIGEST.CDF command to Kvrocks’ TDigest feature set (issue #2807), along with new C++ unit tests and Go integration tests to validate behavior against Redis.

Changes:

• Add TDigest::CDF API and implementation in the TDigest type layer.
• Register and implement the tdigest.cdf command handler.
• Add Go and C++ tests covering argument validation, empty-digest behavior, and sample-based correctness.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
tests/gocase/unit/type/tdigest/tdigest_test.go	Adds Go integration tests for TDIGEST.CDF including empty/non-empty digests and Redis-sourced samples.
tests/cppunit/types/tdigest_test.cc	Adds C++ unit tests for TDigest::CDF across several distributions and edge cases.
src/types/redis_tdigest.h	Introduces TDigestCDFResult and the TDigest::CDF API.
src/types/redis_tdigest.cc	Implements the TDigest::CDF computation over stored centroids/buffers.
src/commands/cmd_tdigest.cc	Adds the tdigest.cdf command implementation and registers it.

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[Copilot]

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

[Copilot]

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated 10 comments.

[jihuayu]

The CDF algorithm in this PR differs from Redis’s implementation. Was this intentional?

TDIGEST.CREATE t COMPRESSION 10
TDIGEST.ADD t 0 1 2 ... 99
TDIGEST.CDF t 20 40 50 60 80

Query	RedisBloom	this PR
20	0.205	0.09
40	0.405	0.33
50	0.505	0.63
60	0.605	0.63
80	0.805	0.88

[LindaSummer]

The CDF algorithm in this PR differs from Redis’s implementation. Was this intentional?

TDIGEST.CREATE t COMPRESSION 10
TDIGEST.ADD t 0 1 2 ... 99
TDIGEST.CDF t 20 40 50 60 80

Query RedisBloom this PR
20 0.205 0.09
40 0.405 0.33
50 0.505 0.63
60 0.605 0.63
80 0.805 0.88

Hi @jihuayu ,

Thanks very much for your checking! ❤️
Kvrocks result should align with Redis's, at least should not have such a clear difference.

I will investigate the problem and find the root cause.

[LindaSummer]

Hi @jihuayu ,

Thanks very much for your correction and review.

This problem is caused by the missing of interpolation of CDF value.
I have followed the redisbloom implementation and the latest patch's result should be aligned with redis now.

== compressed centroids setup ==
$ redis-cli -h 127.0.0.1 -p 6666 TDIGEST.CREATE kvrocks_check-1:compressed COMPRESSION 10
OK

== compressed centroids add 0..99 ==
$ redis-cli -h 127.0.0.1 -p 6666 TDIGEST.ADD kvrocks_check-1:compressed 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99
OK

== compressed centroids cdf, expected Redis-like: 0.205 0.405 0.505 0.605 0.805 ==
$ redis-cli -h 127.0.0.1 -p 6666 TDIGEST.CDF kvrocks_check-1:compressed 20 40 50 60 80
0.20499999999999999
0.40500000000000003
0.505
0.60499999999999998
0.80500000000000005

[jihuayu]

@LindaSummer It doesn’t seem to be aligned. (We have two '7')

TDIGEST.CREATE t COMPRESSION 200
TDIGEST.ADD t -40 -36 -27 -13 -12 7 7 25 47 50
TDIGEST.CDF t 0 6.9 7 7.1 10

query	RedisBloom	Kvrocks PR
0	0.5	0.5631578947
6.9	0.5	0.5994736842
7	0.6	0.6
7.1	0.7	0.6005555556
10	0.7	0.6166666667

[sonarqubecloud]

Quality Gate passed

Issues
2 New issues
0 Accepted issues

Measures
0 Security Hotspots
53.6% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[LindaSummer]

@LindaSummer It doesn’t seem to be aligned. (We have two '7')

TDIGEST.CREATE t COMPRESSION 200
TDIGEST.ADD t -40 -36 -27 -13 -12 7 7 25 47 50
TDIGEST.CDF t 0 6.9 7 7.1 10

query RedisBloom Kvrocks PR
0 0.5 0.5631578947
6.9 0.5 0.5994736842
7 0.6 0.6
7.1 0.7 0.6005555556
10 0.7 0.6166666667

Hi @jihuayu ,

Thanks for your review and patience! ❤️

I will fix this problem and add more cases to full cover the core logic.