Fix loading old logit model, helper for converting old pickle.

[trivialfis]

Continue #5277 . But PR against 1.0.0 branch. Fixes #5276 .

• Remove saving metric in binary model.
• Save a JSON string for objective.
• Save a version string in binary model.
• Distinguish model before 1.0 and after 1.0.
• More tests for model compatibility.

[trivialfis]

I will port the related changes to master. PR against release branch so we can run the tests.

[trivialfis]

A batch of models with 0.90:

models.zip

[trivialfis]

Phew ...

[trivialfis]

@RAMitchell @hcho3 Please review. ;-)

[trivialfis]

Wait, still got some test failures on my end.

[trivialfis]

@hcho3 I will generate a new batch of models including both 0.90 and 1.0.0. Can we upload it to some where, like Jenkins or maybe github has small data storage (like release meta data)?

[hcho3]

We can put them in an S3 bucket. Jenkins can access all S3 buckets in the same AWS account. Can you send me the models?

[trivialfis]

models.zip

[hcho3]

@trivialfis The zip file is available at s3://xgboost-ci-jenkins-artifacts/xgboost_model_compatibility_test.zip. You can use boto3 package in Python to download the zip file:

import boto3

s3_bucket = boto3.resource('s3').Bucket('xgboost-ci-jenkins-artifacts')
s3_bucket.download_file('xgboost_model_compatibility_test.zip',
                        './xgboost_model_compatibility_test.zip')

Any Jenkins worker should be able to run this line.

[trivialfis]

@hcho3 I updated the test to download the models, please review.

[hcho3]

Thanks for adding model compatibility checks. The checks will ensure backward compatibility moving forward.

[trivialfis]

A similar issue is also found in treelite. Will try to fix it. It may be worth documenting in release note that everyone who reads the binary model needs to adjust, and it's encouraged to try the experimental JSON support and provide feedbacks.

[trivialfis]

This seems somehow breaks treelite.

[hcho3]

Do you need help with fixing the build?

[trivialfis]

I need to figure out a way to disable this auto include.

[RAMitchell]

LGTM. Hope we don't have to maintain these fixes for long :)

[mli]

Codecov Report

Merging #5281 into release_1.0.0 will not change coverage by %.
The diff coverage is n/a.

@@              Coverage Diff               @@
##           release_1.0.0    #5281   +/-   ##
==============================================
  Coverage          83.83%   83.83%           
==============================================
  Files                 11       11           
  Lines               2413     2413           
==============================================
  Hits                2023     2023           
  Misses               390      390           

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 5ca21f2...f482c9d. Read the comment docs.

[trivialfis]

Will port it to master branch.