sorter: fix panic when getting memory pressure fails

[liuzix]

What problem does this PR solve?

• When /proc/meminfo fails to open, TiCDC will panic because of inappropriate error handling. This usually happens when the OS does not allow TiCDC any more file descriptors.

What is changed and how it works?

• Fixed error handling when reading system memory pressure.

Check List

Tests

• Unit test

Related changes

• Need to cherry-pick to the release branch

Release note

• Fix panic when TiCDC fails to read /proc/meminfo

[liuzix]

/run-all-tests

[liuzix]

/run-unit-test

[liuzix]

/run-unit-tests

[ti-chi-bot]

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[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• amyangfei
• overvenus

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[overvenus]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 47b2559

[amyangfei]

/run-kafka-tests
/run-integration-tests

[overvenus]

/run-kafka-tests

[codecov-commenter]

Codecov Report

Merging #2014 (3c29b23) into master (b6d58ef) will decrease coverage by 0.3065%.
The diff coverage is 64.3364%.

@@               Coverage Diff                @@
##             master      #2014        +/-   ##
================================================
- Coverage   54.0780%   53.7714%   -0.3066%     
================================================
  Files           156        164         +8     
  Lines         16589      17394       +805     
================================================
+ Hits           8971       9353       +382     
- Misses         6667       7065       +398     
- Partials        951        976        +25     

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #2023.

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #2024.

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #2025.