VIndexes: Stop recommending md5 based vindex types as md5 is considered insecure

[mattlord]

Description

When creating the vtctldclient implementation of the LookupVindex command in #14086, I added the ability to specify which vindex type to use with the --table-vindex-type flag. The vtctlclient client and its behavior is now frozen as it's deprecated and slated for removal so that will not be modified.

By default, however, we would still use md5 by default for text based column types (we had changed the default/recommended vindex type for integral column types in #13955 and #13956). This PR moves the md5 based recommendations to xxhash based ones as md5 for passwords is considered insecure (1, 2, 3, ...) so any usage of it in your fleet — even though with Vindexes it is NOT used for passwords — can trigger security warnings on audits. Beyond that, xxhash should generally be faster as well. So we should recommend it as the default instead.

Related Issue(s)

• Follow-up to:
  • CreateLookupVindex should use xxhash for integer types #13955
  • Change internal vindex type recommendation for integrals to xxhash #13956
• Fixes: Feature Request: Allow setting the hashing used for lookup vindexes in CreateLookupVindex #14155

Checklist

• "Backport to:" labels have been added if this change should be back-ported to release branches
• If this change is to be back-ported to previous releases, a justification is included in the PR description
• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on CI?
• Documentation: Replace recommendations/samples using md5 and hash with xxhash website#1772

[vitess-bot]

Review Checklist

Hello reviewers! 👋 Please follow this checklist when reviewing this Pull Request.

General

• Ensure that the Pull Request has a descriptive title.
• Ensure there is a link to an issue (except for internal cleanup and flaky test fixes), new features should have an RFC that documents use cases and test cases.

Tests

• Bug fixes should have at least one unit or end-to-end test, enhancement and new features should have a sufficient number of tests.

Documentation

• Apply the release notes (needs details) label if users need to know about this change.
• New features should be documented.
• There should be some code comments as to why things are implemented the way they are.
• There should be a comment at the top of each new or modified test to explain what the test does.

New flags

• Is this flag really necessary?
• Flag names must be clear and intuitive, use dashes (-), and have a clear help text.

If a workflow is added or modified:

• Each item in Jobs should be named in order to mark it as required.
• If the workflow needs to be marked as required, the maintainer team must be notified.

Backward compatibility

• Protobuf changes should be wire-compatible.
• Changes to _vt tables and RPCs need to be backward compatible.
• RPC changes should be compatible with vitess-operator
• If a flag is removed, then it should also be removed from vitess-operator and arewefastyet, if used there.
• vtctl command output order should be stable and awk-able.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.22%. Comparing base (f118ba2) to head (c95691f).
Report is 202 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16113      +/-   ##
==========================================
- Coverage   68.40%   68.22%   -0.19%     
==========================================
  Files        1556     1543      -13     
  Lines      195121   197587    +2466     
==========================================
+ Hits       133479   134796    +1317     
- Misses      61642    62791    +1149     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.