Add structured logging with slog

[mhamza15]

Description

Adds support for JSON structured logging with slog. To enable, pass --log-structured and optionally a --log-level debug|info|warn|error (default info). glog is still the default unless slog is explicitly enabled with the flags.

We still use a global logging package go/vt/log to make the migration easier. In the future, each component should be passed in a logger.

The global functions in the log package now check if structured logging is enabled. If so, passes the message to slog. If not, passes it to glog as normal.

Call sites were migrated using ast-grep as so:

• Info(...) => Info(fmt.Sprint(...))
• Infof(...) => Info(fmt.Sprintf(...))
• ...and so on for other levels and Depth variants.

Call sites are now free to incrementally add additional attributes to the message.

Example JSON output:

$ ./bin/vttablet --log-structured
{"time":"2026-01-22T16:13:49.136782-05:00","level":"INFO","source":{"function":"vitess.io/vitess/go/vt/servenv.Init","file":"vitess.io/vitess/go/vt/servenv/servenv_unix.go","line":58},"msg":"Version: 24.0.0-SNAPSHOT (Git revision bba55101eeb6be4ce10914eec14daee3008189c7 branch 'structured-logging-slog') built on Thu Jan 22 15:59:46 EST 2026 by [email protected] using go1.25.6 darwin/arm64"}
{"time":"2026-01-22T16:13:49.136913-05:00","level":"ERROR","source":{"function":"vitess.io/vitess/go/vt/topo.Open","file":"vitess.io/vitess/go/vt/topo/server.go","line":261},"msg":"topo-global-server-address must be configured"}

Benchmark quick links:

• The previous PR using zerolog, zerolog disabled: https://benchmark.vitess.io/compare?old=main&new=e8e6076ba6c8dc88aab64e642435327a5a4ab9e9
• The previous PR using zerolog, zerolog enabled: https://benchmark.vitess.io/compare?old=main&new=549fe7f84e16e8d2b3a20b6e4c0fa61ffb6dad32
• This PR, slog disabled: https://benchmark.vitess.io/compare?old=main&new=6152c8df55df6a0299f8439828a3711ca432aa2c
• This PR, slog enabled: https://benchmark.vitess.io/compare?old=main&new=67978902be5d1f66ab8f6e1d4a795228bda8b6fa

Related Issue(s)

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 was added or is not required

Deployment Notes

AI Disclosure

[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.
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• There should be a comment at the top of each new or modified test to explain what the test does.

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• 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.

[vitess-bot]

Hello! 👋

This Pull Request is now handled by arewefastyet. The current HEAD and future commits will be benchmarked.

You can find the performance comparison on the arewefastyet website.

[codecov]

Codecov Report

❌ Patch coverage is 32.23413% with 822 lines in your changes missing coverage. Please review.
✅ Project coverage is 69.84%. Comparing base (ce8a335) to head (b14f15a).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
go/vt/mysqlctl/mysqld.go	8.97%	71 Missing ⚠️
go/vt/tlstest/tlstest.go	5.40%	70 Missing ⚠️
go/vt/log/log.go	63.04%	34 Missing ⚠️
go/vt/log/prefix.go	0.00%	31 Missing ⚠️
go/cmd/vtbackup/cli/vtbackup.go	0.00%	29 Missing ⚠️
go/mysql/conn.go	21.87%	25 Missing ⚠️
go/stats/statsd/statsd.go	0.00%	21 Missing ⚠️
go/cmd/vtcombo/cli/vschema_watcher.go	0.00%	19 Missing ⚠️
go/vt/binlog/binlogplayer/binlog_player.go	24.00%	19 Missing ⚠️
go/vt/servenv/servenv.go	26.08%	17 Missing ⚠️
... and 151 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #19203      +/-   ##
==========================================
- Coverage   69.88%   69.84%   -0.04%     
==========================================
  Files        1611     1613       +2     
  Lines      215944   216158     +214     
==========================================
+ Hits       150919   150985      +66     
- Misses      65025    65173     +148     

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