Make log level checks lock-free via permanent loggers.

[dmkozh]

Description

Make log level checks lock-free via permanent loggers.

Every CLOG_* invocation fetches its respective logger instance in order to check if we should log this line, and the getter used to be guarded by a recursive mutex lock. So we kept serializing every disabled log statement, which hindered parallelization for the code paths with frequent trace/debug logs.

Now each partition has a single permanent logger, created on first use and never destroyed or replaced (logging rotations/reconfigurations now are done at the sink level, instead of the logger level). Additionally, we avoid a shared ptr copy on every logger access, as we now we can just safely return a non-owning pointer to it.

The logging level checks per logger still have to be thread-safe, as the level may be changed in the middle of the app lifetime. We remove SPDLOG_NO_ATOMIC_LEVELS to achieve that, which simply uses very fast relaxed atomic checks.

This doesn't have too large impact right now (~-3ms on the local benchmarks), but it will become more meaningful as we land more apply path parallelization.

Checklist

• Reviewed the contributing document
• Rebased on top of master (no merge commits)
• Ran clang-format v8.0.0 (via make format or the Visual Studio extension)
• Compiles
• Ran all tests
• If change impacts performance, include supporting evidence per the performance document

[Copilot]

Pull request overview

Makes disabled log-level checks lock-free by retaining permanent logger instances and reconfiguring their sinks.

Changes:

• Adds permanent per-partition loggers with mutable distribution sinks.
• Returns non-owning logger pointers to avoid shared-pointer copies.
• Enables atomic runtime log-level updates.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/util/SpdlogTweaks.h	Enables atomic logger levels.
src/util/Logging.h	Documents permanent loggers and updates getter APIs.
src/util/Logging.cpp	Implements permanent loggers and sink reconfiguration.

[graydon]

LGTM