feat(logging): add CerrLogger std::cerr backend (3/6)#724
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feat(logging): add CerrLogger std::cerr backend (3/6)#724kamcheungting-db wants to merge 4 commits into
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Re-add spdlog as a build dependency to serve as the foundation for the logging system. Adapted to current structure: spdlog joins the core iceberg lib interface lists (roaring has since moved to iceberg_data). Co-authored-by: Isaac
This is the first of six small PRs that together add a logging system to iceberg-cpp. It introduces LogLevel, the severity scale everything else builds on: trace, debug, info, warn, error, critical, fatal, plus an `off` sentinel for turning logging off entirely. Levels are ordered from most to least verbose, so deciding whether something should be logged is a plain `level >= threshold` comparison. Two helpers come with it: ToString to print a level, and LogLevelFromString to parse one (case-insensitive, returning a Result for unrecognized input). Both follow the same shape as CounterUnit in metrics/counter.h. There is no implementation behind the header yet, so this PR only adds the header, wires the new src/iceberg/logging directory into the build, and adds a test covering the round-trip, ordering, and parsing. Co-authored-by: Isaac
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Second of the logging stack. This defines what a logger is and where the rest of the code finds one, with no concrete backend yet. Logger is a small abstract interface: ShouldLog to test a level, Log to emit an already-formatted record, SetLevel/level, Flush, and a shared no-op instance. Records are passed as LogMessage, which owns its formatted text (so a sink may safely hold onto it) and carries the source location plus a reserved slot for structured key/values we may add later. The interface spells out two rules for implementations: never call back into logging from inside Log/Flush, and keep level() a true lower bound for ShouldLog. There is also one default logger per process, designed to be cheap to reach on the logging path: a lock-free atomic level check drops disabled messages outright, and when a message does need logging the current logger comes from a thread-local cache that only refreshes when the default actually changes, so the steady state has no lock or reference-count traffic. SetDefaultLogger and SetDefaultLevel swap it safely under a mutex. The seed default is the no-op logger; CerrLogger and the spdlog backend arrive in later PRs. Also adds the build-generated, .cc-only config header used later to pick the backend, and tests for the interface and the default-logger lifecycle. Co-authored-by: Isaac
Third of the logging stack. This is the first concrete backend, and the default sink when spdlog is not compiled in. CerrLogger writes one line per record to std::cerr, for example: 2026-06-10T18:06:17.518Z error [295021] table.cc:42] opened snapshot 7 a UTC ISO-8601 timestamp with millisecond precision, the level, the OS thread id, the source file:line, then the message. The level threshold is a lock-free atomic, and a mutex guards each whole-line write so messages from different threads never interleave. Log and Flush wrap their work in try/catch so a logging call never throws, honoring the interface's noexcept contract. Being pure standard library, it is always compiled and becomes the seed default logger, replacing the no-op placeholder from the previous PR. Adds tests for the line format, level filtering, and concurrent writes. Co-authored-by: Isaac
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What
Third of the logging stack.
First concrete backend and the default sink when spdlog isn't compiled in. Writes one line per record to std::cerr — 2026-06-10T18:06:17.518Z error [295021] table.cc:42] msg (UTC ISO-8601 ms timestamp, level, OS thread id, file:line, message).
Level threshold is a lock-free atomic; a mutex guards each whole-line write so concurrent records don't interleave; Log/Flush swallow exceptions to uphold the noexcept contract. Becomes the seed default, replacing the no-op placeholder.
Testing
compiled and run with clang++ -std=c++23 -stdlib=libc++ (clang 18) — line format, level filtering, and a 6-thread × 40-line no-interleave test all pass.