Add a method to check if logger is enabled based on severity?

[ThomsonTan]

In the current log API in opentelemetry-cpp, like EmitLogRecord below, LogRecord is created and passed to processors directly. minSeverity should be checked in the beginning to avoid all the heavy operations like log information calculation and log record creation. I think the best thing is we provide a wrapper function like logger::Enabled(severity) as a fast pre-check before producing any log data. .NET has something similar here.

https://github.com/open-telemetry/opentelemetry-cpp/blob/main/api/include/opentelemetry/logs/logger.h#L163

[owent]

Good point, many log library have functions to set and get log level, though it seems not be a part of specification.

[lalitb]

The otel specification doesn't provide any logging API which can be directly called through instrumentation library, as indicated here -

Note: this document defines a log backend API. The API is not intended to be called by application developers directly. It is provided for logging library authors to build [Appenders](https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/logs/api.md#how-to-create-log4j-style-appender), which use this API to bridge between existing logging libraries and the OpenTelemetry log data model.

So it ONLY defines log backend API and log SDK. Most of the languages have their own native logging APIs, and the otel log backend API enables these languages SIGs to develop Appenders to connect their native APIs to logging SDK.

<native-api> --> <appender using log backend API> --> logging SDK -> otel exporters

The get/set level are generally part of these language provided native-api. E.g., for python:

import logging
logging.basicConfig(filename='example.log', encoding='utf-8', level=logging.DEBUG)

This is probably the reason why we don't have any get and set log levels as part of this log backend API.

In case of C++ language, the application developers may be using an existing logging framework (say) spdlog or log4cxx. Someone needs to then develop appenders using log backend API to emit logs through OpenTelemetry provided exporters:

<spdlog/log4cxx> --> <appender using log backend API> --> logging SDK -> otel-exporters

If we want to support configuring log-level as part of otel-cpp, we can provide a similar convenience library/wrapper at api level with basic functions to emit logs, set/get level, something like:

otel::init_log() -> configures log provider and logger
otel::set_log_level(severity) - Set log level
otel::log() --> Check log level, create logRecord and use Logger::Emit()

If we plan to provide this convenience library/wrapper, this is something can be done once our logs backend API and log SDK are stable.

I think it would be good idea to provide this convenience library/wrapper once our logs backend API and log SDK are stable.

[ssams]

I've seen that as of #2094 (comment) there is an (internal) SetMinimumSeverity on the logger, which is according to the comment supposed to be configurable via the SDK. However, I currently don't see any functionality on the SDK LoggerProviderFactory / LoggerProvider which would allow to influence this - am I overlooking something or is still missing / in progress?