semantic_logger

Improved logging for Ruby

http://github.com/ClarityServices/semantic_logger

Note:

As of SemanticLogger V2.0 the Rails logging is no longer automatically replaced when including SemanticLogger. Include the rails_semantic_logger gem to replace the Rails default logger with SemanticLogger

Overview

Semantic Logger takes logging in Ruby to a new level by adding several new capabilities to the commonly used Logging API:

Dynamic

Increase the log level at runtime for just one class
For example enable debug level logging for a single class (logging instance) while the program is running to get more detailed logging in production for just that class

Tagged Logging

Supply custom data to be added to every log entry within a block of code, including libraries and existing gems
Tagged logging is critical for any high traffic site so that one can narrow down log entries for a single call that is mixed in with log entries from hundreds of other log entries

High Performance

Logging is performed in a separate thread so as not to impact performance of running code

Customizable

Custom formatting by destination
Easy to "roll your own" destination (Appender). For example to log to Hadoop, Redis, etc..

Payload support

Aside from the regular log message, a hash payload can also be supplied with every log entry
Very powerful when logging to NOSQL destinations that allow queries against any data in the payload

Exceptions

Directly log exceptions
Semantic Logger standardizes the logging of exceptions with their backtraces to text destinations and writes the exception elements as a hash to NOSQL destinations

Drop-in Replacement

Simple drop-in replacement for the Ruby, or the Rails loggers
Supports current common logging interface
No changes to existing to code to use new logger ( other than replacing the logger )

Thread Aware

Includes the process and thread id information in every log entry
If running JRuby it will also include the name of the thread for every log entry

Trace Level

:trace is a new level common in other languages and is commonly used for logging trace level detail. It is intended for logging data at level below :debug.
:trace can be used for logging the actual data sent or received over the network that is rarely needed but is critical when things are not working as expected.
Since :trace can be enabled on a per class basis it can even be turned on in production to resolve what was actually sent to an external vendor

Multiple Destinations

Log to multiple destinations at the same time ( File and MongoDB, etc.. )
Each destination can also have its own log level. For example, only log :info and above to MongoDB, or :warn and above to a second log file

Benchmarking

The performance of any block of code can be measured and logged at the same time depending on the active log level

Semantic Capabilities

With Semantic Logger it is simple to mix-in additional semantic information with every log entry
The application or class name is automatically included for every log entry under a specific logging instance
Includes the duration of blocks of code
Any hash containing context specific information such as user_id or location information

Beyond Tagged Logging

Supply entire hash of custom data to be added to the payload of every log entry within a block of code, including libraries and existing gems

NOSQL Destinations

Every log entry is broken down into elements that NOSQL data stores can understand:

{
    "_id" : ObjectId("5034fa48e3f3fea945e83ef2"),
    "time" : ISODate("2012-08-22T15:27:04.409Z"),
    "host_name" : "release",
    "pid" : 16112,
    "thread_name" : "main",
    "name" : "UserLocator",
    "level" : "debug",
    "message" : "Fetch user information",
    "duration" : 12,
    "payload" : {
        "user" : "Jack",
        "zip_code" : 12345,
        "location" : "US"
    }
}

Thread Safe

Semantic Logger is completely thread safe and all methods can be called concurrently from any thread
Tagged logging keeps any tagging data on a per-thread basis to ensure that tags from different threads are not inter-mingled

Introduction

Semantic Logger is a Logger that supports logging of meta-data, along with text messages to multiple appenders

An appender is a Logging destination such as a File, MongoDB collection, etc.. Multiple Appenders can be active at the same time. All log entries are written to each appender.

Machines can understand the logged data without having to use complex Regular Expressions or other text parsing techniques

Semantic Logger, sits on top of existing logger implementations and can also be used as a drop in replacement for existing Ruby loggers. This allows the existing logging to be replaced immediately with the Semantic Logger Appenders, and over time the calls can be replaced with ones that contain the necessary meta-data.

Example of current calls:

logger.info("Queried users table in #{duration} ms, with a result code of #{result}")

For a machine to find all queries for table 'users' that took longer than 100 ms, would require using a regular expression just to extract the table name and duration, then apply the necessary logic. It also assumes that the text is not changed and that matches will not be found when another log entry has similar text output.

This can be changed over time to:

logger.info("Queried table",
  :duration => duration,
  :result   => result,
  :table    => "users",
  :action   => "query")

Using the MongoDB appender, we can easily find all queries for table 'users' that took longer than 100 ms:

db.logs.find({"payload.table":"users", "payload.action":"query", "payload.duration":{$gt:100} })

Since Semantic Logger can call existing Loggers, it does not force end-users to have to adopt a Semantic aware adapter. Although, such adapters create tremendous value in the problem monitoring and determination processes.

Logging API

Standard Logging methods

The Semantic Logger logging API supports the existing logging interface for the Rails and Ruby Loggers. For example:

logger.info("Hello World")

Or to query whether a specific log level is set

logger.info?

The following logging methods are available

trace(message, payload=nil, exception=nil, &block)
debug(message, payload=nil, exception=nil, &block)
info(message, payload=nil, exception=nil, &block)
warn(message, payload=nil, exception=nil, &block)
error(message, payload=nil, exception=nil, &block)
fatal(message, payload=nil, exception=nil, &block)

Parameters

message: The text message to log. Mandatory only if no block is supplied
payload: Optional, either a Ruby Exception object or a Hash
exception: Optional, Ruby Exception object. Allows both an exception and a payload to be logged
block: The optional block is executed only if the corresponding log level is active. Can be used to prevent unnecessary calculations of debug data in production.

Examples:

logger.debug("Calling Supplier")

logger.debug("Calling Supplier", :request => 'update', :user => 'Jack')

logger.debug { "A total of #{result.inject(0) {|sum, i| i+sum }} were processed" }

Exceptions

The Semantic Logger adds an optional parameter to the existing log methods so that a corresponding Exception can be logged in a standard way

begin
  # ... Code that can raise an exception
rescue Exception => exception
  logger.error("Oops external call failed", exception)
  # Re-raise or handle the exception
  raise exception
end

Payload

The Semantic Logger adds an extra parameter to the existing log methods so that additional payload can be logged, such as a Hash or a Ruby Exception object.

logger.info("Oops external call failed", :result => :failed, :reason_code => -10)

The additional payload is machine readable so that we don't have to write complex regular expressions so that a program can analyze log output. With the MongoDB appender the payload is written directly to MongoDB as part of the document and is therefore fully searchable

Benchmarking

Another common logging requirement is to measure the time it takes to execute a block of code based on the log level. For example:

Rails.logger.benchmark_info "Calling external interface" do
  # Code to call external service ...
end

The following output will be written to file:

2012-08-30 15:37:29.474 I [48308:ScriptThreadProcess: script/rails] (5.2ms) Rails -- Calling external interface

If an exception is raised during the block the exception is logged at the same log level as the benchmark along with the duration and message. The exception will flow through to the caller unchanged

The following benchmarking methods are available

benchmark_trace(message, params=nil, &block)
benchmark_debug(message, params=nil, &block)
benchmark_info(message, params=nil, &block)
benchmark_warn(message, params=nil, &block)
benchmark_error(message, params=nil, &block)
benchmark_fatal(message, params=nil, &block)

Parameters

message: The mandatory text message to log.
params: ``` :log_exception Control whether or how an exception thrown in the block is reported by Semantic Logger. Values: :full Log the exception class, message, and backtrace :partial Log the exception class and messag The backtrace will not be logged :off Any unhandled exception from the block will not be logged

:min_duration Only log if the block takes longer than this duration in ms Default: 0.0

:payload Optional, Hash payload

:exception Optional, Ruby Exception object to log along with the duration of the supplied block


### Logging levels

The following logging levels are available through Semantic Logger

    :trace, :debug, :info, :warn, :error, :fatal

The log levels are listed above in the order of precedence with the most detail to the least.
For example :debug would include :info, :warn, :error, :fatal levels but not :trace
And :fatal would only log :fatal error messages and nothing else

:unknown has been mapped to :fatal for Rails and Ruby Logger

:trace is a new level that is often used for tracing low level calls such
as the data sent or received to external web services. It is also commonly used
in the development environment for low level trace logging of methods calls etc.

If only the rails logger is being used, then :trace level calls will be logged
as debug calls only if the log level is set to trace

### Changing the Class name for Log Entries

When Semantic Logger is included in a Rails project it automatically replaces the
loggers for Rails, ActiveRecord::Base, ActionController::Base, and ActiveResource::Base
with wrappers that set their Class name. For example in semantic_logger/railtie.rb:

```ruby
ActiveRecord::Base.logger = SemanticLogger[ActiveRecord]

By replacing their loggers we now get the class name in the text logging output:

2012-08-30 15:24:13.439 D [47900:main] ActiveRecord --   SQL (12.0ms)  SELECT `schema_migrations`.`version` FROM `schema_migrations`

It is recommended to include a class specific logger for all major classes that will be logging using the SemanticLogger::Loggable mix-in. For Example:

require 'semantic_logger'

class ExternalSupplier
  # Lazy load logger class variable on first use
  include SemanticLogger::Loggable

  def call_supplier(amount, name)
    logger.debug "Calculating with amount", { :amount => amount, :name => name }

    # Measure and log on completion how long the call took to the external supplier
    logger.benchmark_info "Calling external interface" do
      # Code to call the external supplier ...
    end
  end
end

This will result in the log output identifying the log entry as from the ExternalSupplier class

2012-08-30 15:37:29.474 I [48308:ScriptThreadProcess: script/rails] (5.2ms) ExternalSupplier -- Calling external interface

Tagged Logging

Semantic Logger allows any Ruby or Rails program to also include tagged logging.

This means that any logging performed within a block, including any called libraries or gems to include the specified tag with every log entry.

Using Tagged logging is critical in any highly concurrent environment so that one can quickly find all related log entries across all levels of code, and even across threads

logger.tagged(tracking_number) do
  logger.debug("Hello World")
  # ...
end

Beyond Tagged Logging

Blocks of code can be tagged with not only values, but can be tagged with entire hashes of data. The additional hash of data will be merged into the payload of every log entry

For example every corresponding log entry could include a hash containing a user_id, name, region, zip_code, tracking_number, etc...

logger.with_payload(:user => 'Jack', :zip_code => 12345) do
  logger.debug("Hello World")
  # ...
end

Standalone SemanticLogger

When using SemanticLogger inside of Rails all we need to do is include the rails_semantic_logger gem and the default Rails logger will be replaced with Semantic Logger.

In a stand-alone or non-rails environment we can easily log to a file called 'development.log' as follows:

require 'semantic_logger'
SemanticLogger.add_appender('development.log')

logger = SemanticLogger['Example']
logger.info "Hello World"

By default it will only log :info and above, to log everything to the log file:

require 'semantic_logger'
SemanticLogger.default_level = :trace
SemanticLogger.add_appender('development.log')

logger = SemanticLogger['Example']
logger.info "Hello World"
logger.trace "Low level trace information"

By supplying multiple appenders Semantic Logger can write to multiple destinations at the same time. For example, log to a file and the screen:

require 'semantic_logger'
SemanticLogger.default_level = :trace
SemanticLogger.add_appender('development.log')
SemanticLogger.add_appender(STDOUT)

logger = SemanticLogger['Example']
logger.info "Hello World"
logger.trace "Low level trace information"

To reduce the log level of logging to STDOUT to just :info and above, add the log_level such as :info as the second parameter when adding the appender:

require 'semantic_logger'
SemanticLogger.default_level = :trace
SemanticLogger.add_appender('development.log')
SemanticLogger.add_appender(STDOUT, :info)

logger = SemanticLogger['Example']
logger.info "Hello World"
logger.trace "Low level trace information"

To log :debug and above to a log file, :error and above to $stderr, and :info and above to MongoDB:

require 'semantic_logger'
require 'mongo'

SemanticLogger.default_level = :debug
SemanticLogger.add_appender('development.log')
SemanticLogger.add_appender($stderr, :error)

mongo_appender = SemanticLogger::Appender::MongoDB.new(
  :db              => Mongodb::Connection.new['production_logging'],
  :collection_size => 25.gigabytes
)
SemanticLogger.add_appender(mongo_appender, :info)

logger = SemanticLogger['Example']
logger.info "Hello World"
logger.trace "Low level trace information"
logger.error "Oops an error occurred"
logger.info("Login time", :user => 'Mary', :duration => 230, :ip_address=>'192.168.0.1')

When starting out with Semantic Logger it can be useful to gain all the benefits of Semantic Logger and still continue to log to an existing logger:

require 'logger'
require 'semantic_logger'

# Built-in Ruby logger
log = Logger.new(STDOUT)
log.level = Logger::DEBUG

SemanticLogger.default_level = :debug
SemanticLogger.add_appender(log)

logger = SemanticLogger['Example']
logger.info "Hello World"
logger.debug("Login time", :user => 'Joe', :duration => 100, :ip_address=>'127.0.0.1')

It is recommended that every class or module have it's own logging instance. This can be achieved by including SemanticLogger::Loggable:

require 'semantic_logger'
SemanticLogger.default_level = :trace
SemanticLogger.add_appender('development.log')

class ExternalSupplier
  # Makes available a class and instance level logger
  #    ExternalSupplier.logger and ExternalSupplier#logger
  include SemanticLogger::Loggable

  # logger class method example
  def self.hostname=(hostname)
    logger.debug "Setting hostname to #{hostname}"
    @@hostname = hostname
  end

  # logger instance method example
  def call_supplier(amount, name)
    logger.debug "Calculating with amount", { :amount => amount, :name => name }

    # Measure and log on completion how long the call took to the external supplier
    logger.benchmark_info "Calling external interface" do
      # Code to call the external supplier ...
    end
  end
end

Logging to Syslog

Log to a local Syslog:

require 'semantic_logger'
SemanticLogger.default_level = :trace
SemanticLogger.add_appender(SemanticLogger::Appender::Syslog.new)

Log to a local file and to a remote Syslog server such as syslog-ng over TCP:

require 'semantic_logger'
SemanticLogger.default_level = :trace
SemanticLogger.add_appender('development.log')
SemanticLogger.add_appender(SemanticLogger::Appender::Syslog.new(:server => 'tcp://myloghost:514'))

Configuration

The Semantic Logger follows the principle where multiple appenders can be active at the same time. For example, this allows one to log to MongoDB and the Rails log file at the same time.

Rails Configuration

To automatically replace the Rails logger with Semantic Logger use the gem rails_semantic_logger

Log Struct

Internally all log messages are passed around in a Log Struct. In order to write your own custom formatter or log appender it is necessary to understand the fields:

Log = Struct.new(:level, :thread_name, :name, :message, :payload, :time, :duration, :tags, :level_index)

level [Symbol]

Log level of the supplied log call
:trace, :debug, :info, :warn, :error, :fatal

thread_name [String]

Name or id of the thread in which the logging call was called

name [String]

Class name supplied to the logging instance

message [String]

Text message to be logged

payload [Hash|Exception]

Optional Hash or Ruby Exception object to be logged

time [Time]

The time at which the log entry was created

duration [Float]

The time taken in milli-seconds to complete a benchmark call

tags [Array]

Any tags active on the thread when the log call was made

level_index [Integer]

Internal use only. Index of the log level

Mixing Logging Levels

It is sometimes useful to log a subset of the log messages to a separate file or appender. For example, log :error and :fatal level messages to a special error file.

Below is a stand-alone example that better shows this behavior:

require 'semantic_logger'

# Set default log level for new logger instances
SemanticLogger.default_level = :info

# Log all warning messages and above to warnings.log
SemanticLogger.add_appender('log/warnings.log', :warn)

# Log all trace messages and above to trace.log
SemanticLogger.add_appender('log/trace.log', :trace)

logger = SemanticLogger['MyClass']
logger.level = :trace
logger.trace "This is a trace message"
logger.info "This is an info message"
logger.warn "This is a warning message"

The output is as follows:

==> trace.log <==
2013-08-02 14:15:56.733532 T [35669:70176909690580] MyClass -- This is a trace message
2013-08-02 14:15:56.734273 I [35669:70176909690580] MyClass -- This is an info message
2013-08-02 14:15:56.735273 W [35669:70176909690580] MyClass -- This is a warning message

==> warnings.log <==
2013-08-02 14:15:56.735273 W [35669:70176909690580] MyClass -- This is a warning message

Custom Formatters

The formatting for each appender can be replaced with custom code. To replace the existing formatter supply a block of code when creating the appender.

Example: Formatter that just returns the Log Struct

require 'semantic_logger'

SemanticLogger.default_level = :trace

SemanticLogger.add_appender(STDOUT) do |log|
 # This formatter just returns the log struct as a string
  log.inspect
end

logger = SemanticLogger['Hello']
logger.info "Hello World"

Output:

#<struct SemanticLogger::Base::Log level=:info, thread_name=70167090649820, name="Hello", message="Hello World", payload=nil, time=2012-10-24 10:09:33 -0400, duration=nil, tags=nil, level_index=2>

Example: Replace the default log file formatter

require 'semantic_logger'
SemanticLogger.default_level = :trace

SemanticLogger.add_appender('development.log') do |log|
tags = log.tags.collect { |tag| "[#{tag}]" }.join(" ") + " " if log.tags && (log.tags.size > 0)

message = log.message.to_s
message << " -- " << log.payload.inspect if log.payload
message << " -- " << "#{log.exception.class}: #{log.exception.message}\n#{(log.exception.backtrace || []).join("\n")}" if log.exception

duration_str = log.duration ? "(#{'%.1f' % log.duration}ms) " : ''

"#{SemanticLogger::Appender::Base.formatted_time(log.time)} #{log.level.to_s[0..0].upcase} [#{$$}:#{log.thread_name}] #{tags}#{duration_str}#{log.name} -- #{message}"
end

Example: Replace the default MongoDB formatter

# Log to MongoDB and supply a custom document formatter
mongodb_appender = SemanticLogger::Appender::MongoDB.new(
  :db              => Cache::Work.db,
  :collection_size => 25.gigabytes
) do |log|
    # Return a document (Hash) of the data to be saved to MongoDB
    document = {
      :time        => log.time,
      :host_name   => SemanticLogger::Appender::MongoDB.host_name,
      :pid         => $PID,
      :thread_name => log.thread_name,
      :name        => log.name,
      :level       => log.level,
      :level_index => log.level_index,
    }
    document[:application] = 'MyApplication'
    document[:message]     = SemanticLogger::Appender::MongoDB.strip_colorizing(log.message) if log.message
    document[:duration]    = log.duration if log.duration
    document[:tags]        = log.tags if log.tags && (log.tags.size > 0)
    document[:payload]     = log.payload if log.payload
    document[:exception]   = {
      :name        => log.exception.class.name,
      :message     => log.exception.message,
      :stack_trace => log.exception.backtrace
    } if log.exception
    document
end
SemanticLogger.add_appender(mongodb_appender)

Performance

The traditional logging implementations write their log information to file in the same thread of execution as the program itself. This means that for every log entry the program has to wait for the data to be written.

With Semantic Logger it uses a dedicated thread for logging so that writing to the log file or other appenders does not hold up program execution.

Also, since the logging is in this separate thread there is no impact to program execution if we decided to add another appender. For example, log to both a file and a MongoDB collection.

Log Rotation

Since the log file is not re-opened with every call, when the log file needs to be rotated, use a copy-truncate operation over deleting the file.

Why Semantic logging?

Just as there is the initiative to add Semantic information to data on the web so that computers can directly understand the content without having to resort to complex regular expressions or machine learning techniques, it is important to be able to do the same with log files or data.

Semantic Logger allows every log entry to have not only a message, but a payload that can be written to a file or a NOSQL destination.

Once the logging data is in the NOSQL data store it can be queried quickly and efficiently. Some SQL data stores also allow complex data types that could be used for storing and querying the logging data

Architecture & Performance

In order to ensure that logging does not hinder the performance of the application all log entries are written to thread-safe Queue. A separate thread is responsible for writing the log entries to each of the appenders.

In this way formatting and disk or network write delays will not affect the performance of the application. Also adding more than one appender does not affect the runtime performance of the application.

The logging thread is automatically started on initialization. When the program terminates it will call flush on each of the appenders.

Calling SemanticLogger::Logger#flush will wait until all outstanding log messages have been written and flushed to their respective appenders before returning.

Write your own Appender

To write your own appender it should meet the following requirements:

Inherit from SemanticLogger::Base
In the initializer connect to the resource being logged to
Implement #log(log) which needs to write to the relevant resource
Implement #flush if the resource can be flushed
Write a test for the new appender

The #log method takes the log struct as a parameter which is described above.

Basic outline for an Appender:

require 'semantic_logger'

class SimpleAppender < SemanticLogger::Appender::Base
  def initialize(level=nil, &block)
    # Set the log level and formatter if supplied
    super(level, &block)
  end

  # Display the log struct and the text formatted output
  def log(log)
    p log
    puts formatter.call(log)
  end

  # Optional
  def flush
    puts "Flush :)"
  end
end

Sample program calling the above appender:

SemanticLogger.default_level = :trace
# Log to file dev.log
SemanticLogger.add_appender('dev.log')
# Also log the above sample appender
SemanticLogger.add_appender(SimpleAppender.new)

logger = SemanticLogger['Hello']
logger.info "Hello World"

Look at the existing appenders for good examples

To have your appender included in the standard list of appenders follow the fork instructions below. Very Important: New appenders will not be accepted without complete working tests. See the MongoDB Appender Test for an example.

Dependencies

Ruby MRI 1.8.7, 1.9.3 (or above) Or, JRuby 1.6.3 (or above)
Optional: To log to MongoDB, Mongo Ruby Driver 1.5.2 or above

Install

gem install semantic_logger

To log to MongoDB, it also needs the Ruby Mongo Driver

gem install mongo

Future

Add support for a configuration file that can set log level by class name
Configuration file to support adding appenders
Based on end-user demand add appenders for: Syslog, hadoop, redis, etc..

Author

Reid Morrison :: [email protected] :: @reidmorrison

Contributors

Marc Bellingrath :: [email protected]

License

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

semantic_logger

Note:

Overview

Introduction

Logging API

Standard Logging methods

Exceptions

Payload

Benchmarking

Tagged Logging

Beyond Tagged Logging

Standalone SemanticLogger

Logging to Syslog

Configuration

Rails Configuration

Log Struct

Mixing Logging Levels

Custom Formatters

Performance

Log Rotation

Why Semantic logging?

Architecture & Performance

Write your own Appender

Dependencies

Install

Future

Meta

Author

Contributors

License