data:type:log:log

Table of Contents

About

A log is a text file with:

a timed list of message (activities)
that an application has performed

Example

execution/request log:
- web server:
  - web log (Apache - Web Log (Activity Log) - that stores the Http request
  - error
- cron
connection log:
- ftp
- ssh (/var/log/secure)

Usage

Debugging: Inserting log statements into code is a low-tech method for debugging it.
Monitoring
For data log as a fault tolerance purposes (Undo/Redo) in a database. See Data Management - (Transaction|Request|Commit|Redo) Log
Analytics: Because it's hard to know in advance what data might be useful to analyze, a common approach is to log it all and sort through it later.
Distributed Services: Distributed - Tracing
Security: The log activity can be monitored in order to track suspicious activity (example ssh login for instance)

Structure

The basic structure of a log entry is:

a timestamp
a text message
optional extra attributes

Server Application

Because:

they are point in time event registration, they fall in the category of time serie
they stores text message, the log platorms are specialized search engine.

Management

Creator

The creation of log is done via a library.

Example of Java Logger Library

Format

See What are the known formats for Log files?

Processing

When the log file are becoming too big, you need to:

collect them
or rotate them

(Standard|Specification)

Severity / Level

Generally, a level value is present in a log line that specifies the order of severity. See Logging - Level

Documentation / Reference