Beyond Monolog, other packages provide advanced logging services. Apache log4php is another well-known logging solution, used (among others) by CMS Made Simple, SugarCRM, and vTiger CRM.

It is based on the famous log4j package from the Java world, and from uses of this package I have seen on customer sites, I feel that it carries a lot of useless baggage, and is - in my opinion - significantly less of a good match than Monolog for Drupal 8.

Monolog vs log4php : equivalences

There is some degree of equivalence between the Monolog and log4php components:

Purpose
Monolog
log4php
Notes
Log an event
Logger
Logger
Very similar
Store an event
Handler
Appender
both can be chained, group, control bubbling (Monolog) / filtering (log4php)
Format an event representation
Formatter
Layout
log4php layouts can format a group of events, Monolog formatters format an individual event
Massage event data
Processor
Renderer
Not so similar. Monolog processors will often add extra data, while log4php Renderers are typically used to format non-string events as strings.

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