[logback-dev] TurboFilters to transform events

[Ceki Gülcü]

Hello all,

At present time, a TurboFilter cannot modify the contents of an
event. This decision was made in order to avoid the cost of
constructing a LoggingEvent (about 20 nanoseconds) which would be
later tossed out by the logger-level filter. 20 ns is not much but in
absolute terms but considering that invoking the logger-level filter
costs 3ns, 20ns is quite a steep price to pay in relative terms on
every logger printing method invocation (for disabled logger
requests).

For the case where there are no turbo filters installed, performance
would remain quasi-identical. For the case with one or more turbo
filters installed, there would be an extra cost of 20ns. However,
since invoking even the most rudimentary turbo filter costs 40ns or
more, I think the 20ns overhead is well spent considering that it
would allow turbo filters to transform events.

Unfortunately, the TurboFilter interface would need to be modified
breaking compatibility with existing turbo filters.

Comments?

--
Ceki