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10.4.5 Tuning the garbage collector

The GC settings are tuned for typical cases, so in general you do not need to change them. If you are considering tuning the GC, contact Lisp Support.

The main tools for seeing how the GC behaves are the macro extended-time and periodical calls to room.

In the output of (room) (or the more verbose (room t) ), the allocation in each generation is presented according to the allocation type, which may be useful to decide on possible tuning.

(extended-time forms ) outputs the time spent in garbage collection, whether automatic or called explicitly. The time is shown according to the maximum generation number that was collected and to whether it was a standard garbage collection (automatic and calls to gc-generation) or a marking garbage collection (calls to marking-gc).

In addition to room and extended-time, there are also the functions count-gen-num-allocation, gen-num-segments-fragmentation-state, and set-automatic-gc-callback. These function can be used to collect information about automatic garbage collection operations.

The profiler can also help determine whether the settings can be improved for your application. See The Profiler for details of that. Interface for tuning the GC

LispWorks User Guide and Reference Manual - 21 Dec 2011