Find now has a rudimentary cost-based optimiser in findutils-4.3.1 and later releases; you can see it in the current CVS code. It is not turned on by default.
The cost-based optimiser has an idea of the basic cost of each test (i.e. that -name is very cheap while -size is more expensive). It re-orders tests bearing in mind the cost of each test and its likely success. Predicates with side effects (for example -delete or -exec) are not reordered. The optimiser is not yet enabled by default, but the new option -O controls the query optimisation level. To see this in action, try find -D opt -O3 . -type f -o -type c -o -size 555 -name Z and compare the optimised query with: find -D opt -O3 . -size 555 -o -type c -o -type f -name Z and find -D opt . -size 555 -o -type c -o -type f -name Z Over time, as optimisations are proven to be robust and correct, they will be moved to lower optimisation levels. Some optimisations have always been performed by find (for example -name is always done early if possible). If these optimisations prove to be ineffective or it turns out that the speed gain is negligible compared to the complexity, the cost-based optimiser may be removed again. However, the current complexity is artificially inflated to a degree since the current code needs to preserve the traditional behaviour when the -O option is not used. Feedback would be appreciated. James. _______________________________________________ Bug-findutils mailing list Bug-findutils@gnu.org http://lists.gnu.org/mailman/listinfo/bug-findutils
