Apache Wiki
Thu, 24 Apr 2008 17:57:52 -0700
Dear Wiki user, You have subscribed to a wiki page or wiki category on "Pig Wiki" for change notification. The following page has been changed by ChrisOlston: http://wiki.apache.org/pig/PigOptimizationWishList ------------------------------------------------------------------------------ * look for ways to do multiple group/cogroup/join operations in a single map-reduce job --- this would occur if the keys share a common prefix. Example: group by userid+hour, then count, then group by userid, then take max --- can be done in one map-reduce job with userid as the reduce key. * choose a join strategy (symmetric hashing, fragment-and-replicate, ...); can probably make a reasonable choice based on file sizes [but first, we have to implement various join strategies in the execution layer -- currently pig only supports symmetric hashing] + * choose a CROSS strategy ((1) n-by-m grid, as currently implemented; or (2) n-by-1 which is better in the case of crossing a large table with a very small table, which can be implemented as map-only) [a common example of crossing a large table with a small one is when you have to normalize all records of Table A by dividing by a scalar S -- you can do this by crossing Table A with a Table B containing a single record that holds S] === Probably won't get there, and may not even want to go there ===