flatten(lineitem) uses all the fields from lineitem, hence no pruning.
On Fri, Dec 2, 2011 at 6:42 PM, Jie Li <[email protected]> wrote: > Sure. The two lines in bold are just dropping out non-necessary fields. > Without them Pig would not project, especially for the table lineitem. > > lineitem = load '$input/lineitem' USING PigStorage('|') as > (l_orderkey:long, l_partkey:long, l_suppkey:long, l_linenumber:long, > l_quantity:double, l_extendedprice:double, l_discount:double, l_tax:double, > l_returnflag:chararray, l_linestatus:chararray, l_shipdate:chararray, > l_commitdate:chararray, l_receiptdate:chararray,l_shippingstruct:chararray, > l_shipmode:chararray, l_comment:chararray); > > part = load '$input/part' USING PigStorage('|') as (p_partkey:long, > p_name:chararray, p_mfgr:chararray, p_brand:chararray, p_type:chararray, > p_size:long, p_container:chararray, p_retailprice:double, > p_comment:chararray); > > *lineitem = foreach lineitem generate l_partkey, l_quantity, > l_extendedprice ;* > part = FILTER part BY p_brand == 'Brand#23' AND p_container == 'MED BOX'; > *part = foreach part generate p_partkey;* > > COG1 = COGROUP part by p_partkey, lineitem by l_partkey; > COG1 = filter COG1 by COUNT(part) > 0; > COG2 = FOREACH COG1 GENERATE COUNT(part) as count_part, FLATTEN(lineitem), > 0.2 * AVG(lineitem.l_quantity) as l_avg; > > COG3 = filter COG2 by l_quantity < l_avg; > COG = foreach COG3 generate (l_extendedprice * count_part) as l_sum; > > G1 = group COG ALL; > > result = foreach G1 generate SUM(COG.l_sum)/7.0; > > > > On Fri, Dec 2, 2011 at 9:16 PM, Dmitriy Ryaboy <[email protected]> wrote: > >> Can you provide a script that shows projection not happening? We've >> observed the opposite (and use that fact extensively) >> >> D >> >> On Fri, Dec 2, 2011 at 4:05 PM, Jie Li <[email protected]> wrote: >> > Hi all, >> > >> > We just figured out Pig 0.9.1 doesn't drop those non-necessary fields >> asap, >> > which really affects the performance. Though >> > >> http://ofps.oreilly.com/titles/9781449302641/load_and_store_funcs.html#loadfunc_loaderpushdownsaid >> > that "As part of its optimizations Pig analyzes Pig Latin scripts and >> > determines what fields in an input it needs at each step in the script. >> It >> > uses this information to aggressively drop fields it no longer needs." >> > >> > We also found that Pig casts the data into the types defined in the >> schema, >> > which is usually unnecessary, as most of them will be soon dropped. >> > >> > To work around these, we have to manually drop those fields and remove >> the >> > types in the schema, which are really not interesting. >> > >> > Jie >> >>
