Hi All, We would like to know what Pig devs feel about optimizer hints. Traditionally, optimizer hints have been received with mixed reactions in RDBMS world. Oracle provides lots of knobs[1][2] to turn and tune, while postgres[3][4] have tried to stay away from them. Mysql have few of them (e.g., straight_join). Surajit Chaudhary [5] (Microsoft) is making case in favor of them. More specifically, I am talking of hints like following
a = filter 'mydata' by myudf ($1) with "selectivity 0.5"; // This is letting user to tell Pig that myudf filters out nearly half of tuples of 'mydata'. c = join a by $0, b by $0 with "selectivity a.$0 = b.$0, 0.1"; // This is letting user to tell Pig that only 10% of keys in a will match with those in b. Exact syntax isn't important it could be adapted. But, question is does it seem to be a useful enough idea to be added in Pig Latin. Pig's case is slightly different from other sql engines in that while other systems treats them as "hints" and thus are free to ignore them Pig treats hints as commands in a sense that it will fail even if it can figure out that hint will result in failure of query. Perhaps, Pig can interpret "using" as command and "with" as hint. Thoughts? Ashutosh [1] http://www.dba-oracle.com/art_otn_cbo_p7.htm [2] http://www.dba-oracle.com/oracle11g/oracle_11g_extended_optimizer_statistics.htm [3] http://archives.postgresql.org/pgsql-hackers/2006-10/msg00663.php [4] http://archives.postgresql.org/pgsql-hackers/2006-08/msg00506.php [5] portal.acm.org/ft_gateway.cfm?id=1559955&type=pdf
