Re: optimizer hints in Pig
In general I think optimizer hints fit well with Pig's approach to data processing, as expressed in our philosophic statement that Pigs are domestic animals (see http://hadoop.apache.org/pig/ philosophy.html ). At least in the examples you give, I don't see 'with' as binding. The user is giving Pig information; it can choose how to use it, or to not use it all. I would like 'using' to continue to be binding as in that case the user is explicitly telling Pig to do something in a particular way. Alan. On Nov 14, 2009, at 2:07 PM, Ashutosh Chauhan wrote: 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=1559955type=pdf
optimizer hints in Pig
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=1559955type=pdf
Re: optimizer hints in Pig
This should be interesting to pursue. For non-trivial plans, it can be used to model how join's are to be optimized for example - instead of having users specify it, infer based on the hints from various stages. Similarly, an oft-repeated request is making pig infer the value of PARALLEL - which can also be influenced by this : a- load, filter1, project b- load, filter2, project, filter3. join a, b. Now we can estimate 'sizes' of a and b based on input and arrive at things like : reducers to be used for a, b ; what kind of joint to use (traditional, fragment replicate, etc), and so on. This should be interesting if it scales to slightly more complex scripts. The example generator gets into some basic aspects of this iirc - though not from a costing function point of view (atleast I remember discussing it with Shubham). Regards, Mridul Ashutosh Chauhan wrote: 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=1559955type=pdf