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The "Hive/LanguageManual/DDL/BucketedTables" page has been changed by ZhengShao. http://wiki.apache.org/hadoop/Hive/LanguageManual/DDL/BucketedTables?action=diff&rev1=6&rev2=7 -------------------------------------------------- set mapred.reduce.tasks = 256; FROM ( FROM user_info u - SELECT CAST(userid AS BIGINT) AS userid_bigint, firstname, lastname + SELECT CAST(userid AS BIGINT) % 256 AS bucket_id, userid, firstname, lastname WHERE d.ds='2009-02-25' - CLUSTER BY userid_bigint + CLUSTER BY bucket_id ) c INSERT OVERWRITE TABLE user_info_bucketed PARTITION (ds='2009-02-25') - SELECT userid_bigint, firstname, lastname; + SELECT userid, firstname, lastname; }}} Note that I’m clustering by the integer version of userid. This might otherwise cluster by userid as a STRING (depending on the type of userid in user_info), which uses a totally different hash. It's important for the hashing function to be of the correct data type, since otherwise we'll expect userids in bucket 1 to satisfy (big_hash(userid) mod 256 == 0), but instead we'll be getting (string_hash(userid) mod 256 == 0). It's also good form to have all of your tables use the same type (eg, BIGINT instead of STRING) since that way your sampling from multiple tables will give you the same userids, letting join efficiently sample and join.
