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Miklos Gergely commented on HIVE-20536: --------------------------------------- [~ashutoshc] I've tested the function with multi-table insert statement, and it was working fine. I couldn't test it with MERGE, because AFAIK currently MERGE doesnt' support inserting into specified columns. Assume that t1 has 3 columns * a int * b int * c bigint default surrogate_key() In order to insert into t1 one should specify the columns like this: {noformat} INSERT INTO t1 (a, b) VALUES (1, 2);{noformat} The same thing can not be done using merge, specifiying (a, b) like this is not supported: {noformat} MERGE INTO t1 ... WHEN NOT MATCHED THEN INSERT (a, b) VALUES (t2.a, t2.b);{noformat} Inserting without specifying the columns result in an error message that there are less values than columns. I suggest to support this syntax. > Add Surrogate Keys function to Hive > ----------------------------------- > > Key: HIVE-20536 > URL: https://issues.apache.org/jira/browse/HIVE-20536 > Project: Hive > Issue Type: Task > Components: Hive > Reporter: Miklos Gergely > Assignee: Miklos Gergely > Priority: Major > Attachments: HIVE-20536.01.patch, HIVE-20536.02.patch, > HIVE-20536.03.patch, HIVE-20536.04.patch, HIVE-20536.05.patch > > > Surrogate keys is an ability to generate and use unique integers for each row > in a table. If we have that ability then in conjunction with default clause > we can get surrogate keys functionality. Consider following ddl: > create table t1 (a string, b bigint default unique_long()); > We already have default clause wherein you can specify a function to provide > values. So, what we need is udf which can generate unique longs for each row > across queries for a table. > Idea is to use write_id . This is a column in metastore table TXN_COMPONENTS > whose value is determined at compile time to be used during query execution. > Each query execution generates a new write_id. So, we can seed udf with this > value during compilation. > Then we statically allocate ranges for each task from which it can draw next > long. So, lets say 64-bit write_id we divy up such that last 24 bits belong > to original usage of it that is txns. Next 16 bits are used for task_attempts > and last 24 bits to generate new long for each row. This implies we can allow > 17M txns, 65K tasks and 17M rows in a task. If you hit any of those limits we > can fail the query. > Implementation wise: serialize write_id in initialize() of udf. Then during > execute() we find out what task_attempt current task is and use it along with > write_id() to get starting long and give a new value on each invocation of > execute(). > Here we are assuming write_id can be determined at compile time, which should > be the case but we need to figure out how to get handle to it. -- This message was sent by Atlassian JIRA (v7.6.3#76005)