[jira] Commented: (HIVE-1994) Support new annotation @UDFType(stateful = true)
[ https://issues.apache.org/jira/browse/HIVE-1994?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanelfocusedCommentId=12998991#comment-12998991 ] Carl Steinbach commented on HIVE-1994: -- +1. Will commit if tests pass. Support new annotation @UDFType(stateful = true) Key: HIVE-1994 URL: https://issues.apache.org/jira/browse/HIVE-1994 Project: Hive Issue Type: Improvement Components: Query Processor, UDF Reporter: John Sichi Assignee: John Sichi Fix For: 0.8.0 Attachments: HIVE-1994.0.patch, HIVE-1994.1.patch, HIVE-1994.2.patch, HIVE-1994.3.patch Because Hive does not yet support window functions from SQL/OLAP, people have started hacking around it by writing stateful UDF's for things like cumulative sum. An example is row_sequence in contrib. To clearly mark these, I think we should add a new annotation (with separate semantics from the existing deterministic annotation). I'm proposing the name stateful for lack of a better idea, but I'm open to suggestions. The semantics are as follows: * A stateful UDF can only be used in the SELECT list, not in other clauses such as WHERE/ON/ORDER/GROUP * When a stateful UDF is present in a query, there's an implication that its SELECT needs to be treated as similar to TRANSFORM, i.e. when there's DISTRIBUTE/CLUSTER/SORT clause, then run inside the corresponding reducer to make sure that the results are as expected. For the first one, an example of why we need this is AND/OR short-circuiting; we don't want these optimizations to cause the invocation to be skipped in a confusing way, so we should just ban it outright (which is what SQL/OLAP does for window functions). For the second one, I'm not entirely certain about the details since some of it is lost in the mists in Hive prehistory, but at least if we have the annotation, we'll be able to preserve backwards compatibility as we start adding new cost-based optimizations which might otherwise break it. A specific example would be inserting a materialization step (e.g. for global query optimization) in between the DISTRIBUTE/CLUSTER/SORT and the outer SELECT containing the stateful UDF invocation; this could be a problem if the mappers in the second job subdivides the buckets generated by the first job. So we wouldn't do anything immediately, but the presence of the annotation will help us going forward. -- This message is automatically generated by JIRA. - For more information on JIRA, see: http://www.atlassian.com/software/jira
[jira] Commented: (HIVE-1994) Support new annotation @UDFType(stateful = true)
[ https://issues.apache.org/jira/browse/HIVE-1994?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanelfocusedCommentId=12998171#comment-12998171 ] John Sichi commented on HIVE-1994: -- Note that for CASE expressions, we *always* want short circuiting, otherwise it's impossible to do something like case when x 0 then sqrt(-x) else sqrt(x) end (to avoid trying to take the square root of a negative number). So if we detect a stateful UDF inside of a CASE expression, we'll throw an exception. Support new annotation @UDFType(stateful = true) Key: HIVE-1994 URL: https://issues.apache.org/jira/browse/HIVE-1994 Project: Hive Issue Type: Improvement Components: Query Processor, UDF Reporter: John Sichi Assignee: John Sichi Attachments: HIVE-1994.0.patch Because Hive does not yet support window functions from SQL/OLAP, people have started hacking around it by writing stateful UDF's for things like cumulative sum. An example is row_sequence in contrib. To clearly mark these, I think we should add a new annotation (with separate semantics from the existing deterministic annotation). I'm proposing the name stateful for lack of a better idea, but I'm open to suggestions. The semantics are as follows: * A stateful UDF can only be used in the SELECT list, not in other clauses such as WHERE/ON/ORDER/GROUP * When a stateful UDF is present in a query, there's an implication that its SELECT needs to be treated as similar to TRANSFORM, i.e. when there's DISTRIBUTE/CLUSTER/SORT clause, then run inside the corresponding reducer to make sure that the results are as expected. For the first one, an example of why we need this is AND/OR short-circuiting; we don't want these optimizations to cause the invocation to be skipped in a confusing way, so we should just ban it outright (which is what SQL/OLAP does for window functions). For the second one, I'm not entirely certain about the details since some of it is lost in the mists in Hive prehistory, but at least if we have the annotation, we'll be able to preserve backwards compatibility as we start adding new cost-based optimizations which might otherwise break it. A specific example would be inserting a materialization step (e.g. for global query optimization) in between the DISTRIBUTE/CLUSTER/SORT and the outer SELECT containing the stateful UDF invocation; this could be a problem if the mappers in the second job subdivides the buckets generated by the first job. So we wouldn't do anything immediately, but the presence of the annotation will help us going forward. -- This message is automatically generated by JIRA. - For more information on JIRA, see: http://www.atlassian.com/software/jira
[jira] Commented: (HIVE-1994) Support new annotation @UDFType(stateful = true)
[ https://issues.apache.org/jira/browse/HIVE-1994?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanelfocusedCommentId=12998197#comment-12998197 ] John Sichi commented on HIVE-1994: -- HIVE-1994.1.patch addresses short-circuiting. I'm running it through tests now. Support new annotation @UDFType(stateful = true) Key: HIVE-1994 URL: https://issues.apache.org/jira/browse/HIVE-1994 Project: Hive Issue Type: Improvement Components: Query Processor, UDF Reporter: John Sichi Assignee: John Sichi Attachments: HIVE-1994.0.patch, HIVE-1994.1.patch Because Hive does not yet support window functions from SQL/OLAP, people have started hacking around it by writing stateful UDF's for things like cumulative sum. An example is row_sequence in contrib. To clearly mark these, I think we should add a new annotation (with separate semantics from the existing deterministic annotation). I'm proposing the name stateful for lack of a better idea, but I'm open to suggestions. The semantics are as follows: * A stateful UDF can only be used in the SELECT list, not in other clauses such as WHERE/ON/ORDER/GROUP * When a stateful UDF is present in a query, there's an implication that its SELECT needs to be treated as similar to TRANSFORM, i.e. when there's DISTRIBUTE/CLUSTER/SORT clause, then run inside the corresponding reducer to make sure that the results are as expected. For the first one, an example of why we need this is AND/OR short-circuiting; we don't want these optimizations to cause the invocation to be skipped in a confusing way, so we should just ban it outright (which is what SQL/OLAP does for window functions). For the second one, I'm not entirely certain about the details since some of it is lost in the mists in Hive prehistory, but at least if we have the annotation, we'll be able to preserve backwards compatibility as we start adding new cost-based optimizations which might otherwise break it. A specific example would be inserting a materialization step (e.g. for global query optimization) in between the DISTRIBUTE/CLUSTER/SORT and the outer SELECT containing the stateful UDF invocation; this could be a problem if the mappers in the second job subdivides the buckets generated by the first job. So we wouldn't do anything immediately, but the presence of the annotation will help us going forward. -- This message is automatically generated by JIRA. - For more information on JIRA, see: http://www.atlassian.com/software/jira
[jira] Commented: (HIVE-1994) Support new annotation @UDFType(stateful = true)
[ https://issues.apache.org/jira/browse/HIVE-1994?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanelfocusedCommentId=12994546#comment-12994546 ] Jonathan Chang commented on HIVE-1994: -- The AND/OR short circuiting is an issue for both SELECT and WHERE. I think stateful UDFs need to poison containing expressions and force them to not short circuit. Support new annotation @UDFType(stateful = true) Key: HIVE-1994 URL: https://issues.apache.org/jira/browse/HIVE-1994 Project: Hive Issue Type: Improvement Components: Query Processor, UDF Reporter: John Sichi Assignee: John Sichi Because Hive does not yet support window functions from SQL/OLAP, people have started hacking around it by writing stateful UDF's for things like cumulative sum. An example is row_sequence in contrib. To clearly mark these, I think we should add a new annotation (with separate semantics from the existing deterministic annotation). I'm proposing the name stateful for lack of a better idea, but I'm open to suggestions. The semantics are as follows: * A stateful UDF can only be used in the SELECT list, not in other clauses such as WHERE/ON/ORDER/GROUP * When a stateful UDF is present in a query, there's an implication that its SELECT needs to be treated as similar to TRANSFORM, i.e. when there's DISTRIBUTE/CLUSTER/SORT clause, then run inside the corresponding reducer to make sure that the results are as expected. For the first one, an example of why we need this is AND/OR short-circuiting; we don't want these optimizations to cause the invocation to be skipped in a confusing way, so we should just ban it outright (which is what SQL/OLAP does for window functions). For the second one, I'm not entirely certain about the details since some of it is lost in the mists in Hive prehistory, but at least if we have the annotation, we'll be able to preserve backwards compatibility as we start adding new cost-based optimizations which might otherwise break it. A specific example would be inserting a materialization step (e.g. for global query optimization) in between the DISTRIBUTE/CLUSTER/SORT and the outer SELECT containing the stateful UDF invocation; this could be a problem if the mappers in the second job subdivides the buckets generated by the first job. So we wouldn't do anything immediately, but the presence of the annotation will help us going forward. -- This message is automatically generated by JIRA. - For more information on JIRA, see: http://www.atlassian.com/software/jira
[jira] Commented: (HIVE-1994) Support new annotation @UDFType(stateful = true)
[ https://issues.apache.org/jira/browse/HIVE-1994?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanelfocusedCommentId=12994581#comment-12994581 ] Adam Kramer commented on HIVE-1994: --- Agree; also consider deprecating DISTRIBUTE/SORT/CLUSTER BY in favor of DISTRIBUTED/SORTED/CLUSTERED BY, a syntax that would explicitly prevent short-circuiting and subdivision for only the query it's a part of. I can't imagine that sort by in the subquery leads to assumptions in the parent query scales well or will last long in any case, but this functionality is not only necessary for backwards-compatibility, but is also kind of the entire reason Hive was developed and/or conceived: To utilize mapreduce functionality in order to transform and process data. Preventing the querier from making mapreduce assumptions just seems sad. Support new annotation @UDFType(stateful = true) Key: HIVE-1994 URL: https://issues.apache.org/jira/browse/HIVE-1994 Project: Hive Issue Type: Improvement Components: Query Processor, UDF Reporter: John Sichi Assignee: John Sichi Because Hive does not yet support window functions from SQL/OLAP, people have started hacking around it by writing stateful UDF's for things like cumulative sum. An example is row_sequence in contrib. To clearly mark these, I think we should add a new annotation (with separate semantics from the existing deterministic annotation). I'm proposing the name stateful for lack of a better idea, but I'm open to suggestions. The semantics are as follows: * A stateful UDF can only be used in the SELECT list, not in other clauses such as WHERE/ON/ORDER/GROUP * When a stateful UDF is present in a query, there's an implication that its SELECT needs to be treated as similar to TRANSFORM, i.e. when there's DISTRIBUTE/CLUSTER/SORT clause, then run inside the corresponding reducer to make sure that the results are as expected. For the first one, an example of why we need this is AND/OR short-circuiting; we don't want these optimizations to cause the invocation to be skipped in a confusing way, so we should just ban it outright (which is what SQL/OLAP does for window functions). For the second one, I'm not entirely certain about the details since some of it is lost in the mists in Hive prehistory, but at least if we have the annotation, we'll be able to preserve backwards compatibility as we start adding new cost-based optimizations which might otherwise break it. A specific example would be inserting a materialization step (e.g. for global query optimization) in between the DISTRIBUTE/CLUSTER/SORT and the outer SELECT containing the stateful UDF invocation; this could be a problem if the mappers in the second job subdivides the buckets generated by the first job. So we wouldn't do anything immediately, but the presence of the annotation will help us going forward. -- This message is automatically generated by JIRA. - For more information on JIRA, see: http://www.atlassian.com/software/jira
