{"action":"created","comment":{"url":"https://api.github.com/repos/apache/spark/pulls/comments/49544284","id":49544284,"diff_hunk":"@@ -200,41 +200,60 @@ object HiveTypeCoercion {\n    */\n   object WidenSetOperationTypes extends Rule[LogicalPlan] {\n \n-    private[this] def widenOutputTypes(\n-        planName: String,\n-        left: LogicalPlan,\n-        right: LogicalPlan): (LogicalPlan, LogicalPlan) = {\n-      require(left.output.length == right.output.length)\n-\n-      val castedTypes = left.output.zip(right.output).map {\n-        case (lhs, rhs) if lhs.dataType != rhs.dataType =>\n-          findWiderTypeForTwo(lhs.dataType, rhs.dataType)\n-        case other => None\n+    private def widenOutputTypes(children: Seq[LogicalPlan]): Seq[LogicalPlan] = {\n+      require(children.forall(_.output.length == children.head.output.length))\n+\n+      // Get a sequence of data types, each of which is the widest type of this specific attribute\n+      // in all the children\n+      val castedTypes: Seq[Option[DataType]] = {","path":"sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/HiveTypeCoercion.scala","position":28,"original_position":28,"commit_id":"f3d23dc452afa5d6848cf4469751f33cf3036f57","original_commit_id":"f3d23dc452afa5d6848cf4469751f33cf3036f57","user":{"login":"cloud-fan","id":3182036,"avatar_url":"https://avatars.githubusercontent.com/u/3182036?v=3","gravatar_id":"","url":"https://api.github.com/users/cloud-fan","html_url":"https://github.com/cloud-fan","followers_url":"https://api.github.com/users/cloud-fan/followers","following_url":"https://api.github.com/users/cloud-fan/following{/other_user}","gists_url":"https://api.github.com/users/cloud-fan/gists{/gist_id}","starred_url":"https://api.github.com/users/cloud-fan/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/cloud-fan/subscriptions","organizations_url":"https://api.github.com/users/cloud-fan/orgs","repos_url":"https://api.github.com/users/cloud-fan/repos","events_url":"https://api.github.com/users/cloud-fan/events{/privacy}","received_events_url":"https://api.github.com/users/cloud-fan/received_events","type":"User","site_admin":false},"body":"instead of doing it in batch, can we just iterate children multiple times and handle one column each time? We can stop iterating once we find a column is not type-coerce-able among children. Also we should not touch the original plan if there exists any non-type-coerce-able column.","created_at":"2016-01-13T02:14:13Z","updated_at":"2016-01-13T02:14:13Z","html_url":"https://github.com/apache/spark/pull/10577#discussion_r49544284","pull_request_url":"https://api.github.com/repos/apache/spark/pulls/10577","_links":{"self":{"href":"https://api.github.com/repos/apache/spark/pulls/comments/49544284"},"html":{"href":"https://github.com/apache/spark/pull/10577#discussion_r49544284"},"pull_request":{"href":"https://api.github.com/repos/apache/spark/pulls/10577"}}},"pull_request":{"url":"https://api.github.com/repos/apache/spark/pulls/10577","id":55018138,"html_url":"https://github.com/apache/spark/pull/10577","diff_url":"https://github.com/apache/spark/pull/10577.diff","patch_url":"https://github.com/apache/spark/pull/10577.patch","issue_url":"https://api.github.com/repos/apache/spark/issues/10577","number":10577,"state":"open","locked":false,"title":"[SPARK-12616] [SQL] Making Logical Operator `Union` Support Arbitrary Number of Children","user":{"login":"gatorsmile","id":11567269,"avatar_url":"https://avatars.githubusercontent.com/u/11567269?v=3","gravatar_id":"","url":"https://api.github.com/users/gatorsmile","html_url":"https://github.com/gatorsmile","followers_url":"https://api.github.com/users/gatorsmile/followers","following_url":"https://api.github.com/users/gatorsmile/following{/other_user}","gists_url":"https://api.github.com/users/gatorsmile/gists{/gist_id}","starred_url":"https://api.github.com/users/gatorsmile/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/gatorsmile/subscriptions","organizations_url":"https://api.github.com/users/gatorsmile/orgs","repos_url":"https://api.github.com/users/gatorsmile/repos","events_url":"https://api.github.com/users/gatorsmile/events{/privacy}","received_events_url":"https://api.github.com/users/gatorsmile/received_events","type":"User","site_admin":false},"body":"The existing `Union` logical operator only supports two children. Thus, adding a new logical operator `Unions` which can have arbitrary number of children to replace the existing one.\r\n\r\n`Union` logical plan is a binary node. However, a typical use case for union is to union a very large number of input sources (DataFrames, RDDs, or files). It is not uncommon to union hundreds of thousands of files. In this case, our optimizer can become very slow due to the large number of logical unions. We should change the Union logical plan to support an arbitrary number of children, and add a single rule in the optimizer to collapse all adjacent `Unions` into a single `Unions`. Note that this problem doesn't exist in physical plan, because the physical `Unions` already supports arbitrary number of children.","created_at":"2016-01-04T20:27:50Z","updated_at":"2016-01-13T02:14:13Z","closed_at":null,"merged_at":null,"merge_commit_sha":"93bee78b345797c2a074560b6befc2888c4f0b26","assignee":null,"milestone":null,"commits_url":"https://api.github.com/repos/apache/spark/pulls/10577/commits","review_comments_url":"https://api.github.com/repos/apache/spark/pulls/10577/comments","review_comment_url":"https://api.github.com/repos/apache/spark/pulls/comments{/number}","comments_url":"https://api.github.com/repos/apache/spark/issues/10577/comments","statuses_url":"https://api.github.com/repos/apache/spark/statuses/f3d23dc452afa5d6848cf4469751f33cf3036f57","head":{"label":"gatorsmile:unionAllMultiChildren","ref":"unionAllMultiChildren","sha":"f3d23dc452afa5d6848cf4469751f33cf3036f57","user":{"login":"gatorsmile","id":11567269,"avatar_url":"https://avatars.githubusercontent.com/u/11567269?v=3","gravatar_id":"","url":"https://api.github.com/users/gatorsmile","html_url":"https://github.com/gatorsmile","followers_url":"https://api.github.com/users/gatorsmile/followers","following_url":"https://api.github.com/users/gatorsmile/following{/other_user}","gists_url":"https://api.github.com/users/gatorsmile/gists{/gist_id}","starred_url":"https://api.github.com/users/gatorsmile/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/gatorsmile/subscriptions","organizations_url":"https://api.github.com/users/gatorsmile/orgs","repos_url":"https://api.github.com/users/gatorsmile/repos","events_url":"https://api.github.com/users/gatorsmile/events{/privacy}","received_events_url":"https://api.github.com/users/gatorsmile/received_events","type":"User","site_admin":false},"repo":{"id":44710950,"name":"spark","full_name":"gatorsmile/spark","owner":{"login":"gatorsmile","id":11567269,"avatar_url":"https://avatars.githubusercontent.com/u/11567269?v=3","gravatar_id":"","url":"https://api.github.com/users/gatorsmile","html_url":"https://github.com/gatorsmile","followers_url":"https://api.github.com/users/gatorsmile/followers","following_url":"https://api.github.com/users/gatorsmile/following{/other_user}","gists_url":"https://api.github.com/users/gatorsmile/gists{/gist_id}","starred_url":"https://api.github.com/users/gatorsmile/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/gatorsmile/subscriptions","organizations_url":"https://api.github.com/users/gatorsmile/orgs","repos_url":"https://api.github.com/users/gatorsmile/repos","events_url":"https://api.github.com/users/gatorsmile/events{/privacy}","received_events_url":"https://api.github.com/users/gatorsmile/received_events","type":"User","site_admin":false},"private":false,"html_url":"https://github.com/gatorsmile/spark","description":"Mirror 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