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ASF GitHub Bot commented on DRILL-6115: --------------------------------------- Github user vrozov commented on a diff in the pull request: https://github.com/apache/drill/pull/1110#discussion_r167089878 --- Diff: exec/java-exec/src/main/java/org/apache/drill/exec/physical/base/PhysicalVisitor.java --- @@ -55,10 +56,10 @@ public RETURN visitExchange(Exchange exchange, EXTRA value) throws EXCEP; + public RETURN visitSingleMergeExchange(SingleMergeExchange exchange, EXTRA value) throws EXCEP; --- End diff -- The same question as for `PrelVisitor.java`. Is it necessary to have separate `visitSingleMergeExchange`? > SingleMergeExchange is not scaling up when many minor fragments are allocated > for a query. > ------------------------------------------------------------------------------------------ > > Key: DRILL-6115 > URL: https://issues.apache.org/jira/browse/DRILL-6115 > Project: Apache Drill > Issue Type: Improvement > Components: Execution - Relational Operators > Affects Versions: 1.12.0 > Reporter: Hanumath Rao Maduri > Assignee: Hanumath Rao Maduri > Priority: Major > Fix For: 1.13.0 > > Attachments: Enhancing Drill to multiplex ordered merge exchanges.docx > > > SingleMergeExchange is created when a global order is required in the output. > The following query produces the SingleMergeExchange. > {code:java} > 0: jdbc:drill:zk=local> explain plan for select L_LINENUMBER from > dfs.`/drill/tables/lineitem` order by L_LINENUMBER; > +------+------+ > | text | json | > +------+------+ > | 00-00 Screen > 00-01 Project(L_LINENUMBER=[$0]) > 00-02 SingleMergeExchange(sort0=[0]) > 01-01 SelectionVectorRemover > 01-02 Sort(sort0=[$0], dir0=[ASC]) > 01-03 HashToRandomExchange(dist0=[[$0]]) > 02-01 Scan(table=[[dfs, /drill/tables/lineitem]], > groupscan=[JsonTableGroupScan [ScanSpec=JsonScanSpec > [tableName=maprfs:///drill/tables/lineitem, condition=null], > columns=[`L_LINENUMBER`], maxwidth=15]]) > {code} > On a 10 node cluster if the table is huge then DRILL can spawn many minor > fragments which are all merged on a single node with one merge receiver. > Doing so will create lot of memory pressure on the receiver node and also > execution bottleneck. To address this issue, merge receiver should be > multiphase merge receiver. > Ideally for large cluster one can introduce tree merges so that merging can > be done parallel. But as a first step I think it is better to use the > existing infrastructure for multiplexing operators to generate an OrderedMux > so that all the minor fragments pertaining to one DRILLBIT should be merged > and the merged data can be sent across to the receiver operator. > On a 10 node cluster if each node processes 14 minor fragments. > Current version of code merges 140 minor fragments > the proposed version has two level merges 1 - 14 merge in each drillbit which > is parallel > and 10 minorfragments are merged at the receiver node. -- This message was sent by Atlassian JIRA (v7.6.3#76005)