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From "John Omernik (JIRA)" <j...@apache.org>
Subject [jira] [Created] (DRILL-4378) CONVERT_FROM in View results in table scan of MapR-DB and perhaps HBASE
Date Tue, 09 Feb 2016 13:54:18 GMT
John Omernik created DRILL-4378:
-----------------------------------

             Summary: CONVERT_FROM in View results in table scan of MapR-DB and perhaps HBASE
                 Key: DRILL-4378
                 URL: https://issues.apache.org/jira/browse/DRILL-4378
             Project: Apache Drill
          Issue Type: Bug
          Components: Query Planning & Optimization, Storage - HBase
    Affects Versions: 1.4.0
            Reporter: John Omernik


 I created a view to avoid forcing users to write queries that always included the CONVERT_FROM
statements. (I am a huge advocate of making things easy for the the users and writing queries
with CONVERT_FROM statements isn't easy). 

I ran a query the other day on one of these views and noticed that a query that took 30 seconds
really shouldn't take 30 seconds.  What do I mean? well I wanted to get part of a record by
looking up the MapR-DB Row key (equiv. to HBASE row key)  That should be an instant lookup.
 Sure enough, when I tried it in the hbase shell that returns instantly.  So why did Drill
take 30 seconds?  I shot an email to Ted and Jim at MapR to ask this very question. Ted suggested
that I try the query without a view.  Sure enough, If I use the convert_from in a direct query,
it's an instant (sub second) return.  Thus it appears something in the view is not allowing
the query to short circuit the read.  

Ted suggests I post here  (I am curious if anyone who has HBASE setup is seeing this same
issue with views) but also include the EXPLAIN plan.  Basically, using my very limited ability
to read EXPLAIN plans (If someone has a pointer to a blog post or docs on how to read EXPLAIN
I would love that!) it looks like in the view the startRow and stopRow in the hbaseScanSpec
are not set, seeming to cause a scan.  Is there any away to assist the planner when running
this through a view so that we can get the performance of the query without the view but with
the easy of use/readability of using the view?

Thanks!!!

John

View Creation

CREATE VIEW view_testpaste as 
SELECT 
CONVERT_FROM(row_key, 'UTF8') AS pasteid,
CONVERT_FROM(pastes.pdata.lang, 'UTF8') AS lang,
CONVERT_FROM(pastes.raw.paste, 'UTF8') AS paste
FROM dfs.`pastes`.`/pastes` pastes;


Select from view takes 32 seconds (seems to be a scan)

> select paste from view_testpaste where pasteid = 'djHEHcPM'

1 row selected (32.302 seconds)


Just a direct select returns very fast (0.486 seconds)

> select CONVERT_FROM(pastes.raw.paste, 'UTF8') AS paste
FROM dfs.`pastes`.`/pastes` pastes where 
CONVERT_FROM(row_key, 'UTF8') = 'djHEHcPM';

1 row selected (0.486 seconds)




EXPLAIN PLAN FOR select paste from view_testpaste where pasteid = 'djHEHcPM'

+------+------+
| text | json |
+------+------+
| 00-00    Screen
00-01      UnionExchange
01-01        Project(paste=[CONVERT_FROMUTF8($1)])
01-02          SelectionVectorRemover
01-03            Filter(condition=[=(CONVERT_FROMUTF8($0), 'djHEHcPM')])
01-04              Project(row_key=[$1], ITEM=[ITEM($0, 'paste')])
01-05                Scan(groupscan=[MapRDBGroupScan [HBaseScanSpec=HBaseScanSpec [tableName=maprfs:///data/pastebiner/pastes,
startRow=null, stopRow=null, filter=null], columns=[`row_key`, `raw`.`paste`]]])
 | {
  "head" : {
    "version" : 1,
    "generator" : {
      "type" : "ExplainHandler",
      "info" : ""
    },
    "type" : "APACHE_DRILL_PHYSICAL",
    "options" : [ ],
    "queue" : 0,
    "resultMode" : "EXEC"
  },
  "graph" : [ {
    "pop" : "maprdb-scan",
    "@id" : 65541,
    "userName" : "darkness",
    "hbaseScanSpec" : {
      "tableName" : "maprfs:///data/pastebiner/pastes",
      "startRow" : "",
      "stopRow" : "",
      "serializedFilter" : null
    },
    "storage" : {
      "type" : "file",
      "enabled" : true,
      "connection" : "maprfs:///",
      "workspaces" : {
        "root" : {
          "location" : "/",
          "writable" : false,
          "defaultInputFormat" : null
        },
         "pastes" : {
          "location" : "/data/pastebiner",
          "writable" : true,
          "defaultInputFormat" : null
        },
        "dev" : {
          "location" : "/data/dev",
          "writable" : true,
          "defaultInputFormat" : null
        },
        "hive" : {
          "location" : "/user/hive",
          "writable" : true,
          "defaultInputFormat" : null
        },
        "tmp" : {
          "location" : "/tmp",
          "writable" : true,
          "defaultInputFormat" : null
        }
      },
      "formats" : {
        "psv" : {
          "type" : "text",
          "extensions" : [ "tbl" ],
          "delimiter" : "|"
        },
        "csv" : {
          "type" : "text",
          "extensions" : [ "csv" ],
          "escape" : "`",
          "delimiter" : ","
        },
        "tsv" : {
          "type" : "text",
          "extensions" : [ "tsv" ],
          "delimiter" : "\t"
        },
        "parquet" : {
          "type" : "parquet"
        },
        "json" : {
          "type" : "json"
        },
        "maprdb" : {
          "type" : "maprdb"
        }
      }
    },
    "columns" : [ "`row_key`", "`raw`.`paste`" ],
    "cost" : 573950.0
  }, {
    "pop" : "project",
    "@id" : 65540,
    "exprs" : [ {
      "ref" : "`row_key`",
      "expr" : "`row_key`"
    }, {
      "ref" : "`ITEM`",
      "expr" : "`raw`.`paste`"
    } ],
    "child" : 65541,
    "initialAllocation" : 1000000,
    "maxAllocation" : 10000000000,
    "cost" : 573950.0
  }, {
    "pop" : "filter",
    "@id" : 65539,
    "child" : 65540,
    "expr" : "equal(convert_fromutf8(`row_key`) , 'djHEHcPM') ",
    "initialAllocation" : 1000000,
    "maxAllocation" : 10000000000,
    "cost" : 86092.5
  }, {
    "pop" : "selection-vector-remover",
    "@id" : 65538,
    "child" : 65539,
    "initialAllocation" : 1000000,
    "maxAllocation" : 10000000000,
    "cost" : 86092.5
  }, {
    "pop" : "project",
    "@id" : 65537,
    "exprs" : [ {
      "ref" : "`paste`",
      "expr" : "convert_fromutf8(`ITEM`) "
    } ],
    "child" : 65538,
    "initialAllocation" : 1000000,
    "maxAllocation" : 10000000000,
    "cost" : 86092.5
  }, {
    "pop" : "union-exchange",
    "@id" : 1,
    "child" : 65537,
    "initialAllocation" : 1000000,
    "maxAllocation" : 10000000000,
    "cost" : 86092.5
  }, {
    "pop" : "screen",
    "@id" : 0,
    "child" : 1,
    "initialAllocation" : 1000000,
    "maxAllocation" : 10000000000,
    "cost" : 86092.5
  } ]
} |
+------+------+
1 row selected (0.42 seconds)



EXPLAIN PLAN FOR select CONVERT_FROM(pastes.raw.paste, 'UTF8') AS paste
FROM dfs.`pastes`.`/pastes` pastes where 
CONVERT_FROM(row_key, 'UTF8') = 'djHEHcPM';

+------+------+
| text | json |
+------+------+
| 00-00    Screen
00-01      Project(paste=[CONVERT_FROMUTF8($1)])
00-02        Project(row_key=[$1], ITEM=[ITEM($0, 'paste')])
00-03          Scan(groupscan=[MapRDBGroupScan [HBaseScanSpec=HBaseScanSpec [tableName=maprfs:///data/pastebiner/pastes,
startRow=djHEHcPM, stopRow=djHEHcPM\x00, filter=RowFilter (EQUAL, djHEHcPM)], columns=[`row_key`,
`raw`.`paste`]]])
 | {
  "head" : {
    "version" : 1,
    "generator" : {
      "type" : "ExplainHandler",
      "info" : ""
    },
    "type" : "APACHE_DRILL_PHYSICAL",
    "options" : [ ],
    "queue" : 0,
    "resultMode" : "EXEC"
  },
  "graph" : [ {
    "pop" : "maprdb-scan",
    "@id" : 3,
    "userName" : "darkness",
    "hbaseScanSpec" : {
      "tableName" : "maprfs:///data/pastebiner/pastes",
      "startRow" : "ZGpIRUhjUE0=",
      "stopRow" : "ZGpIRUhjUE0A",
      "serializedFilter" : "CihvcmcuYXBhY2hlLmhhZG9vcC5oYmFzZS5maWx0ZXIuUm93RmlsdGVyEkUKQwgCEj8KL29yZy5hcGFjaGUuaGFkb29wLmhiYXNlLmZpbHRlci5CaW5hcnlDb21wYXJhdG9yEgwKCgoIZGpIRUhjUE0="
    },
    "storage" : {
      "type" : "file",
      "enabled" : true,
      "connection" : "maprfs:///",
      "workspaces" : {
        "root" : {
          "location" : "/",
          "writable" : false,
          "defaultInputFormat" : null
        },
        "pastes" : {
          "location" : "/data/pastebiner",
          "writable" : true,
          "defaultInputFormat" : null
        },
        "dev" : {
          "location" : "/data/dev",
          "writable" : true,
          "defaultInputFormat" : null
        },
        "hive" : {
          "location" : "/user/hive",
          "writable" : true,
          "defaultInputFormat" : null
        },
        "tmp" : {
          "location" : "/tmp",
          "writable" : true,
          "defaultInputFormat" : null
        }
      },
      "formats" : {
        "psv" : {
          "type" : "text",
          "extensions" : [ "tbl" ],
          "delimiter" : "|"
        },
        "csv" : {
          "type" : "text",
          "extensions" : [ "csv" ],
          "escape" : "`",
          "delimiter" : ","
        },
        "tsv" : {
          "type" : "text",
          "extensions" : [ "tsv" ],
          "delimiter" : "\t"
        },
        "parquet" : {
          "type" : "parquet"
        },
        "json" : {
          "type" : "json"
        },
        "maprdb" : {
          "type" : "maprdb"
        }
      }
    },
    "columns" : [ "`row_key`", "`raw`.`paste`" ],
    "cost" : 286975.0
  }, {
    "pop" : "project",
    "@id" : 2,
    "exprs" : [ {
      "ref" : "`row_key`",
      "expr" : "`row_key`"
    }, {
      "ref" : "`ITEM`",
      "expr" : "`raw`.`paste`"
    } ],
    "child" : 3,
    "initialAllocation" : 1000000,
    "maxAllocation" : 10000000000,
    "cost" : 286975.0
  }, {
    "pop" : "project",
    "@id" : 1,
    "exprs" : [ {
      "ref" : "`paste`",
      "expr" : "convert_fromutf8(`ITEM`) "
    } ],
    "child" : 2,
    "initialAllocation" : 1000000,
    "maxAllocation" : 10000000000,
    "cost" : 286975.0
  }, {
    "pop" : "screen",
    "@id" : 0,
    "child" : 1,
    "initialAllocation" : 1000000,
    "maxAllocation" : 10000000000,
    "cost" : 286975.0
  } ]
} |



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