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https://issues.apache.org/jira/browse/DRILL-4378?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15141403#comment-15141403
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Jinfeng Ni commented on DRILL-4378:
-----------------------------------
Found the place where CONVERT_FROM() is transformed into CONVERT_FROMUTF8().
The logic is in PreProcessLogicalRel[1], where it will convert CONVERT_FROM()
in a Project operator to CONVERT_FROMXXX. The purpose of that transformation
seems to help identify the functions whose output type is complex type. The
DrillMergeProjectRule [2] will check the complex output type as one criteria to
merge two Project operators.
That explains the difference between the direct query case and the view case.
In view case, the CONVERT_FROM() initially is placed in a Project, while the
direct query case will have CONVERT_FROM() in a Filter. Hbase Filter pushdown
logic [3] will look for ConvertExpression ( representing the original
CONVERT_FROM() function). That will make the view case disqualified for filter
pushdown.
There seems to two options: 1) We find some other way to detect complex type
function, without doing such transformation, 2) Modify HBase Filter pushdown
logic, to make it accept CONVERT_FROMXXX() as well.
Option 2 seems to add bunch of redundant code. I still have not a clear idea
about option 1. [~jnadeau], [~mehant], do you have any suggestions?
[1]
https://github.com/apache/drill/blob/master/exec/java-exec/src/main/java/org/apache/drill/exec/planner/logical/PreProcessLogicalRel.java#L101-L102
[2]
https://github.com/apache/drill/blob/master/exec/java-exec/src/main/java/org/apache/drill/exec/planner/logical/DrillMergeProjectRule.java#L59-L62
[3]
https://github.com/apache/drill/blob/master/contrib/storage-hbase/src/main/java/org/apache/drill/exec/store/hbase/CompareFunctionsProcessor.java#L149
> 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
> Assignee: Jinfeng Ni
>
> 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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