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https://issues.apache.org/jira/browse/PHOENIX-4845?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16868090#comment-16868090
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Daniel Wong commented on PHOENIX-4845:
--------------------------------------
So I have began implementing this Jira and have done some initial scoping and
approach thoughts.
Disallowed cases will not be supported:
{code:java}
//Test RVC Offset columns must be coercible to a base table
@Test
public void testRVCIndexLookup() throws SQLException {
String failureSql = String.format("SELECT t_id, k1, k2 FROM %s OFFSET ('a',
'ab', 2)",tableName);
try {
conn.createStatement().execute(failureSql);
} catch (Exception e) {
System.out.println(e.getMessage());
return;
}
fail("Should not allow Index lookup with RVC Offset");
}
//Test Not Allow Index Access Path On Base Table
@Test
public void testRVCOffsetNotCoercible() throws SQLException {
String failureSql = String.format("SELECT t_id, k1, k2 FROM %s OFFSET ('a',
'ab', 2)",tableName);
try {
conn.createStatement().execute(failureSql);
} catch (Exception e) {
System.out.println(e.getMessage());
return;
}
fail("Should not allow non coercible values to PK in RVC Offset");
}
//Test Order By Not PK Order By Exception
@Test
public void testRVCOffsetNotAllowNonPKOrderBy() throws SQLException {
String failureSql = String.format("SELECT t_id, k1, k2, v1 FROM %s ORDER BY v1
OFFSET ('a', 1, 2)",tableName);
try {
conn.createStatement().execute(failureSql);
} catch (Exception e) {
System.out.println(e.getMessage());
return;
}
fail("Should not allow no PK order by with RVC Offset");
}
//Test Order By Partial PK Order By Exception
@Test
public void testRVCOffsetNotAllowPartialPKOrderBy() throws SQLException {
String failureSql = String.format("SELECT t_id, k1, k2 FROM %s ORDER BY 2
OFFSET ('a', 1, 2)",tableName);
try {
conn.createStatement().execute(failureSql);
} catch (Exception e) {
System.out.println(e.getMessage());
return;
}
fail("Should not allow partial PK order by with RVC Offset");
}
//Test Order By Not PK Order By Exception
@Test
public void testRVCOffsetNotAllowDifferentPKOrderBy() throws SQLException {
String failureSql = String.format("SELECT t_id, k1, k2 FROM %s ORDER BY 1
DESC,2,3 OFFSET ('a', 1, 2)",tableName);
try {
conn.createStatement().execute(failureSql);
} catch (Exception e) {
System.out.println(e.getMessage());
return;
}
fail("Should not allow differnt PK order by with RVC Offset");
}
//Test Not allow joins
@Test
public void testRVCOffsetNotAllowedInJoins() throws SQLException {
String failureSql = String.format("SELECT * FROM %s AS T1, %s AS T2 WHERE
T1.t_id=T2.t_id OFFSET ('a', 1, 2)",tableName,tableName); //literal works
try {
conn.createStatement().execute(failureSql);
} catch (Exception e) {
System.out.println(e.getMessage());
return;
}
fail("Should not have JOIN in RVC Offset");
}
//Test Not allowed in subsquery
@Test
public void testRVCOffsetNotAllowedInSubQuery() throws SQLException {
String failureSql = String.format("SELECT * FROM (SELECT t_id, k2 FROM %s
OFFSET ('a', 1, 2))",tableName);
try {
conn.createStatement().execute(failureSql);
} catch (Exception e) {
System.out.println(e.getMessage());
return;
}
fail("Should not have subquery with RVC Offset");
}
//Test Not allowed on subsquery
@Test
public void testRVCOffsetNotAllowedOnSubQuery() throws SQLException {
String failureSql = String.format("SELECT * FROM (SELECT t_id, k2 FROM %s)
OFFSET ('a', 1, 2)",tableName);
try {
conn.createStatement().execute(failureSql);
} catch (Exception e) {
System.out.println(e.getMessage());
return;
}
fail("Should not have subquery with RVC Offset");
}
//Test RVC Offset must be a literal, cannot have column reference
@Test
public void testRVCOffsetLiteral() throws SQLException {
String sql = "SELECT * FROM " + tableName + " OFFSET ('a', 1, 2)"; //literal
works
conn.createStatement().execute(sql);
String failureSql = "SELECT * FROM " + tableName + " OFFSET ('a', 1, k2)";
//column does works
try {
conn.createStatement().execute(failureSql);
} catch (Exception e) {
System.out.println(e.getMessage());
return;
}
fail("Should not have allowed column in RVC Offset");
}
{code}
Approach Possibilities:
I have been considering 2 posibilities for approaching this in Phoenix and am
open to other suggestions as well.
Given DDL/Query:
Create Table TABLE (a UNSIGNED_TINYINT, b UNSIGNED_TINYINT, c UNSIGNED_TINYINT,
CONSTANT pk PRIMARY KEY (a,b desc, c))
SELECT * FROM TABLE OFFSET (1,2,3)
Approach 1: Query Rewrite
SELECT * FROM TABLE OFFSET (1,2,3)
->
SELECT * FROM TABLE WHERE (A > 1 OR (A = 1 AND (B < 2 OR (B = 2 AND (C >=
3)))))
Approach 2: Mini - Resolution
SELECT * FROM TABLE OFFSET (1,2,3)
-> SELECT 1 FROM TABLE WHERE (a,b,c)=(1,2,3), (Pass the constructed tree to
the WhereOptimizer essentially)
-> Extract Byte Array From Constant [0x01FD03]
-> Filter Scans start/end key by Constant
Right now I'm favoring approach 2 but this will require some additional hooks
into the scan generation. Any one else have thoughts? [~tdsilva]
[~jamestaylor] [~lhofhansl]
> Support using Row Value Constructors in OFFSET clause for paging in tables
> where the sort order of PK columns varies
> --------------------------------------------------------------------------------------------------------------------
>
> Key: PHOENIX-4845
> URL: https://issues.apache.org/jira/browse/PHOENIX-4845
> Project: Phoenix
> Issue Type: New Feature
> Reporter: Thomas D'Silva
> Assignee: Daniel Wong
> Priority: Major
> Labels: DESC, SFDC
> Attachments: PHOENIX-offset.txt
>
>
> RVCs along with the LIMIT clause are useful for efficiently paging through
> rows (see [http://phoenix.apache.org/paged.html]). This works well if the pk
> columns are sorted ascending, we can always use the > operator to query for
> the next batch of row.
> However if the PK of a table is (A DESC, B DESC) we cannot use the following
> query to page through the data
> {code:java}
> SELECT * FROM TABLE WHERE (A, B) > (?, ?) ORDER BY A DESC, B DESC LIMIT 20
> {code}
> Since the rows are sorted by A desc and then by B descending we need change
> the comparison order
> {code:java}
> SELECT * FROM TABLE WHERE (A, B) < (?, ?) ORDER BY A DESC, B DESC LIMIT 20
> {code}
> If the PK of a table contains columns with mixed sort order for eg (A DESC,
> B) then we cannot use RVC to page through data.
> If we supported using RVCs in the offset clause we could use the offset to
> set the start row of the scan. Clients would not have to have logic to
> determine the comparison operator. This would also support paging through
> data for tables where the PK columns are sorted in mixed order.
> {code:java}
> SELECT * FROM TABLE ORDER BY A DESC, B LIMIT 20 OFFSET (?,?)
> {code}
> We would only allow using the offset if the rows are ordered by the sort
> order of the PK columns.
>
> FYI [~jfernando_sfdc]
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