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Date: Mon, 17 Jun 2013 19:50:19 +0000 (UTC)
From: "Rick Hillegas (JIRA)" <jira@apache.org>
To: derby-dev@db.apache.org
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Subject: [jira] [Created] (DERBY-6267) Add ability to compactly specify a
 complete query plan in an optimizer override.
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Rick Hillegas created DERBY-6267:
------------------------------------

             Summary: Add ability to compactly specify a complete query plan in an optimizer override.
                 Key: DERBY-6267
                 URL: https://issues.apache.org/jira/browse/DERBY-6267
             Project: Derby
          Issue Type: Improvement
          Components: SQL
    Affects Versions: 10.11.0.0
            Reporter: Rick Hillegas


It would be nice to be able to override the optimizer's choice and specify a complete query plan using the compact summary syntax output by XMLOptTrace. Given how the optimizer handles a statement, this would require binding a query plan at the query block level. Two obvious candidates for such a feature are:

1) Extend the use of DERBY-PROPERTIES in the comments of a query.

2) Add an extra clause to query blocks. The clause would have to be a clearly marked Derby extension.

(1) might look like this (here we add a new "fullQueryPlan" property):

select tablename from sys.systables t, sys.syscolumns c, sys.sysaliases a
where t.tablename = c.columnname and c.columnname = a.alias
-- DERBY-PROPERTIES fullQueryPlan = (SYSCOLUMNS_HEAP # SYSALIASES_INDEX1) # SYSTABLES_INDEX1
union all
select tablename from sys.systables t, sys.syscolumns c, sys.sysaliases a, sys.syssequences s
where t.tablename = c.columnname and c.columnname = a.alias and a.alias = s.sequencename
-- DERBY-PROPERTIES fullQueryPlan = ((SYSCOLUMNS_HEAP # SYSTABLES_INDEX1) # SYSALIASES_INDEX1) # SYSSEQUENCES_INDEX2
;

(2) might look like this (here we add a new "using derby join order" clause):

select tablename from sys.systables t, sys.syscolumns c, sys.sysaliases a
where t.tablename = c.columnname and c.columnname = a.alias
using derby join order (SYSCOLUMNS_HEAP # SYSALIASES_INDEX1) # SYSTABLES_INDEX1
union all
select tablename from sys.systables t, sys.syscolumns c, sys.sysaliases a, sys.syssequences s
where t.tablename = c.columnname and c.columnname = a.alias and a.alias = s.sequencename
using derby join order  ((SYSCOLUMNS_HEAP # SYSTABLES_INDEX1) # SYSALIASES_INDEX1) # SYSSEQUENCES_INDEX2
;

Here's a comparison of these approaches:

(1)
+ Portability: the same query text can be used against different RDBMSes.
- Parsing of DERBY-PROPERTIES happens outside the grammer.

(2)
+ Parsing happens in the parser.
- Not portable.

I slightly prefer approach (1). If I pursue that approach, I would like to see if I can move the parsing into the parser.

I am interested in other opinions about how to address this feature. Thanks.


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