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From "Knut Anders Hatlen (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DERBY-6267) Add ability to compactly specify a complete query plan in an optimizer override.
Date Fri, 26 Jul 2013 13:01:52 GMT

    [ https://issues.apache.org/jira/browse/DERBY-6267?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13720763#comment-13720763
] 

Knut Anders Hatlen commented on DERBY-6267:
-------------------------------------------

What I tried to say with my last comment was that I wouldn't be worried if we documented the
feature in its current state in the tuning guide. We'll always do our best to preserve compatibility.
And if we have very good reasons to break compatibility, we have mechanisms in place to handle
that via release notes.
                
> 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
>              Labels: derby_triage10_11
>         Attachments: derby-6267-01-ac-compactSyntax.diff, derby-6267-01-ad-compactSyntax.diff,
derby-6267-01-ae-compactSyntax.diff, derby-6267-02-aa-moreTests.diff, derby-6267-03-aa-moreSubqueryTests.diff,
derby-6267-04-aa-fetchOffsetTest.diff
>
>
> 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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