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From "Mike Matrigali (JIRA)" <j...@apache.org>
Subject [jira] Updated: (DERBY-47) Some possible improvements to IN optimization
Date Fri, 23 Feb 2007 00:56:05 GMT

     [ https://issues.apache.org/jira/browse/DERBY-47?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Mike Matrigali updated DERBY-47:
--------------------------------


The multiple probe approach always seemed the most natural to me - as the multiple probe support
was already there
and used by the execution engine (for different reasons) already.  It is great that it looks
like you have found an elegant way
to get the optimizer to cost the approach and throw out cases that approach does not support.
 Part of that was that I understand the mechanics of the multiple probe and didn't understand
the semantics of the query rewrite.

Can you say something
why you chose to use x = ? predicate with special flag vs. just having a new multiple-probe
inlist predicate (this question
may not make sense - I am talking from the outside of your description not from knowledge
of internals).

Also what happens to a query that is effectively an IN list that is hand written using OR's
instead (ie, where i = 1 or i = 2 or ...).
Is that already changed to an IN list before we get to your new code here?

This is probably food for a different discussion, but I was wondering about the costing. 
What is the costing  % number of
rows for a where IN (?)   (ie. a parameter at compile time vs a constant, in a non-unique
index)?  Is this just the cardinality
statistic if it exists?  What  is the default without the statistic?  Where I am going is
that  it probably does not make sense
to have the estimate of the sum of terms be larger than the number of rows in the db.  And
just want to understand how many
terms will it take before we give up on the multiple probe.

> Some possible improvements to IN optimization
> ---------------------------------------------
>
>                 Key: DERBY-47
>                 URL: https://issues.apache.org/jira/browse/DERBY-47
>             Project: Derby
>          Issue Type: Improvement
>          Components: SQL
>    Affects Versions: 10.0.2.0
>         Environment: all
>            Reporter: Sunitha Kambhampati
>         Assigned To: A B
>         Attachments: d47_engine_doNotCommit_v1.patch, d47_engine_doNotCommit_v1.stat,
d47_mp_relOpPredCheck_v1.patch, d47_mp_relOpPredCheck_v1.stat, derby-47-performance-data.txt,
derby-47-performance-data.txt, Derby47PerformanceTest.java, Derby47PerformanceTest.java, InListOperatorNode.java,
QueryPlanUniqueIndexAndWordIndexOneTerm.txt, QueryPlanUniqueIndexAndWordIndexTwoTerms.txt,
QueryPlanUniqueIndexOnlyOneTerm.txt, QueryPlanUniqueIndexOnlyTwoTerms.txt, readlocks.diff,
readlocks_withContext.diff
>
>
> Consider a simple case of  - 
> A table tbl has 10000 rows, there is a primary key index on i1
> and the query in question is 
>  select * from tbl where i1 in (-1,100000)
> derby does a table scan of the entire table even though the "IN" list has only two values
and the comparison is on a field that has an index.
> Briefly looking at the code, it seems like we insert a between and use the IN list to
get the start and stop values for the scan. Thus the range of the values in the "IN" list
here plays an important role. 
> Thus if the query was changed to select * from tbl where i1 in (-1, 1), an index scan
would be chosen.
> It would be nice if we could do something clever in this case where there is clearly
an index on the field and the number of values in the IN list is known. Maybe use the rowcount
estimate and the IN list size to do some optimizations.  
> - consider the length of the "IN" list to do searches on the table.  ie use the IN list
values to do index key searches on the table,
> -or try to convert it to a join. Use the "IN" list values to create a temporary table
and do a join. It is most likely that the optimizer will choose the table with "IN" list here
as the outer table in the join and thus will do key searches on the larger table. 
> -------------------------------------------------------------------
> some query plans that I logged using derby.language.logQueryPlan=true for some similar
queries:
> Table has ascending values from 0 - 9999 for i1. primary key index on i1.
> GMT Thread[UT0,5,main] (XID = 19941), (SESSIONID = 0), select * from scanfixed where
i1 in (-1,9999,9998,9997,9996,9995,9994,9993,9992,9991,9990) ******* Project-Restrict ResultSet
(2):
> Number of opens = 1
> Rows seen = 10000
> Rows filtered = 9990
> restriction = true
> projection = false
> 	constructor time (milliseconds) = 0
> 	open time (milliseconds) = 0
> 	next time (milliseconds) = 0
> 	close time (milliseconds) = 0
> 	restriction time (milliseconds) = 0
> 	projection time (milliseconds) = 0
> 	optimizer estimated row count:          750.38
> 	optimizer estimated cost:         8579.46
> Source result set:
> 	Table Scan ResultSet for SCANFIXED at read committed isolation level using instantaneous
share row locking chosen by the optimizer
> 	Number of opens = 1
> 	Rows seen = 10000
> 	Rows filtered = 0
> 	Fetch Size = 16
> 		constructor time (milliseconds) = 0
> 		open time (milliseconds) = 0
> 		next time (milliseconds) = 0
> 		close time (milliseconds) = 0
> 		next time in milliseconds/row = 0
> 	scan information: 
> 		Bit set of columns fetched=All
> 		Number of columns fetched=9
> 		Number of pages visited=417
> 		Number of rows qualified=10000
> 		Number of rows visited=10000
> 		Scan type=heap
> 		start position: 
> null		stop position: 
> null		qualifiers:
> Column[0][0] Id: 0
> Operator: <=
> Ordered nulls: false
> Unknown return value: false
> Negate comparison result: false
> Column[0][1] Id: 0
> Operator: <
> Ordered nulls: false
> Unknown return value: true
> Negate comparison result: true
> 		optimizer estimated row count:          750.38
> 		optimizer estimated cost:         8579.46
> ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------
> l
> 2004-10-14 18:59:47.577 GMT Thread[UT0,5,main] (XID = 19216), (SESSIONID = 0), select
* from scanfixed where i1 in (9999,9998,9997,9996,9995,9994,9993,9992,9991,9990) ******* Project-Restrict
ResultSet (3):
> Number of opens = 1
> Rows seen = 10
> Rows filtered = 0
> restriction = true
> projection = true
> 	constructor time (milliseconds) = 0
> 	open time (milliseconds) = 0
> 	next time (milliseconds) = 0
> 	close time (milliseconds) = 0
> 	restriction time (milliseconds) = 0
> 	projection time (milliseconds) = 0
> 	optimizer estimated row count:            4.80
> 	optimizer estimated cost:           39.53
> Source result set:
> 	Index Row to Base Row ResultSet for SCANFIXED:
> 	Number of opens = 1
> 	Rows seen = 10
> 	Columns accessed from heap = {0, 1, 2, 3, 4, 5, 6, 7, 8}
> 		constructor time (milliseconds) = 0
> 		open time (milliseconds) = 0
> 		next time (milliseconds) = 0
> 		close time (milliseconds) = 0
> 		optimizer estimated row count:            4.80
> 		optimizer estimated cost:           39.53
> 		Index Scan ResultSet for SCANFIXED using index SCANFIXEDX at read committed isolation
level using instantaneous share row locking chosen by the optimizer
> 		Number of opens = 1
> 		Rows seen = 10
> 		Rows filtered = 0
> 		Fetch Size = 16
> 			constructor time (milliseconds) = 0
> 			open time (milliseconds) = 0
> 			next time (milliseconds) = 0
> 			close time (milliseconds) = 0
> 			next time in milliseconds/row = 0
> 		scan information: 
> 			Bit set of columns fetched=All
> 			Number of columns fetched=2
> 			Number of deleted rows visited=0
> 			Number of pages visited=2
> 			Number of rows qualified=10
> 			Number of rows visited=10
> 			Scan type=btree
> 			Tree height=2
> 			start position: 
> 	>= on first 1 column(s).
> 	Ordered null semantics on the following columns: 
> 			stop position: 
> 	> on first 1 column(s).
> 	Ordered null semantics on the following columns: 
> 			qualifiers:
> None
> 			optimizer estimated row count:            4.80
> 			optimizer estimated cost:           39.53

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