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From "Bryan Pendleton (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-47) Some possible improvements to IN optimization
Date Tue, 13 Mar 2007 20:12:10 GMT

    [ https://issues.apache.org/jira/browse/DERBY-47?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12480534
] 

Bryan Pendleton commented on DERBY-47:
--------------------------------------

Hi Army, I had a look at the preprocess and master patches and they look
good to me. Here's a couple small thoughts I had which you might want to
consider down the road.

0) You are right about the compound IF statement that we discussed in the
   previous set of comments. I misread the logic, and I agree that there is
   not any NPE hole there. Thanks for the further explanation.

1) In one of the comments, you said:

   We intentionally use a parameter node instead of a constant node 
   because the IN-list has more than one value 

   It's not *always* true that the IN-list has more than one value, right?
   That is, it would be legal, if not very useful, to write

   SELECT * FROM t WHERE c IN (1)

   As I read the code near that comment, it didn't seem that you were actually
   depending on the IN-list having more than one value. Rather, you were
   choosing a data structure which could handle multiple values, but which can
   handle a single value just as well.

   But I thought I'd mention it just to be sure.

2) Do you have any test cases of the form

   WHERE c IN (SELECT c_prime from t_prime)

   That is, where the IN-list is neither a list of literal constants, nor a
   list of parameter markers, but is instead a subquery whose values will
   be used as the list.

   Does such a query generate and use the new style Multi-Probe processing?

3) Do you have any test cases in which the IN-list predicate references a
   column in a UNION or a UNION view, thus requiring pushing the IN-list
   predicate down and pulling it back up?

4) In the change to OrNode.java, my eye was caught by the variable name "beon".
   I've seen that a common convention is to use an acronym, so maybe "beon"
   stood for Binary Equality Operator Node, or something like that, but the
   actual datatype is Binary*Relational*OperatorNode, so I would have
   expected to see a variable "bron".

   BinaryRelationalOperatorNode beon = null;

   It's totally unimportant, but I saw it and thought I'd mention it.

5) I looked at the updated masters; to my eye they show that the new probe
   predicate is working, and the optimizer is choosing to use index-to-base
   processing for these predicates rather than the formerly-chosen table
   scans, so this looks great to me.

6) I have no guidance to offer regarding the readlocks diff, sorry.

7) For some reason, I expected to see something more vivid indicating the
   use of the new execution strategy in the query plans, I thought maybe I'd
   see something like "MultiProbeTableScanResultSet" in query dumps? Is it
   just these tests that don't show that, and other query dumps would? Or is
   the only indication that the new probing code has been chosen the use of
   the index in place of the table scan?


> 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_addlTestCases.patch, d47_mp_CBO_MoAP_v1.patch, d47_mp_CBO_MoAP_v1.stat, d47_mp_codeGen_v1.patch,
d47_mp_codeGen_v1.stat, d47_mp_exec_v1.patch, d47_mp_exec_v1.stat, d47_mp_masters_v1.patch,
d47_mp_preprocess_v1.patch, d47_mp_preprocess_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, 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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