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From "Mamta A. Satoor (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DERBY-6045) in list multi-probe by primary key not chosen on tables with >256 rows
Date Tue, 02 Apr 2013 04:35:16 GMT

    [ https://issues.apache.org/jira/browse/DERBY-6045?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13619507#comment-13619507
] 

Mamta A. Satoor commented on DERBY-6045:
----------------------------------------

Committed changes for this jira with revision 1463378. The commit comments were as follows
****************************************************
DERBY-6045 (in list multi-probe by primary key not chosen on tables with >256 rows)

Changes for DERBY-3790 (Investigate if request for update statistics can be skipped for certain
kind of indexes, one instance may be unique indexes based on one column.) caused Derby to
use table scan rather than index scan since we do not generate stats for single column unique
index. As part of that change, we forgot to make code changes in optimizer to compensate for
missing stats for such indexes. As found in DERBY-6045 (in list multi-probe by primary key
not chosen on tables with >256 rows), even though we do not keep the statistics for single-column
unique indexes, we should improve the selectivity of such an index when the index is being
considered by the optimizer.

Making the relevant code changes now allows us to enable the tests in InListMultiProbeTest.java
since they will now run correctly by picking up index scan rather than table scan.

Additionally, one test in refActions1.sql does not have order by to it and there are only
3 rows in the table. Without the changes for DERBY-6045 we were using index scan for it but
now it uses table scan which is giving the rows in different order. I have added order by
to the query so plan selection does not change order of the rows. The reason behind table
scan might be that with only 3 rows in the table, it is cheaper to do table sccan rather than
index scan. 
****************************************************

                
> in list multi-probe by primary key not chosen on tables with >256 rows
> ----------------------------------------------------------------------
>
>                 Key: DERBY-6045
>                 URL: https://issues.apache.org/jira/browse/DERBY-6045
>             Project: Derby
>          Issue Type: Bug
>          Components: Store
>    Affects Versions: 10.9.1.0, 10.10.1.1
>         Environment: Linux Debian 6.0.5
>            Reporter: Tony Brusseau
>         Attachments: DERBY6045_patch1_diff.txt, DERBY6045_patch2_diff.txt, optimizerTraceOutputFor10_8.txt,
optimizerTraceOutputForTrunk.txt, optimizerTraceOutputWithUpdateStatsFor10_8.txt, optimizerTraceOutputWithUpdateStatsForTrunk.txt
>
>
> I have a table with a long integer primary key field and 11 million rows. I seem to be
unable to load large chunks of rows via id in a reasonably efficient manner.
>   1. If I do individual lookups via the primary key, then a fast indexed lookup occurs.
However, if I do large numbers of such queries, then the time is overwhelmed by round-trip
overhead which makes everything incredibly slow.
>   2. If I use a single query with a disjunction of the primary keys of interest,  then
a table scan is performed (even if the clause only contains 1-3 items), which walks over 11
million rows...incredibly inefficient.
>   3. If I use an IN clause, then a table scan is performed (even if the clause only contains
1-3 items), which walks over 11 million rows...incredibly inefficient.
> I'm guessing that this might have something to do with the fact that I'm using large
integers and really big numbers that don't start anywhere at or about 1 for my keys. Could
this possibly be confusing the optimizer?
> Here are the unlimited query plans for the 3 cases that I enumerated:
> *********************************************************************************************
> [EL Fine]: 2013-01-17 11:09:53.384--ServerSession(582235416)--Connection(1430986883)--Thread(Thread["Initial
Lisp Listener",5,SubL Thread Group])--SELECT TERM_ID, ARG0, ARG1, ARG2, ARG3, FORMULA_HASH,
FORMULA_LENGTH, FORMULA_TYPE, KB_STATUS FROM KB.FORMULA_TERM WHERE (TERM_ID = ?)
> 	bind => [2251799814033500]
> Thu Jan 17 11:09:53 CST 2013 Thread["Initial Lisp Listener",5,SubL Thread Group] (XID
= 4711079), (SESSIONID = 3), SELECT TERM_ID, ARG0, ARG1, ARG2, ARG3, FORMULA_HASH, FORMULA_LENGTH,
FORMULA_TYPE, KB_STATUS FROM KB.FORMULA_TERM WHERE (TERM_ID = ?) ******* Project-Restrict
ResultSet (3):
> Number of opens = 1
> Rows seen = 1
> Rows filtered = 0
> restriction = false
> 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: 1.00
> 	optimizer estimated cost: 6.59
> Source result set:
> 	Index Row to Base Row ResultSet for FORMULA_TERM:
> 	Number of opens = 1
> 	Rows seen = 1
> 	Columns accessed from heap = {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: 1.00
> 		optimizer estimated cost: 6.59
> 		Index Scan ResultSet for FORMULA_TERM using constraint KB_FORMULA_TERM_TERM_ID_PK at
read committed isolation level using share row locking chosen by the optimizer
> 		Number of opens = 1
> 		Rows seen = 1
> 		Rows filtered = 0
> 		Fetch Size = 1
> 			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=3
> 			Number of rows qualified=1
> 			Number of rows visited=1
> 			Scan type=btree
> 			Tree height=-1
> 			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: 1.00
> 			optimizer estimated cost: 6.59
> [EL Fine]: 2013-01-17 11:01:00.732--ServerSession(1237006689)--Connection(927179828)--Thread(Thread["Initial
Lisp Listener",5,SubL Thread Group])--SELECT TERM_ID, ARG0, ARG1, ARG2, ARG3, FORMULA_HASH,
FORMULA_LENGTH, FORMULA_TYPE, KB_STATUS FROM KB.FORMULA_TERM WHERE (((TERM_ID = ?) OR (TERM_ID
= ?)) OR (TERM_ID = ?))
> 	bind => [2251799814033500, 2251799814033501, 2251799814033499]
> Thu Jan 17 11:01:10 CST 2013 Thread["Initial Lisp Listener",5,SubL Thread Group] (XID
= 4711078), (SESSIONID = 3), SELECT TERM_ID, ARG0, ARG1, ARG2, ARG3, FORMULA_HASH, FORMULA_LENGTH,
FORMULA_TYPE, KB_STATUS FROM KB.FORMULA_TERM WHERE (((TERM_ID = ?) OR (TERM_ID = ?)) OR (TERM_ID
= ?)) ******* Project-Restrict ResultSet (3):
> Number of opens = 1
> Rows seen = 3
> Rows filtered = 0
> restriction = false
> 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: 1176730.30
> 	optimizer estimated cost: 5931065.54
> Source result set:
> 	Project-Restrict ResultSet (2):
> 	Number of opens = 1
> 	Rows seen = 11767298
> 	Rows filtered = 11767295
> 	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: 1176730.30
> 		optimizer estimated cost: 5931065.54
> 	Source result set:
> 		Table Scan ResultSet for FORMULA_TERM at read committed isolation level using instantaneous
share row locking chosen by the optimizer
> 		Number of opens = 1
> 		Rows seen = 11767298
> 		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=34358
> 			Number of rows qualified=11767298
> 			Number of rows visited=11767298
> 			Scan type=heap
> 			start position:
> 				null
> 			stop position:
> 				null
> 			qualifiers:
> 				None
> 			optimizer estimated row count: 1176730.30
> 			optimizer estimated cost: 5931065.54
> [EL Fine]: 2013-01-17 11:27:00.627--ServerSession(1237006689)--Connection(1688096771)--Thread(Thread["Initial
Lisp Listener",5,SubL Thread Group])--SELECT TERM_ID, ARG0, ARG1, ARG2, ARG3, FORMULA_HASH,
FORMULA_LENGTH, FORMULA_TYPE, KB_STATUS FROM KB.FORMULA_TERM WHERE (TERM_ID IN (?,?,?))
> 	bind => [2251799814033500, 2251799814033501, 2251799814033499]
> Thu Jan 17 11:47:26 CST 2013 Thread["Initial Lisp Listener",5,SubL Thread Group] (XID
= 4711080), (SESSIONID = 3), SELECT TERM_ID, ARG0, ARG1, ARG2, ARG3, FORMULA_HASH, FORMULA_LENGTH,
FORMULA_TYPE, KB_STATUS FROM KB.FORMULA_TERM WHERE (TERM_ID IN (?,?,?)) ******* Project-Restrict
ResultSet (3):
> Number of opens = 1
> Rows seen = 3
> Rows filtered = 0
> restriction = false
> 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: 1176730.30
> 	optimizer estimated cost: 5931065.54
> Source result set:
> 	Project-Restrict ResultSet (2):
> 	Number of opens = 1
> 	Rows seen = 11767298
> 	Rows filtered = 11767295
> 	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: 1176730.30
> 		optimizer estimated cost: 5931065.54
> 	Source result set:
> 		Table Scan ResultSet for FORMULA_TERM at read committed isolation level using instantaneous
share row locking chosen by the optimizer
> 		Number of opens = 1
> 		Rows seen = 11767298
> 		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=34358
> 			Number of rows qualified=11767298
> 			Number of rows visited=11767298
> 			Scan type=heap
> 			start position:
> 				null
> 			stop position:
> 				null
> 			qualifiers:
> 				None
> 			optimizer estimated row count: 1176730.30
> 			optimizer estimated cost: 5931065.54

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