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From "somebody (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DERBY-6858) Apache Derby simple update statement performance becomes 1500% worse when adding one byte to a column
Date Thu, 28 Jan 2016 12:20:39 GMT

    [ https://issues.apache.org/jira/browse/DERBY-6858?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15121308#comment-15121308
] 

somebody commented on DERBY-6858:
---------------------------------

The deferrable constraint is needed by my program and regardless, I would think you would
want this issue fixed as most modern databases support deferrable constraints.  I would hope
you would want to optimize deferrable constrains otherwise they have no use since in this
simple small database it causes such a huge performance loss and thus makes them almost completely
useless.

Again I do need this feature for my app so disabling it is not an option.  However, if it
helps you debug the issue and you think there is value in running it against older versions
of derby then you can simply modify the file I gave you and before doing the update on ChildUpdate,
insert another record into ParentUpdate with the same values as was there before, except just
change 'Parent 1' to 'Parent 2' for the new record, then do the update, then delete ParentUpdate
with name 'Parent 1'.  I don't have time to update the app now, but this is a simple change
you can make so you aren't held back in your debugging and fixing.

I don't know if doing the above will have the same performance loss, but that is part of the
debugging.  If you try my above suggestion and you don't see a performance loss, then you
know it's likely the deferred constrains that needs optimizing.  If you do see the performance
decrease then that will also yield information.

I suggest you make the above changes yourself as I don't have time now to make the changes,
but I will help in the future with what I can as usual.

> Apache Derby simple update statement performance becomes 1500% worse when adding one
byte to a column
> -----------------------------------------------------------------------------------------------------
>
>                 Key: DERBY-6858
>                 URL: https://issues.apache.org/jira/browse/DERBY-6858
>             Project: Derby
>          Issue Type: Bug
>    Affects Versions: 10.11.1.1, 10.12.1.1
>         Environment: windows 7 64 bit
>            Reporter: somebody
>            Priority: Blocker
>         Attachments: repro.java, repro.java
>
>
> I have 2 tables as follows:
> ParentUpdate
> name varchar(255)
> value int not null
> primary key: name
> ChildUpdate
> parentName varchar(255)
> name varchar(255)
> value int
> data varchar(1000)
> primary key: name foreign key: parentName to ParentUpdate.name
> When I run the statement "update ChildUpdate set parentName = 'Parent 2' where parentName
= 'Parent 1'" with 2500 records in the ChildUpdate table and 1 record in the ParentUpdate
table with only a single byte difference in data size in the ChildUpdate table, the performance
decreases by 15 times.
> When the ChildUpdate data column has exactly 14 bytes of the same character the runtime
of the above query is about 500 milliseconds. When I add one more byte to the data column
of ChildUpdate the performance all of a sudden becomes about 7500 milliseconds.
> If i then decrease the data size back to 14 from 15 it's fast again. When i put it back
to 15 it's slow again. This is reproducible every time.
> Can you please help me figure out how to get the same fast performance without such seemingly
random behaviour.
> The query plans are below for both cases.
>         projection = true
>             constructor time (milliseconds) = 0
>             open time (milliseconds) = 0
>             next time (milliseconds) = 16
>             close time (milliseconds) = 16
>             restriction time (milliseconds) = 0
>             projection time (milliseconds) = 0
>             optimizer estimated row count: 51.50
>             optimizer estimated cost: 796.12
>         Source result set:
>             Table Scan ResultSet for CHILDUPDATE at read committed isolation level using
exclusive row locking chosen by the optimizer
>             Number of opens = 1
>             Rows seen = 2500
>             Rows filtered = 0
>             Fetch Size = 1
>                 constructor time (milliseconds) = 0
>                 open time (milliseconds) = 15
>                 next time (milliseconds) = 16
>                 close time (milliseconds) = 16
>                 next time in milliseconds/row = 0
>             scan information:
>                 Bit set of columns fetched={0, 1}
>                 Number of columns fetched=2
>                 Number of pages visited=41
>                 Number of rows qualified=2500
>                 Number of rows visited=2500
>                 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
>                 optimizer estimated row count: 51.50
>                 optimizer estimated cost: 796.12
> total time: ~500 milliseconds
> and the slow version
>    Statement Name: 
>     null
> Statement Text: 
>     update ChildUpdate set parentName = 'Parent 2' where parentName = 'Parent 1'
> Parse Time: 0
> Bind Time: 0
> Optimize Time: 0
> Generate Time: 0
> Compile Time: 0
> Execute Time: -1453199485700
> Begin Compilation Timestamp : 2016-01-19 05:31:25.684
> End Compilation Timestamp : 2016-01-19 05:31:25.684
> Begin Execution Timestamp : 2016-01-19 05:31:25.7
> End Execution Timestamp : 2016-01-19 05:31:33.141
> Statement Execution Plan Text: 
> Update ResultSet using row locking:
> deferred: true
> Rows updated = 2500
> Indexes updated = 2
> Execute Time = -1453199485747
>     Normalize ResultSet:
>     Number of opens = 1
>     Rows seen = 2500
>         constructor time (milliseconds) = 0
>         open time (milliseconds) = 0
>         next time (milliseconds) = 47
>         close time (milliseconds) = 0
>         optimizer estimated row count: 51.50
>         optimizer estimated cost: 810.94
>     Source result set:
>         Project-Restrict ResultSet (3):
>         Number of opens = 1
>         Rows seen = 2500
>         Rows filtered = 0
>         restriction = false
>         projection = true
>             constructor time (milliseconds) = 0
>             open time (milliseconds) = 0
>             next time (milliseconds) = 32
>             close time (milliseconds) = 0
>             restriction time (milliseconds) = 0
>             projection time (milliseconds) = 0
>             optimizer estimated row count: 51.50
>             optimizer estimated cost: 810.94
>         Source result set:
>             Project-Restrict ResultSet (2):
>             Number of opens = 1
>             Rows seen = 2500
>             Rows filtered = 0
>             restriction = false
>             projection = true
>                 constructor time (milliseconds) = 0
>                 open time (milliseconds) = 0
>                 next time (milliseconds) = 32
>                 close time (milliseconds) = 0
>                 restriction time (milliseconds) = 0
>                 projection time (milliseconds) = 0
>                 optimizer estimated row count: 51.50
>                 optimizer estimated cost: 810.94
>             Source result set:
>                 Index Scan ResultSet for CHILDUPDATE using index TESTINDEX at read committed
isolation level using exclusive row locking chosen by the optimizer
>                 Number of opens = 1
>                 Rows seen = 2500
>                 Rows filtered = 0
>                 Fetch Size = 1
>                     constructor time (milliseconds) = 0
>                     open time (milliseconds) = 0
>                     next time (milliseconds) = 32
>                     close time (milliseconds) = 0
>                     next time in milliseconds/row = 0
>                 scan information:
>                     Bit set of columns fetched={0, 1, 2}
>                     Number of columns fetched=3
>                     Number of deleted rows visited=0
>                     Number of pages visited=42
>                     Number of rows qualified=2500
>                     Number of rows visited=2500
>                     Scan type=btree
>                     Tree height=2
>                     start position:
>                         None
>                     stop position:
>                         None
>                     qualifiers:
>                         Column[0][0] Id: 1
>                         Operator: =
>                         Ordered nulls: false
>                         Unknown return value: false
>                         Negate comparison result: false
>                     optimizer estimated row count: 51.50
>                     optimizer estimated cost: 810.94
> total time: ~7 seconds 500 milliseconds
> please also see post:
> http://stackoverflow.com/questions/34874762/apache-derby-simple-update-statement-performance-becomes-1500-worse-when-adding



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