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Posted to derby-dev@db.apache.org by "somebody (JIRA)" <ji...@apache.org> on 2016/01/21 12:03:39 UTC
[jira] [Created] (DERBY-6858) Apache Derby simple update statement
performance becomes 1500% worse when adding one byte to a column
somebody created DERBY-6858:
-------------------------------
Summary: 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: 10.12.1.1, 10.11.1.1
Environment: windows 7 64 bit
Reporter: somebody
Priority: Blocker
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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