Re: A Tale of Two SQLs
- From: "Jonathan Lewis" <jonathan@xxxxxxxxxxxxxxxxxx>
- To: <oracle-l@xxxxxxxxxxxxx>
- Date: Mon, 3 May 2004 21:45:15 +0100
Something has to be updating one of the tables
or you couldn't get ORA-01555. I would check
to see if any of the code is doing 'select for update'
rather than a simple 'update'. There are versions
of Oracle where 'select for update' can result in
large numbers of CR copies of blocks and produces
the symptoms you've described.
Another possibility is that there is something about
the data and index on T3 with it "less than" clause
which results in identical access paths, but extremely
different amounts of work being done as the data
changes over discrete time intervals. The execution
path, index definitions, and column types might give
a clue.
Regards
Jonathan Lewis
http://www.jlcomp.demon.co.uk
The Co-operative Oracle Users' FAQ
http://www.jlcomp.demon.co.uk/faq/ind_faq.html
Optimising Oracle Seminar
http://www.jlcomp.demon.co.uk/seminar.html
June 2004 UK Manchester
July 2004 Iceland
July 2004 USA California
Aug 2004 USA North Carolina
Sept 2004 UK Manchester
Sept 2004 USA NYC
Oct 2004 USA Boston
----- Original Message -----
From: "Daniel Fink" <Daniel.Fink@xxxxxxx>
To: <oracle-l@xxxxxxxxxxxxx>
Sent: Monday, May 03, 2004 9:05 PM
Subject: A Tale of Two SQLs
It was the best of sql executions; it was the worst of sql
executions.
We have a process that periodically slows down. So far, we have
not been able to pinpoint a root cause, but we continue to
pester the development/application support folks for more info.
I apologize for the limited information, but I'm hoping that we
are aiming in the right direction.
We are smart enough that we captured a 10046 trace during a good
execution as a baseline. I have tagged the lines from this trace
file as (good). This morning, the query began slowing down
(eventually it will get a 1555 error). We turned on tracing and
those lines are tagged as (bad).
To make sure I am comparing apples to apples, the statements are
identical, even the bind variables are identical. I'm not going
to post the 2 trace files (almost 500m), so I'm including the
relevant parts. There are no waits in these execution/fetches
(you read it correctly, no db file waits, no sql*net waits).
I've also changed the statments to remove any table/column
names.
What I have found is that the first FETCH of the bad execution
is significantly (300 - 700x) slower than the good execution. It
also performs significantly more (500x) consistent reads.
Subsequent FETCHes are nearly identical to each other (in terms
of good = bad). These FETCHes are performed tens of thousands of
times as this query is re-executed with different bind variables
(also note the time difference in the EXECs, but it pales in
comparison).
My theory is that the high number of crs in the first FETCH of
each execution are the result of building a read-consistent
version of the data. Again, we are working with the dev/app
folks to confirm that one of these tables is being modified, but
have not had a response yet.
Comments on my theory?
'Tis a far, far better thing I do...
Daniel
Bad SQL
=====================
PARSING IN CURSOR #10(bad) len=295 dep=1 uid=86 oct=3 lid=86
tim=746385804887 hv=3414111617 ad='93b1bcf0'
SELECT t1.col1
from table1 t1, table2 t2
where t2.col2 = :b1 and t2.col2 = t1.col2
union
select max(t3.col3)
from table3 t3
where t3.col4 = substr(:b1, 1, 6) and t3.col3 < :b1
END OF STMT
Good SQL
=====================
PARSING IN CURSOR #7(good) len=295 dep=1 uid=63 oct=3 lid=63
tim=26349629222266 hv=3414111617 ad='8c9aee70'
SELECT t1.col1
from table1 t1, table2 t2
where t2.col2 = :b1 and t2.col2 = t1.col2
union
select max(t3.col3)
from table3 t3
where t3.col4 = substr(:b1, 1, 6) and t3.col3 < :b1
END OF STMT
EXEC
#10(bad):c=0,e=701,p=0,cr=0,cu=0,mis=0,r=0,dep=1,og=4,tim=746385804872
EXEC
#7(good):c=0,e=536,p=0,cr=0,cu=0,mis=0,r=0,dep=1,og=4,tim=26349629222259
FETCH
#10(bad):c=110000,e=107303,p=0,cr=7699,cu=0,mis=0,r=1,dep=1,og=4,tim=7463859
12781
FETCH
#7(good):c=0,e=406,p=0,cr=16,cu=0,mis=0,r=1,dep=1,og=4,tim=26349629222976
FETCH
#10(bad):c=0,e=30,p=0,cr=0,cu=0,mis=0,r=0,dep=1,og=4,tim=746385913106
FETCH
#7(good):c=0,e=31,p=0,cr=0,cu=0,mis=0,r=0,dep=1,og=4,tim=26349629223153
BINDS #10(bad):
bind 0: dty=1 mxl=32(09) mal=00 scl=00 pre=00 oacflg=13
oacfl2=1 size=96 offset=0
bfp=ffffffff7c4b7c38 bln=32 avl=09 flg=05
value="104539-08"
bind 1: dty=1 mxl=32(09) mal=00 scl=00 pre=00 oacflg=13
oacfl2=1 size=0 offset=32
bfp=ffffffff7c4b7c58 bln=32 avl=09 flg=01
value="104539-08"
bind 2: dty=1 mxl=32(09) mal=00 scl=00 pre=00 oacflg=13
oacfl2=1 size=0 offset=64
bfp=ffffffff7c4b7c78 bln=32 avl=09 flg=01
value="104539-08"
BINDS #7(good):
bind 0: dty=1 mxl=32(09) mal=00 scl=00 pre=00 oacflg=13
oacfl2=1 size=96 offset=0
bfp=ffffffff7c4aeac0 bln=32 avl=09 flg=05
value="104539-08"
bind 1: dty=1 mxl=32(09) mal=00 scl=00 pre=00 oacflg=13
oacfl2=1 size=0 offset=32
bfp=ffffffff7c4aeae0 bln=32 avl=09 flg=01
value="104539-08"
bind 2: dty=1 mxl=32(09) mal=00 scl=00 pre=00 oacflg=13
oacfl2=1 size=0 offset=64
bfp=ffffffff7c4aeb00 bln=32 avl=09 flg=01
value="104539-08"
EXEC
#10(bad):c=0,e=619,p=0,cr=0,cu=0,mis=0,r=0,dep=1,og=4,tim=746385914651
EXEC
#7(good):c=0,e=496,p=0,cr=0,cu=0,mis=0,r=0,dep=1,og=4,tim=26349629224220
FETCH
#10(bad):c=110000,e=102469,p=0,cr=7698,cu=0,mis=0,r=1,dep=1,og=4,tim=7463860
17309
FETCH
#7(good):c=0,e=206,p=0,cr=16,cu=0,mis=0,r=1,dep=1,og=4,tim=26349629224499
FETCH
#10(bad):c=0,e=12,p=0,cr=0,cu=0,mis=0,r=1,dep=1,og=4,tim=746386017582
FETCH
#7(good):c=0,e=6,p=0,cr=0,cu=0,mis=0,r=1,dep=1,og=4,tim=26349629224619
FETCH
#10(bad):c=0,e=8,p=0,cr=0,cu=0,mis=0,r=1,dep=1,og=4,tim=746386017774
FETCH
#7(good):c=0,e=5,p=0,cr=0,cu=0,mis=0,r=1,dep=1,og=4,tim=26349629224734
FETCH
#10(bad):c=0,e=9,p=0,cr=0,cu=0,mis=0,r=1,dep=1,og=4,tim=746386017967
FETCH
#7(good):c=0,e=5,p=0,cr=0,cu=0,mis=0,r=1,dep=1,og=4,tim=26349629224849
FETCH
#10(bad):c=0,e=8,p=0,cr=0,cu=0,mis=0,r=1,dep=1,og=4,tim=746386018157
FETCH
#7(good):c=0,e=5,p=0,cr=0,cu=0,mis=0,r=1,dep=1,og=4,tim=26349629224961
FETCH
#10(bad):c=0,e=26,p=0,cr=0,cu=0,mis=0,r=0,dep=1,og=4,tim=746386018363
FETCH
#7(good):c=0,e=14,p=0,cr=0,cu=0,mis=0,r=0,dep=1,og=4,tim=26349629225081
BINDS #10(bad):
bind 0: dty=1 mxl=32(09) mal=00 scl=00 pre=00 oacflg=13
oacfl2=1 size=96 offset=0
bfp=ffffffff7c4b7c38 bln=32 avl=09 flg=05
value="104539-07"
bind 1: dty=1 mxl=32(09) mal=00 scl=00 pre=00 oacflg=13
oacfl2=1 size=0 offset=32
bfp=ffffffff7c4b7c58 bln=32 avl=09 flg=01
value="104539-07"
bind 2: dty=1 mxl=32(09) mal=00 scl=00 pre=00 oacflg=13
oacfl2=1 size=0 offset=64
bfp=ffffffff7c4b7c78 bln=32 avl=09 flg=01
value="104539-07"
BINDS #7(good):
bind 0: dty=1 mxl=32(09) mal=00 scl=00 pre=00 oacflg=13
oacfl2=1 size=96 offset=0
bfp=ffffffff7c4aeac0 bln=32 avl=09 flg=05
value="104539-07"
bind 1: dty=1 mxl=32(09) mal=00 scl=00 pre=00 oacflg=13
oacfl2=1 size=0 offset=32
bfp=ffffffff7c4aeae0 bln=32 avl=09 flg=01
value="104539-07"
bind 2: dty=1 mxl=32(09) mal=00 scl=00 pre=00 oacflg=13
oacfl2=1 size=0 offset=64
bfp=ffffffff7c4aeb00 bln=32 avl=09 flg=01
value="104539-07"
EXEC
#10(bad):c=0,e=684,p=0,cr=0,cu=0,mis=0,r=0,dep=1,og=4,tim=746386019967
EXEC
#7(good):c=0,e=463,p=0,cr=0,cu=0,mis=0,r=0,dep=1,og=4,tim=26349629226116
FETCH
#10(bad):c=100000,e=101693,p=0,cr=7697,cu=0,mis=0,r=1,dep=1,og=4,tim=7463861
21784
FETCH
#7(good):c=0,e=186,p=0,cr=16,cu=0,mis=0,r=1,dep=1,og=4,tim=26349629226374
FETCH
#10(bad):c=0,e=12,p=0,cr=0,cu=0,mis=0,r=1,dep=1,og=4,tim=746386122056
FETCH
#7(good):c=0,e=6,p=0,cr=0,cu=0,mis=0,r=1,dep=1,og=4,tim=26349629226492
FETCH
#10(bad):c=0,e=26,p=0,cr=0,cu=0,mis=0,r=0,dep=1,og=4,tim=746386122263
FETCH
#7(good):c=0,e=14,p=0,cr=0,cu=0,mis=0,r=0,dep=1,og=4,tim=26349629226615
BINDS #10(bad):
bind 0: dty=1 mxl=32(09) mal=00 scl=00 pre=00 oacflg=13
oacfl2=1 size=96 offset=0
bfp=ffffffff7c4b7c38 bln=32 avl=09 flg=05
value="107278-01"
bind 1: dty=1 mxl=32(09) mal=00 scl=00 pre=00 oacflg=13
oacfl2=1 size=0 offset=32
bfp=ffffffff7c4b7c58 bln=32 avl=09 flg=01
value="107278-01"
bind 2: dty=1 mxl=32(09) mal=00 scl=00 pre=00 oacflg=13
oacfl2=1 size=0 offset=64
bfp=ffffffff7c4b7c78 bln=32 avl=09 flg=01
value="107278-01"
BINDS #7(good):
bind 0: dty=1 mxl=32(09) mal=00 scl=00 pre=00 oacflg=13
oacfl2=1 size=96 offset=0
bfp=ffffffff7c4aeac0 bln=32 avl=09 flg=05
value="107278-01"
bind 1: dty=1 mxl=32(09) mal=00 scl=00 pre=00 oacflg=13
oacfl2=1 size=0 offset=32
bfp=ffffffff7c4aeae0 bln=32 avl=09 flg=01
value="107278-01"
bind 2: dty=1 mxl=32(09) mal=00 scl=00 pre=00 oacflg=13
oacfl2=1 size=0 offset=64
bfp=ffffffff7c4aeb00 bln=32 avl=09 flg=01
value="107278-01"
EXEC
#10(bad):c=0,e=686,p=0,cr=0,cu=0,mis=0,r=0,dep=1,og=4,tim=746386123823
EXEC
#7(good):c=0,e=466,p=0,cr=0,cu=0,mis=0,r=0,dep=1,og=4,tim=26349629227628
FETCH
#10(bad):c=200000,e=204295,p=0,cr=15358,cu=0,mis=0,r=1,dep=1,og=4,tim=746386
328243
FETCH
#7(good):c=0,e=143,p=0,cr=7,cu=0,mis=0,r=1,dep=1,og=4,tim=26349629227843
FETCH
#10(bad):c=0,e=37,p=0,cr=0,cu=0,mis=0,r=0,dep=1,og=4,tim=746386328513
FETCH
#7(good):c=0,e=13,p=0,cr=0,cu=0,mis=0,r=0,dep=1,og=4,tim=26349629227941
BINDS #10(bad):
bind 0: dty=1 mxl=32(09) mal=00 scl=00 pre=00 oacflg=13
oacfl2=1 size=96 offset=0
bfp=ffffffff7c4b7c38 bln=32 avl=09 flg=05
value="107366-01"
bind 1: dty=1 mxl=32(09) mal=00 scl=00 pre=00 oacflg=13
oacfl2=1 size=0 offset=32
bfp=ffffffff7c4b7c58 bln=32 avl=09 flg=01
value="107366-01"
bind 2: dty=1 mxl=32(09) mal=00 scl=00 pre=00 oacflg=13
oacfl2=1 size=0 offset=64
bfp=ffffffff7c4b7c78 bln=32 avl=09 flg=01
value="107366-01"
BINDS #7(good):
bind 0: dty=1 mxl=32(09) mal=00 scl=00 pre=00 oacflg=13
oacfl2=1 size=96 offset=0
bfp=ffffffff7c4aeac0 bln=32 avl=09 flg=05
value="107366-01"
bind 1: dty=1 mxl=32(09) mal=00 scl=00 pre=00 oacflg=13
oacfl2=1 size=0 offset=32
bfp=ffffffff7c4aeae0 bln=32 avl=09 flg=01
value="107366-01"
bind 2: dty=1 mxl=32(09) mal=00 scl=00 pre=00 oacflg=13
oacfl2=1 size=0 offset=64
bfp=ffffffff7c4aeb00 bln=32 avl=09 flg=01
value="107366-01"
EXEC
#10(bad):c=0,e=706,p=0,cr=0,cu=0,mis=0,r=0,dep=1,og=4,tim=746386330128
EXEC
#7(good):c=10000,e=493,p=0,cr=0,cu=0,mis=0,r=0,dep=1,og=4,tim=26349629228936
FETCH
#10(bad):c=210000,e=208902,p=0,cr=15673,cu=0,mis=0,r=1,dep=1,og=4,tim=746386
539152
FETCH
#7(good):c=0,e=121,p=0,cr=7,cu=0,mis=0,r=1,dep=1,og=4,tim=26349629229130
FETCH
#10(bad):c=0,e=35,p=0,cr=0,cu=0,mis=0,r=0,dep=1,og=4,tim=746386539431
FETCH
#7(good):c=0,e=12,p=0,cr=0,cu=0,mis=0,r=0,dep=1,og=4,tim=26349629229225
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