Oracle 10g Performance: chapter 07 io

IO Waits

Kyle Hailey
Kyle.hailey@embarcadero.com
http://oraclemonitor.com

Waits Covered in this Section

1. db file sequential read
2. db file scattered read Buffer Cache I/O
3. db file parallel read
4. read by other session
5. direct path read
6. direct path write
7. direct path read temp
8. direct path write temp PGA I/O
9. direct path write (lob)
10. Local write wait
11. data file init write Special Cases

Copyright 2006 Kyle Hailey

IO Waits
SGA
Log Library Buffer
Buffer Cache Cache

User1 DBWR

Data Files

Standard Table/Index IO

1. db file sequential read
 Single block read

1. db file scattered read
 Multi block read

1. db file parallel read
 Non-contiguous multi block read

1. read by other session
 Wait for another session to do the io


db file sequential read
Buffer Cache  The top wait
 Single Block Read
 Data via Index and/or Rowid
 Rollback (if expecting FTS => problem)

Select **from emp where empno = 9999;
Select from emp where empno = 9999;
Shadow Index on emp.empno
Process

1) Search Buffer Cache for
the block by rowid
2) Fails Note: “sequential” means
3) Reads of disk A sequence like a
• File rowid
• Block


db file scattered read
 Multi Block Read
Buffer Cache  FullTable Scan
 Index Fast Full Scans

SQL> select * from emp;
SQL> select * from emp;
Shadow
Process
1) Search Buffer Cache for the
blocks Note: Scattered Means
2) Fails
Blocks are read and
3) Reads off disk
• File scattered throughout
• Block buffer cache
• Multi Block Read Count

db_file_multiblock_read_count

db file parallel read

Buffer Cache  Process issues multiple single block reads in parallel
 Documentation says only for recovery
 But seems to happen for normal read ops
 Async Call – wait for all reads to complete

 Examples
 Not contiguous multi block read
 Index full or range scan
Shadow
 Where values in Select **from emp where
Process Select from emp where
Empno in (1,2,3,4,5,6);
Empno in (1,2,3,4,5,6);

1) Search Buffer Cache for
the blocks
2) Fails
3) Reads that block off Disk

Read by other Session
Buffer Cache

Multiple sessions reading the
same data that requires IO
Ex) two users doing a full table
scan at the same time

S1 S2
1. Block not found in cache
2. Read block from disk
3. Found other session already
reading block from disk
4. Wait for the other session to finish
IO


IO – Further Investigation
select parameter1, parameter2, parameter3 from v$event_name

NAME P1 P2 P3
read by other session file# block# class#
db file sequential read file# block# blocks
db file scattered read file# block# blocks
db file parallel read files blocks requests

P1 and P2 are file# , block#
We can use P1, P2, P3 from ASH to get more info

Exception:
db file parallel read – p1,p2,p3 not useful

sequential reads – blocks read
select
event,
ash.p3,
o.object_name objn,
o.object_type otype,
CURRENT_FILE# filen,
CURRENT_BLOCK# blockn,
ash.SQL_ID
from v$active_session_history ash,
all_objects o
where event like 'db file sequential read'
and o.object_id (+)= ash.CURRENT_OBJ#
order by sample_time; P3= # of
blocks
EVENT P3 OBJN OTYPE FILEN BLOCKN SQL_ID
db file sequential read 1 49890 MGMT_METRICS_1HOUR_ INDEX 3 41737
db file sequential read 1 50908 MGMT_DB_SGA_ECM TABLE 3 28489 35at43xqj7bs0
db file sequential read 1 55303 TOTO TABLE 1 60218 7xftj55rvjw9s


scattered reads – multi blocks read

select
event,
ash.p3,
o.object_name objn,
CURRENT_FILE# filen,
ash.SQL_ID
all_objects o
where event like 'db file scattered read'
and o.object_id (+)= ash.CURRENT_OBJ# P3= # of
order by sample_time; blocks
EVENT P3 OBJN OTYPE FILEN BLOCKN SQL_ID
db file scattered read 8 9078 WRH$_SYSMETRIC_HISTO TABLE 3 52363
db file scattered read 5 8781 WRI$_ALERT_HISTORY TABLE 3 2676
db file scattered read 8 57 OBJAUTH$ TABLE 1 33993 3t2mk1prj24hu


IO by File
select io.cnt,
round(io.cnt/(&v_minutes*60),2) aas,
io.event,
io.p1 p1,
f.tablespace_name
from ( select
count(*) cnt,
substr(event,0,25) event,
ash.p1 p1
from v$active_session_history ash
where ( event like 'db file s%' or event like 'direct%' )
and sample_time > sysdate - &v_minutes/(60*24)
group by
event ,
ash.p1
) io,
dba_data_files f CNT AAS EVENT P1 TABLESPACE
where 1 .00 db file sequential read 1 SYSTEM
f.file_id = io.p1 2 .00 db file sequential read 3 SYSAUX
Order by io.cnt ; 38 .06 db file sequential read 6 SOE
179 .30 db file sequential read 7 SOEINDEX

IO by Object
select
count(*) cnt,
CURRENT_OBJ#||' '||o.object_name objn,
o.object_type otype
all_objects o
and sample_time > sysdate - &1/(60*24)
and session_state='WAITING'
group by
CURRENT_OBJ#, o.object_name ,
o.object_type
Order by count(*)

CNT AAS OBJN OTYPE

PARTITION.00
79 52949 ORDER_ITEMS TABLE
97 .00 -1
130 .00 53117 ORD_STATUS_IX INDEX
498 .01 53120 CUST_EMAIL_IX INDEX
512 .01 0
1632 .03 53112 ITEM_ORDER_IX INDEX

IO by SQL
select
round(sum(cnt) over ( partition by io.sql_id order by sql_id ) / (&v_minutes*60),2) aas,
io.sql_id,
io.cnt cnt,
100*cnt/sum(cnt) over ( partition by io.sql_id order by sql_id ) pct,
o.object_name obj,
o.subobject_name sub_obj,
substr(io.event,8,10) event,
AAS SQL_ID % OBJ TABLESPACE
io.p1 file#, ----- ------------- --- --------------- ----------
f.tablespace_name tablespace_name,
tbs.contents .18 0yas01u2p9ch4 6 ITEM_PRODUCT_IX SOEINDEX
from
(
6 ORDER_ITEMS_UK SOEINDEX
select 88 ITEM_ORDER_IX SOEINDEX
sql_id,
event,
.32 6v6gm0fd1rgrz 6 WAIT_OBJECTS SYSTEM
count(*) cnt, 94 UNDO UNDOTBS1
count(*) / (&v_minutes*60) aas,
CURRENT_OBJ# ,
ash.p1
from v$active_session_history ash
and sample_time > sysdate - &v_minutes/(60*24)
group by
CURRENT_OBJ#,
event,
ash.p1,
sql_id
) io,
dba_data_files f
,all_objects o
, dba_tablespaces tbs
where
f.file_id = io.p1
and o.object_id (+)= io.CURRENT_OBJ#
and tbs.tablespace_name= f.tablespace_name
Order by tcnt, sql_id, cnt
/

Missing Object IDs
 dba_extents – get object name
select segment_name,
select segment_name,
segment_type
segment_type
from dba_extents
from dba_extents
where file_id = P1
where file_id = P1
and P2 between
and P2 between
block_id and block_id + blocks – 1;
block_id and block_id + blocks – 1;
 Dba_extents is notoriously slow
 Options
 Create a table as select – use table
 recreate as object extents change
 Catch blocks in x$bh when waits occur


Copy of dba_extents
Enter value for file: 3
Enter value for block: 6619
OWNER SEGMENT_NAME SEGMENT_TYPE
WMSYS LOG_TAB_PK INDEX

Elapsed: 00:00:41.25

create table myextents as select * from dba_extents
Table created.

Elapsed: 00:01:25.73

CNT OWN SEGMENT_NAME SEGMENT_TYPE
11 SYS SMON_SCN_TO_TIME CLUSTER
993 SYS _SYSSMU7$ TYPE2 UNDO
150 rows selected.

Elapsed: 00:00:01.03

IO Solutions

1. Check average read times per file
 Should be between 5-20 ms
 Data in Statspack under “File IO Stats”
1. Check Cache buffer Hit ratio
 Check db_cache_advice 9i and higher
 Data in Statspack under “Buffer Pool Advisory”
 Want to optimize data caching
1. Tune High IO SQL
 Check reads off of UNDO


Step 1a: Ave Read Time
File IO Stats DB/Inst:labsf03 Snaps: 1-2
File IO Stats DB/Inst:labsf03 Snaps: 1-2
Tablespace
Tablespace Filename
Filename
------------------------ ----------------------------------------------------
------------------------ ----------------------------------------------------
Av
Av MxMx
Av
Av
Av
Av Rd
Rd RdRd Av
Av Av
Av Buffer BufWt
Buffer BufWt
Reads Reads/s (ms) Bkt Blks/Rd
Reads Reads/s (ms) Bkt Blks/Rd Writes Writes/s
Writes Writes/s Waits (ms)
Waits (ms)
---------- ---- ------- ----- --- ------- ------------ -------- ---------- --
---------- ---- ------- ----- --- ------- ------------ -------- ---------- --
SYSTEM
SYSTEM /u01/app/oracle/oradata/labsf03/system01.dbf
/u01/app/oracle/oradata/labsf03/system01.dbf
445
445 15
15 0.4 16
0.4 16 1.0
1.0 1,157
1,157 39
39 2,744
2,744 93.3
93.3
USERS
USERS /u01/app/oracle/oradata/labsf03/users01.dbf
/u01/app/oracle/oradata/labsf03/users01.dbf
223
223 77 0.5 ###
0.5 ### 1.0
1.0 9,725
9,725 324
324 44 100.0
100.0

IO should be under 20ms
Fastest possible is around 7ms
Faster speeds are due to read caching

Step 1b: Ave Read Time
select
select
to_char(begin_interval_time,'yyyy-mm-dd hh24:mi') snap_time,
to_char(begin_interval_time,'yyyy-mm-dd hh24:mi') snap_time,
file#, readtim/nullif(phyrds,0) avg_read_ms, phyrds
file#, readtim/nullif(phyrds,0) avg_read_ms, phyrds
from
from SNAP_TIME FILE# AVG_READ_MS PHYRDS
SNAP_TIME FILE# AVG_READ_MS PHYRDS
DBA_HIST_FILESTATXS f, 2008-01-05 12:00
DBA_HIST_FILESTATXS f, 2008-01-05 12:00 99 36.67 39
36.67 39
dba_hist_snapshot ss
dba_hist_snapshot 2008-01-05 12:00
2008-01-05 12:00 10
10 32.31
32.31 39
39
2008-01-05 13:00
2008-01-05 13:00 11 11.63
11.63 178224
178224
where f.snap_id=s.snap_id ; ; 2008-01-05 13:00
where f.snap_id=s.snap_id
2008-01-05 13:00 22 56.37
56.37 2014
2014
2008-01-05 13:00
2008-01-05 13:00 33 17.38
17.38 50668
50668
2008-01-05 13:00
2008-01-05 13:00 44 9.39
9.39 565321
565321
2008-01-05 13:00
2008-01-05 13:00 55 38.78
38.78 41
41
2008-01-05 13:00
2008-01-05 13:00 66 28.29
28.29 41
41
2008-01-05 13:00
2008-01-05 13:00 77 27.44
27.44 39
39
2008-01-05 13:00
2008-01-05 13:00 88 42.56
42.56 39
39
2008-01-05 13:00
2008-01-05 13:00 99 36.67
36.67 39
39
2008-01-05 13:00
2008-01-05 13:00 10
10 32.31
32.31 39
39

Step 1c: Ave Read Time
select
select
to_char(begin_time,'yyyy-mm-dd hh24:mi') begin_time,
to_char(begin_time,'yyyy-mm-dd hh24:mi') begin_time,
file_id fid,
file_id fid,
average_read_time *10 avgrd_ms,
average_read_time *10 avgrd_ms,
average_write_time *10 avgwr_ms,
average_write_time *10 avgwr_ms,
physical_reads pr,
physical_reads pr,
physical_writes pw
physical_writes pw BEGIN_TIME FID AVGRD_MS AVGWR_MS PR PW
from
from
BEGIN_TIME FID AVGRD_MS AVGWR_MS PR PW
---------------- ---- -------- -------- ---------- ----------
---------------- ---- -------- -------- ---------- ----------
V$FILEMETRIC_HISTORY ff 2008-01-30 12:25 11
V$FILEMETRIC_HISTORY
2008-01-30 12:25 5.2
5.2
2.5
2.5
100
100
24
24
2008-01-30 12:25 5 80.0 20.0 2 2
order by begin_time;
order by begin_time;
2008-01-30 12:25
2008-01-30 12:25 2
5 80.0
36.7
20.0
2.0 3
2
218
2
2008-01-30 12:25 2 36.7 2.0 3 218
2008-01-30 12:25 4 22.8 1.8 89 2754
2008-01-30 12:25 4 22.8 1.8 89 2754
2008-01-30 12:25 3 22.9 2.6 14 47
2008-01-30 12:25 3 22.9 2.6 14 47


Step1 & OEM
 ADDM advisory expects I/Os to be under 10ms
 Can change the behavior with

exec DBMS_ADVISOR.SET_DEFAULT_TASK_PARAMETER(
'ADDM',
'DBIO_EXPECTED',
<new value>);

Step 2 : Buffer Pool Advisory

Buffer Pool Advisory
Buffer Pool Advisory Buffers for
Size for
Size for Size
Size Buffers for Read
Read Estimated
Estimated
PP Est (M) Factor
Est (M) Factor Estimate
Estimate Factor
Factor Physical Reads
Physical Reads
--- -------- ------ ------------
--- -------- ------ ------------ ------
------ --------------
--------------
DD 56
56 .1
.1 6,986
6,986 2.3
2.3 58,928
58,928
DD 112
112 .2
.2 13,972
13,972 1.6
1.6 42,043
42,043
DD 224
224 .4
.4 27,944
27,944 1.0
1.0 25,772
25,772
DD 336
336 .6
.6 41,916
41,916 1.0
1.0 25,715
25,715
DD 448
448 .8
.8 55,888
55,888 1.0
1.0 25,715
25,715
DD 596
596 1.0
1.0 74,351
74,351 1.0
1.0 25,715
25,715
DD 728
728 1.2
1.2 90,818
90,818 1.0
1.0 25,715
25,715
DD 840
840 1.4
1.4 104,790
104,790 1.0
1.0 25,715
25,715
DD 952
952 1.6
1.6 118,762
118,762 1.0
1.0 25,715
25,715
DD 1,064
1,064 1.8
1.8 132,734
132,734 1.0
1.0 25,715
25,715


Step 3: Find Top I/O SQL
select count(*),sql_id, event
select count(*),sql_id, event
from v$active_session_history
from v$active_session_history
where event in ('db file sequential read',
where event in ('db file sequential read',
'db file scattered read',
'db file scattered read',
'db file parallel read')
'db file parallel read')
group by sql_id, event
group by sql_id, event
order by count(*);
order by count(*);
COUNT(*) SQL_ID
COUNT(*) SQL_ID EVENT
EVENT
10 8hk7xvhua40va db file sequential read
10 8hk7xvhua40va db file sequential read
335 3hatpjzrqvfn7 db file sequential read
335 3hatpjzrqvfn7 db file sequential read
343 0uuqgjq7k12nf db file sequential read
343 0uuqgjq7k12nf db file sequential read
549 75621g9y3xmvd db file sequential read
549 75621g9y3xmvd db file sequential read
1311 0bzhqhhj9mpaa db file sequential read
1311 0bzhqhhj9mpaa db file sequential read
1523 41zu158rqf4kf db file sequential read
1523 41zu158rqf4kf db file sequential read
1757 0yas01u2p9ch4 db file sequential read
1757 0yas01u2p9ch4 db file sequential read


Step 3: OEM find top SQL


IO Configuration Issues
 Unix Buffer Cache
 Disk Spindles Machine Memory
 Raid 5 Unix File Not
Unix File Physical IO SGA
Cache

Physical IO

If average IO read times
are under 7ms them
probably coming from Unix
File Cache

IO Throughput
One Disk 74G – Few IOPS 92 IO/sec

37 Disks 2G – Many IOPS 1887 IO/sec


Disk 2Gb vs 70GB
Seagate Seagate
Barracuda 4LP Cheetah 73LP
Capacity 2.16GB 73.4GB
Rotation Speed 7200rpm 10000rpm
Rotational Delay(avg) 4.1ms 3ms
Time to read 32Kb 6ms 3ms
Seek Time (avg) 9.4ms 4.9
Total time for Single I/O 19.5ms 10.9ms
I/O per second 51 92
(conservative)
IOPs/sec per 100GB 2550 126
James Morle http://scaleability.com


Raid 5
http://www.miracleas.com/BAARF/BAARF2.html
P1 P2
Readers on different
B – Battle disks run without conflict
A – Against
A – Any
P2
R – Raid Writes require two reads
F - Five plus a write – read data,
read parity then write
Reads can conflict on
P1
smaller stripe sizes 32K
or 64K

Raid Levels
Raid Level none 0 0+1 5
(stripe) (striped then
mirrored)

Control file 2 1 1 3
Redo log 4 1 1 3
System tablespace 2 1 1 3
Sort segment 4 1 1 3
Rollback segment 2 1 1 5
Index read only 2 1 1 1
Sequential read only 4 1 1 3
DBWR intensive files 1 1 1 5
Direct load intensive 4 1 1 3
Data protection 4 5 1 2
Operating costs 1 1 5 3

http://www.miracleas.com/BAARF/1.Millsap2000.01.03-RAID5.pdf

Direct I/O WAITS
Direct I/O :
This mechanism lets the client bypass the buffer cache for
I/O intensive operations.
The disk blocks are written into and read from process
private memory.
 direct path read :
 Parallel Query
 direct path write
 sqlldr
 loading/reading LOBs
 parallel DMLs
 create table as select
 create index
 direct path read temp , direct path write temp
 Sorting


Direct IO

Shadow
Process

PGA
Sort Area Buffer Cache
Direct Path
PQO Reads

X


direct path read
Buffer Cache

 Parallel Query
 See v$px_session

X select parameter1, parameter2, parameter3
from v$event_name
where name='direct path read';
Shadow PARAMETER1 PARAMETER2 PARAMETER3
Process
file number first dba block cnt
PGA
PQO

_serial_direct_read = true


Further Investigation ASH
select
select
session_id sid,
session_id sid,
QC_SESSION_ID qsid,
QC_SESSION_ID qsid,
ash.p3,
ash.p3,
CURRENT_FILE# fn,
CURRENT_FILE# fn,
ash.SQL_ID
ash.SQL_ID
all_objects o
all_objects o
where event like 'direct path read'
where event like 'direct path read'
Order by sample_time;
Order by sample_time;
SID QSID P3 OBJN OTYPE FN BLOCKN SQL_ID
SID QSID P3 OBJN OTYPE FN BLOCKN SQL_ID
--- ---- -- ----- ------ -- ------ -------------
--- ---- -- ----- ------ -- ------ -------------
149 152 8 TOTO TABLE
149 152 8 TOTO TABLE 1 194072 4gp8tg0b2s722
1 194072 4gp8tg0b2s722
1 192304 4gp8tg0b2s722
60 152 8 TOTO TABLE
1 190592 4gp8tg0b2s722
54 152 6 TOTO TABLE
1 201274 4gp8tg0b2s722
1 198552 4gp8tg0b2s722


PQO - ASH
select
ash.SQL_ID,
QC_SESSION_ID qsid,
count(*) cnt,
count (distinct session_id) deg,
nvl(o.object_name,to_char(CURRENT_OBJ#)) obj,
decode(session_state, 'WAITING',event,'CPU') event
all_objects o
where o.object_id (+)= ash.CURRENT_OBJ#
and qc_session_id is not null
SQL_ID QSID CNT DEG OBJ OTYPE EVENT
group by qc_session_id, sql_id, o.object_name,
7p3jt75phub2d 144 386 4 WAIT_OBJECTS TABLE PX Deq Credit: send blkd
o.object_type, CURRENT_OBJ#, event, session_stateTABLE
144 4 3 WAIT_OBJECTS PX qref latch
Order by qc_session_id, sql_id144 37 1 WAIT_OBJECTS TABLE db file sequential read
144 3 2 WAIT_OBJECTS TABLE direct path read
144 70 1 WAIT_OBJECTS TABLE CPU
144 21 4 0 PX Deq Credit: send blkd
144 12 4 0 db file sequential read

direct path write
 Occurs when:
 insert /*+ APPEND */
 sql*loader direct=y
 Create table as select
 Loading LOBS
 Parallel insert
Buffer Cache
 Create index

Shadow select parameter1, parameter2, parameter3
Process from v$event_name
where name='direct path write';
DBWR
PGA PARAMETER1 PARAMETER2 PARAMETER3

Seems to be a bug on 10g where
direct path write waits are
DATA incorrectly recorded as CPU


Direct Path Read Temp
Direct Path Write Temp
select parameter1, parameter2, parameter3
 Sorting from v$event_name
where name in ('direct path write temp‘,
 Write to Temp ‘direct path read temp’);
PARAMETER1 PARAMETER2 PARAMETER3
 Read from Temp

Shadow
Process

PGA

TEMP DATA
Buffer Cache


Direct Path Read Temp
Direct Path Write Temp
This event happens when sorting overflows the memory buffers and has to be
written to disk. If it's a problem consider increasing parameter

pga_aggregate_target
The explain plan can give estimated sort size requirements and extended row
source stats in the explain plan can give the actual sort size usage of the SQL
statement
Buffer Cache

Shadow
Process select s.sid, s. process,
s.sql_id, SID SQL_ID SEGTYPE MB TABLESPACE
tmp.segtype, --- ------------- ------- -- ----------
((tmp.blocks*8)/1024) MB, 90 gm5s0vc0vzppc SORT 2 TEMP03
PGA from
tmp.tablespace
105 gm5s0vc0vzppc SORT 2 TEMP03
v$tempseg_usage tmp, 80 gm5s0vc0vzppc SORT 2 TEMP03
v$session s 105 gm5s0vc0vzppc HASH 2 TEMP03
where tmp.session_num=s.serial# 102 gm5s0vc0vzppc SORT 2 TEMP03
and segtype in ('HASH','SORT') 90 gm5s0vc0vzppc HASH 2 TEMP03
order by blocks desc

TEMP DATA


PGA Aggregate Target
Manual override broken 10.2.0.3 fixed in 11.1.0.7
alter session set workarea_size_policy = manual;
alter session set sort_area_size = 104857600;
Workaround, run command twice
But doesn’t work for parallel connections that still fall back
on default which is 64K unless otherwise specified
HASH_AREA_SIZE seems unaffected by problem

9i, a single sessions maximum sort area using PGA_AGGREGATE_TARGET was fixed to
100M unless setting
_pga_max_size: Maximum PGA size for a single process
Defaults to 200M
_smm_max_size: Maximum workarea size for one process , defined in KILO BYTES
Defaults Min(0.05*pga_aggregate_target,0.5*_pga_max_size,100M)

In 10.2 max sort size is 10% of PGA_AGGREGATE_TARGET
(100M applies as long as pga_aggregate_target is smaller than 1GB)
example : pga_aggregate_target set to 5GB
_smm_max_size of 500MB (was 100MB )
_pga_max_size of 1000MB (was 200MB).

Data file init write

 When autoextend is set and many extensions are
happening
 Can be the root cause of other waits
 Enq: TX - contention


Local Write Wait
 Truncating a table
 Wait for Data Cache to be cleared of all blocks of
truncated table
 Wait by shadow for DBWR

 If a problem try
 GTT
 (reduce db cache size , not usually an option)


Further Investigation
select * from v$event_name
where name = ‘local write wait'
NAME
NAME P1
P1 P2
P2 P3
P3
local write wait file# block#
local write wait file# block#

select
ash.p1,ash.p2, ash.SQL_ID, count(*)
from v$ash ash
where event='local write wait'
group by P1 P2 SQL_ID COUNT

ash.p1,ash.p2, ash.SQL_ID; 201 2 0q8k9xfmz0k2k 194
201 5 0q8k9xfmz0k2k 34
201 6 0q8k9xfmz0k2k 9
201 4 0q8k9xfmz0k2k 10

Temporary File #’s
SQL> select file# from v$datafile;
FILE#
1 Wait Temporary File#’s =
2 Db_files + file#
3
4 SQL> show parameters db_files
5 NAME VALUE
6
7 db_files 200
8
SQL> select file# from v$tempfile;
FILE#
2 File# 201 = v$tempfile 1
1

Local Write Wait:extent allocation

CREATE TEMPORARY TABLESPACE "NEWTEMP"
TEMPFILE '/d3/temp01.dbf' SIZE 100M
AUTOEXTEND ON
EXTENT MANAGEMENT LOCAL UNIFORM SIZE 64K;

ALTER DATABASE DEFAULT
TEMPORARY TABLESPACE newtemp;

select a.*, b.*
from dba_objects a, dba_objects b
order by a.owner

Local Write Waits


Local Write Wait: Solutions
 Truncating a table
 Use GTT
 ( reduce size of buffer cache – unlikely)

 Temporary Table Space Allocations
 Increase extent size


Summary I/O
 Buffer Cache IO
 db file sequential read
 db file scattered read
 db file parallel read

 Tune
 I/O’s
should be < 10 ms
 Check Buffer Cache Advisory
 Tune SQL


Summary Direct I/O and Other
 direct path read
 PQO
 direct path write
 direct path operations
 direct path read temp / direct path write temp
 sorts
 direct path write (lob)
 stored NOCACHE
 local write wait –
 Temp extensions
 Truncates
 data file init write – data file extension


Oracle 10g Performance: chapter 07 io

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