IO Waits Kyle Hailey

#.2 Copyright 2006 Kyle Hailey Waits Covered in this Section 1.db file sequential read 2.db file scattered read 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 9.direct path write (lob) 10.file open 11.file identify 12.Local write wait 13.data file init write 14.sort segment request Standard I/O Direct I/O Special Cases

#.3 Copyright 2006 Kyle Hailey Buffer Cache REDO Lib Cache Buffer Cache Locks Network I/O

#.4 Copyright 2006 Kyle Hailey IO Waits Data Files DBWR Buffer Cache User1 SGA Library Cache Log Buffer

#.5 Copyright 2006 Kyle Hailey Standard Table/Index IO 1.db file sequential read  Single block read 2.db file scattered read  Multi block read 3.db file parallel read  Non-contiguous multi block read 4.read by other session  Wait for another session to do the io

#.6 Copyright 2006 Kyle Hailey db file sequential read ShadowProcess 1) 1)Search Buffer Cache for the block by rowid 2) 2)Fails 3) 3)Reads of disk File Block Buffer Cache   The top wait   Single Block Read   Data via Index and/or Rowid   Rollback Select * from emp where empno = 9999; Note: “sequential” means A sequence like a rowid Index on emp.empno

#.7 Copyright 2006 Kyle Hailey db file scattered readShadowProcess 1) 1)Search Buffer Cache for the blocks 2) 2)Fails 3) 3)Reads off disk File Block Multi Block Read Count Buffer Cache   Multi Block Read   Full Table Scan   Index Fast Full Scans SQL> select * from all_objects; Note: Scattered Means Blocks are read and scattered throughout buffer cache

#.8 Copyright 2006 Kyle Hailey db file parallel read Shadow Process 1) 1)Search Buffer Cache for the blocks 2) 2)Fails 3) 3)Reads that block off Disk 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   Where values in Select * from emp where Empno in (1,2,3,4,5,6); Select * from emp where Empno in (1,2,3,4,5,6);

#.9 Copyright 2006 Kyle Hailey Read by other Session 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 S1 Buffer Cache S2 Multiple sessions reading the same data that requires IO Ex) to users doing a full table scan at the same time

#.10 Copyright 2006 Kyle Hailey Db file Sequential Read: Statspack Top 5 Timed Events ~~~~~~~~~~~~~~~~~~ % Total Event Waits Time (s) Ela Time db file scattered read 7, CPU time db file sequential read control file sequential read control file parallel write Top 5 Timed Events ~~~~~~~~~~~~~~~~~~ % Total Event Waits Time (s) Ela Time db file scattered read 7, CPU time db file sequential read control file sequential read control file parallel write What SQL ? What Object ?

#.11 Copyright 2006 Kyle Hailey Db file sequential read

#.12 Copyright 2006 Kyle Hailey db file scattered Read

#.13 Copyright 2006 Kyle Hailey Read by other session

#.14 Copyright 2006 Kyle Hailey IO – Further Investigation select parameter1, parameter2, parameter3 from v$event_name NAME P1 P2 P read by other session file# block# class# db file sequential read file# block# blocks db file scattered read file# block# blocks direct path read file number first dba block cnt direct path read temp file number first dba block cnt direct path write file number first dba block cnt direct path write temp file number first dba block cnt db file parallel read files blocks requests P1 and P2 are the same, file#, block# We can use P1, P2, P3 from ASH to get more info Exception: db file parallel read – p1,p2,p3 not useful

#.15 Copyright 2006 Kyle Hailey ASH – sequential reads select event, event, ash.p3, ash.p3, o.object_name objn, o.object_name objn, o.object_type otype, o.object_type otype, CURRENT_FILE# filen, CURRENT_FILE# filen, CURRENT_BLOCK# blockn, CURRENT_BLOCK# blockn, ash.SQL_ID ash.SQL_ID from v$active_session_history ash, all_objects o all_objects o where event like 'db file sequential read' and o.object_id (+)= ash.CURRENT_OBJ# and o.object_id (+)= ash.CURRENT_OBJ# order by sample_time; EVENT P3 OBJN OTYPE FILEN BLOCKN SQL_ID db file sequential read MGMT_METRICS_1HOUR_ INDEX db file sequential read MGMT_DB_SGA_ECM TABLE at43xqj7bs0 db file sequential read TOTO TABLE xftj55rvjw9s

#.16 Copyright 2006 Kyle Hailey ASH – scattered reads select event, event, ash.p3, ash.p3, o.object_name objn, o.object_name objn, o.object_type otype, o.object_type otype, CURRENT_FILE# filen, CURRENT_FILE# filen, CURRENT_BLOCK# blockn, CURRENT_BLOCK# blockn, ash.SQL_ID ash.SQL_ID from v$active_session_history ash, all_objects o all_objects o where event like 'db file scattered read' and o.object_id (+)= ash.CURRENT_OBJ# and o.object_id (+)= ash.CURRENT_OBJ# order by sample_time; EVENT P3 OBJN OTYPE FILEN BLOCKN SQL_ID db file scattered read WRH$_SYSMETRIC_HISTO TABLE db file scattered read WRI$_ALERT_HISTORY TABLE db file scattered read 8 57 OBJAUTH$ TABLE t2mk1prj24hu

#.17 IO by TBS & File select io.cnt, round(io.cnt/(&v_minutes*60),2) aas, round(io.cnt/(&v_minutes*60),2) aas, io.event, io.event, io.p1 p1, io.p1 p1, f.tablespace_name f.tablespace_name from ( select count(*) cnt, count(*) cnt, substr(event,0,25) event, substr(event,0,25) event, ash.p1 p1 ash.p1 p1 from v$active_session_history ash from v$active_session_history ash where ( event like 'db file s%' or event like 'direct%' ) where ( event like 'db file s%' or event like 'direct%' ) and sample_time > sysdate - &v_minutes/(60*24) and sample_time > sysdate - &v_minutes/(60*24) group by group by event, event, ash.p1 ash.p1 ) io, ) io, dba_data_files f dba_data_files fwhere f.file_id = io.p1 f.file_id = io.p1 Order by io.cnt ; CNT AAS EVENT P1 TABLESPACE CNT AAS EVENT P1 TABLESPACE db file sequential read 1 SYSTEM 1.00 db file sequential read 1 SYSTEM 2.00 db file sequential read 3 SYSAUX 2.00 db file sequential read 3 SYSAUX db file sequential read 6 SOE db file sequential read 6 SOE db file sequential read 7 SOEINDEX db file sequential read 7 SOEINDEX

#.18 IO by Objectselect count(*) cnt, count(*) cnt, CURRENT_OBJ#||' '||o.object_name objn, CURRENT_OBJ#||' '||o.object_name objn, o.object_type otype o.object_type otype from v$active_session_history ash, all_objects o all_objects o where ( event like 'db file s%' or event like 'direct%' ) and o.object_id (+)= ash.CURRENT_OBJ# and o.object_id (+)= ash.CURRENT_OBJ# and sample_time > sysdate - &1/(60*24) and sample_time > sysdate - &1/(60*24) and session_state='WAITING' and session_state='WAITING' group by CURRENT_OBJ#, o.object_name, CURRENT_OBJ#, o.object_name, o.object_type o.object_type Order by count(*) CNT AAS OBJN OTYPE CNT AAS OBJN OTYPE ORDER_ITEMS TABLE PARTITION ORDER_ITEMS TABLE PARTITION ORD_STATUS_IX INDEX ORD_STATUS_IX INDEX CUST_ _IX INDEX CUST_ _IX INDEX ITEM_ORDER_IX INDEX

#.19 IO by Object/tbs/wait Select io.cnt cnt, io.aas aas, io.aas aas, io.event event, io.event event, substr(io.obj,1,20) obj, substr(io.obj,1,20) obj, io.p1 p1, io.p1 p1, f.tablespace_name tablespace_name f.tablespace_name tablespace_name from ( select count(*) cnt, count(*) cnt, round(count(*)/(&v_minutes*60),2) aas, round(count(*)/(&v_minutes*60),2) aas, substr(event,0,15) event, substr(event,0,15) event, nvl(o.object_name,decode(CURRENT_OBJ#,-1,0,CURRENT_OBJ#)) obj, nvl(o.object_name,decode(CURRENT_OBJ#,-1,0,CURRENT_OBJ#)) obj, ash.p1, ash.p1, o.object_type otype o.object_type otype from v$active_session_history ash, from v$active_session_history ash, all_objects o all_objects o where ( event like 'db file s%' or event like 'direct%' ) where ( event like 'db file s%' or event like 'direct%' ) and o.object_id (+)= ash.CURRENT_OBJ# and o.object_id (+)= ash.CURRENT_OBJ# and sample_time > sysdate - &v_minutes/(60*24) and sample_time > sysdate - &v_minutes/(60*24) group by group by substr(event,0,15), substr(event,0,15), CURRENT_OBJ#, o.object_name, CURRENT_OBJ#, o.object_name, o.object_type, o.object_type, ash.p1 ) io, ash.p1 ) io, dba_data_files f dba_data_files f where f.file_id = io.p1 Order by io.cnt; CNT AAS EVENT OBJ P1 TABLESPACE_NAME db file sequent ORDER_ITEMS_PK 7 SOEINDEX 1.02 db file sequent ORDER_ITEMS_PK 7 SOEINDEX 1.02 db file sequent 0 3 SYSAUX 1.02 db file sequent 0 3 SYSAUX 2.03 db file scatter WAIT_OBJECTS 1 SYSTEM 2.03 db file scatter WAIT_OBJECTS 1 SYSTEM 2.03 db file sequent ORDER_ITEMS 6 SOE 2.03 db file sequent ORDER_ITEMS 6 SOE 3.05 db file sequent CUST_ _IX 7 SOEINDEX 3.05 db file sequent CUST_ _IX 7 SOEINDEX 4.07 db file sequent CUST_LNAME_IX 7 SOEINDEX 4.07 db file sequent CUST_LNAME_IX 7 SOEINDEX 6.10 db file sequent ORD_ORDER_DATE_IX 7 SOEINDEX 6.10 db file sequent ORD_ORDER_DATE_IX 7 SOEINDEX db file sequent ITEM_ORDER_IX 7 SOEINDEX db file sequent ITEM_ORDER_IX 7 SOEINDEX db file sequent 0 2 UNDOTBS db file sequent 0 2 UNDOTBS1

#.20 IO by SQLselect sum(cnt) over ( partition by io.sql_id order by sql_id ) tcnt, sum(cnt) over ( partition by io.sql_id order by sql_id ) tcnt, io.sql_id, io.sql_id, io.cnt cnt, io.cnt cnt, io.aas aas, io.aas aas, io.objn objn, io.objn objn, io.obj obj, io.obj obj, io.p1 p1, io.p1 p1, f.tablespace_name tablespace_name f.tablespace_name tablespace_namefrom( select select sql_id, sql_id, count(*) cnt, count(*) cnt, round(count(*)/(&v_minutes*60),2) aas, round(count(*)/(&v_minutes*60),2) aas, CURRENT_OBJ# objn, CURRENT_OBJ# objn, nvl(o.object_name,decode(CURRENT_OBJ#,-1,0,CURRENT_OBJ#)) obj, nvl(o.object_name,decode(CURRENT_OBJ#,-1,0,CURRENT_OBJ#)) obj, o.object_type otype, o.object_type otype, ash.p1 ash.p1 from v$active_session_history ash from v$active_session_history ash,all_objects o,all_objects o where ( event like 'db file s%' or event like 'direct%' ) where ( event like 'db file s%' or event like 'direct%' ) and o.object_id (+)= ash.CURRENT_OBJ# and o.object_id (+)= ash.CURRENT_OBJ# and sample_time > sysdate - &v_minutes/(60*24) and sample_time > sysdate - &v_minutes/(60*24) group by group by CURRENT_OBJ#, CURRENT_OBJ#, o.object_name, o.object_name, o.object_type, o.object_type, ash.p1, ash.p1, sql_id sql_id ) io, dba_data_files f dba_data_files fwhere f.file_id = io.p1 f.file_id = io.p1 Order by tcnt, io.sql_id, io.cnt TCNT SQL_ID CNT AAS OBJN OBJ P1 TABLESPAC yas01u2p9ch ITEM_PRODUCT_IX 7 SOEINDEX ORDER_ITEMS_UK 7 SOEINDEX ITEM_ORDER_IX 7 SOEINDEX 58 6v6gm0fd1rgrz WAIT_OBJECTS 1 SYSTEM UNDOTBS1

#.21 Copyright 2006 Kyle Hailey Missing Object IDs  dba_extents – get object name  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 select segment_name, segment_type from dba_extents where file_id = P1 and P2 between block_id and block_id + blocks – 1; select segment_name, segment_type from dba_extents where file_id = P1 and P2 between block_id and block_id + blocks – 1;

#.22 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 SYS SMON_SCN_TO_TIME CLUSTER 11 SYS SMON_SCN_TO_TIME CLUSTER 993 SYS _SYSSMU7$ TYPE2 UNDO 993 SYS _SYSSMU7$ TYPE2 UNDO 150 rows selected. Elapsed: 00:00:01.03

#.23 Copyright 2006 Kyle Hailey IO Solutions 1.Check average read times per file  Should be between 5-20 ms  Data in Statspack under “File IO Stats” 2.Check Cache buffer Hit ratio  Check db_cache_advice 9i and higher  Data in Statspack under “Buffer Pool Advisory”  Want to optimize data caching 3.Tune High IO SQL

#.24 Copyright 2006 Kyle Hailey Step 1a: Ave Read Time File IO Stats DB/Inst:labsf03 Snaps: 1-2 Tablespace Filename Av Mx Av Av Rd Rd Av Av Buffer BufWt Reads Reads/s (ms) Bkt Blks/Rd Writes Writes/s Waits (ms) SYSTEM /u01/app/oracle/oradata/labsf03/system01.dbf , , USERS /u01/app/oracle/oradata/labsf03/users01.dbf ### 1.0 9, File IO Stats DB/Inst:labsf03 Snaps: 1-2 Tablespace Filename Av Mx Av Av Rd Rd Av Av Buffer BufWt Reads Reads/s (ms) Bkt Blks/Rd Writes Writes/s Waits (ms) SYSTEM /u01/app/oracle/oradata/labsf03/system01.dbf , , USERS /u01/app/oracle/oradata/labsf03/users01.dbf ### 1.0 9, IO should be under 20ms Fastest possible is around 7ms Faster speeds are due to read caching

#.25 Copyright 2006 Kyle Hailey Step 1c: Ave Read Time IO should be under 20ms Fastest possible is around 7ms Faster speeds are due to read caching select to_char(begin_interval_time,'yyyy-mm-dd hh24:mi') snap_time, file#, readtim/nullif(phyrds,0) avg_read_ms, phyrds from DBA_HIST_FILESTATXS f, dba_hist_snapshot s where f.snap_id=s.snap_id ; select to_char(begin_interval_time,'yyyy-mm-dd hh24:mi') snap_time, file#, readtim/nullif(phyrds,0) avg_read_ms, phyrds from DBA_HIST_FILESTATXS f, dba_hist_snapshot s where f.snap_id=s.snap_id ; SNAP_TIME FILE# AVG_READ_MS PHYRDS : : : : : : : : : : : : SNAP_TIME FILE# AVG_READ_MS PHYRDS : : : : : : : : : : : :

#.26 Copyright 2006 Kyle Hailey Step 1c: Ave Read Time IO should be under 20ms Fastest possible is around 7ms Faster speeds are due to read caching select to_char(begin_time,'yyyy-mm-dd hh24:mi') begin_time, file_id fid, average_read_time *10 avgrd_ms, average_write_time *10 avgwr_ms, physical_reads pr, physical_writes pw from V$FILEMETRIC_HISTORY f order by begin_time; select to_char(begin_time,'yyyy-mm-dd hh24:mi') begin_time, file_id fid, average_read_time *10 avgrd_ms, average_write_time *10 avgwr_ms, physical_reads pr, physical_writes pw from V$FILEMETRIC_HISTORY f order by begin_time; BEGIN_TIME FID AVGRD_MS AVGWR_MS PR PW : : : : : BEGIN_TIME FID AVGRD_MS AVGWR_MS PR PW : : : : :

#.27 Copyright 2006 Kyle Hailey Step 2 : Buffer Pool Advisory Buffer Pool Advisory Size for Size Buffers for Read Estimated P Est (M) Factor Estimate Factor Physical Reads D , ,928 D , ,043 D , ,772 D , ,715 D , ,715 D , ,715 D , ,715 D , ,715 D , ,715 D 1, , ,715 Buffer Pool Advisory Size for Size Buffers for Read Estimated P Est (M) Factor Estimate Factor Physical Reads D , ,928 D , ,043 D , ,772 D , ,715 D , ,715 D , ,715 D , ,715 D , ,715 D , ,715 D 1, , ,715

#.28 Copyright 2006 Kyle Hailey Step 3: Find Top I/O SQL select count(*),sql_id, event from v$active_session_history where event in ('db file sequential read', 'db file scattered read', 'db file parallel read') group by sql_id, event order by count(*); select count(*),sql_id, event from v$active_session_history where event in ('db file sequential read', 'db file scattered read', 'db file parallel read') group by sql_id, event order by count(*); COUNT(*) SQL_ID EVENT hk7xvhua40va db file sequential read 335 3hatpjzrqvfn7 db file sequential read 343 0uuqgjq7k12nf db file sequential read 481 db file scattered read g9y3xmvd db file sequential read 1158 db file sequential read bzhqhhj9mpaa db file sequential read zu158rqf4kf db file sequential read yas01u2p9ch4 db file sequential read COUNT(*) SQL_ID EVENT hk7xvhua40va db file sequential read 335 3hatpjzrqvfn7 db file sequential read 343 0uuqgjq7k12nf db file sequential read 481 db file scattered read g9y3xmvd db file sequential read 1158 db file sequential read bzhqhhj9mpaa db file sequential read zu158rqf4kf db file sequential read yas01u2p9ch4 db file sequential read

#.29 Copyright 2006 Kyle Hailey Step 3: OEM find top SQL

#.30 Copyright 2006 Kyle Hailey IO Solutions  Check  File IO response times  Buffer Cache Hit Ratio  Always Check SQL to Tune

#.31 Copyright 2006 Kyle Hailey IO Configuration Issues  Unix Buffer Cache  Disk Spindles  Raid 5

#.32 Copyright 2006 Kyle Hailey Machine Memory Unix File Buffer CacheSGA Unix File Cache If average IO read times are under 7ms them probably coming from Unix File Cache

#.33 Copyright 2006 Kyle Hailey IO Histograms IO at > 1ms comes From Unix File Cache

#.34 Copyright 2006 Kyle Hailey IO Throughput  IO Operations/Sec  150 IOPS/sec optimistic Large Disks – Few IOPS Small Disks – Many IOPS

#.35 Copyright 2006 Kyle Hailey Disk 2Gb vs 70GB Seagate Barracuda 4LP Seagate Cheetah 73LP Capacity2.16GB73.4GB Rotation Speed7200rpm10000rpm Rotational Delay(avg)4.1ms3ms Time to read 32Kb6ms3ms Seek Time (avg)9.4ms4.9 Total time for Single I/O19.5ms10.9ms I/O per second (conservative) 5192 IOPs/sec per 100GB

#.36 Copyright 2006 Kyle Hailey Raid 5 B – Battle A – Against A – Any R – Raid F - Five

#.37 Copyright 2006 Kyle Hailey 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

#.38 Copyright 2006 Kyle Hailey Direct IO ShadowProcess Buffer Cache PGA Sort Area Direct Path PQO Reads X

#.39 Copyright 2006 Kyle Hailey direct path read  Parallel Query  See v$px_session _serial_direct_read = true select parameter1, parameter2, parameter3 from v$event_name where name='direct path read'; PARAMETER1 PARAMETER2 PARAMETER file number first dba block cnt

#.40 Copyright 2006 Kyle Hailey Further Investigation ASH SID QSID P3 OBJN OTYPE FN BLOCKN SQL_ID TOTO TABLE gp8tg0b2s TOTO TABLE gp8tg0b2s TOTO TABLE gp8tg0b2s TOTO TABLE gp8tg0b2s TOTO TABLE gp8tg0b2s TOTO TABLE gp8tg0b2s TOTO TABLE gp8tg0b2s SID QSID P3 OBJN OTYPE FN BLOCKN SQL_ID TOTO TABLE gp8tg0b2s TOTO TABLE gp8tg0b2s TOTO TABLE gp8tg0b2s TOTO TABLE gp8tg0b2s TOTO TABLE gp8tg0b2s TOTO TABLE gp8tg0b2s TOTO TABLE gp8tg0b2s722 select session_id sid, QC_SESSION_ID qsid, ash.p3, CURRENT_OBJ#||' '||o.object_name objn, o.object_type otype, CURRENT_FILE# fn, CURRENT_BLOCK# blockn, ash.SQL_ID from v$active_session_history ash, all_objects o where event like 'direct path read' and o.object_id (+)= ash.CURRENT_OBJ# Order by sample_time; select session_id sid, QC_SESSION_ID qsid, ash.p3, CURRENT_OBJ#||' '||o.object_name objn, o.object_type otype, CURRENT_FILE# fn, CURRENT_BLOCK# blockn, ash.SQL_ID from v$active_session_history ash, all_objects o where event like 'direct path read' and o.object_id (+)= ash.CURRENT_OBJ# Order by sample_time;

#.41 select ash.SQL_ID, QC_SESSION_ID qsid, count(*) cnt, count (distinct session_id) deg, nvl(o.object_name,to_char(CURRENT_OBJ#)) obj, o.object_type otype, decode(session_state, 'WAITING',event,'CPU') event from v$active_session_history ash, all_objects o where o.object_id (+)= ash.CURRENT_OBJ# and qc_session_id is not null group by qc_session_id, sql_id, o.object_name, o.object_type, CURRENT_OBJ#, event, session_state Order by qc_session_id, sql_id PQO - ASH SQL_ID QSID CNT DEG OBJ OTYPE EVENT rvy3wj2u0h6u WAIT_OBJECTS TABLE direct path read WAIT_OBJECTS TABLE CPU WAIT_OBJECTS TABLE CPU db file sequential read db file sequential read read by other session read by other session CPU CPU 7p3jt75phub2d WAIT_OBJECTS TABLE PX Deq Credit: send blkd WAIT_OBJECTS TABLE PX qref latch WAIT_OBJECTS TABLE PX qref latch WAIT_OBJECTS TABLE db file sequential read WAIT_OBJECTS TABLE db file sequential read WAIT_OBJECTS TABLE direct path read WAIT_OBJECTS TABLE direct path read WAIT_OBJECTS TABLE CPU WAIT_OBJECTS TABLE CPU PX Deq Credit: send blkd PX Deq Credit: send blkd db file sequential read db file sequential read

#.42 Copyright 2006 Kyle Hailey direct path write   Occurs when:   insert /*+ APPEND */   sql*loader direct=y   Create table as select select parameter1, parameter2, parameter3 from v$event_name where name='direct path write'; PARAMETER1 PARAMETER2 PARAMETER file number first dba block cnt

#.43 Copyright 2006 Kyle Hailey Direct Path Read Temp Direct Path Write Temp  Sorting  Write to Temp  Read from Temp select parameter1, parameter2, parameter3 from v$event_name where name in ('direct path write temp‘, ‘direct path read temp’); ‘direct path read temp’); PARAMETER1 PARAMETER2 PARAMETER file number first dba block cnt

#.44 Copyright 2006 Kyle Hailey Further investigation “real time“ can use Select su.username, su.segtype, s.sql_id, su.blocks from v$sort_usage su, v$session s Where s.saddr = su.session_addr and s.serial# = su.session_num; Select su.username, su.segtype, s.sql_id, su.blocks from v$sort_usage su, v$session s Where s.saddr = su.session_addr and s.serial# = su.session_num; USERNAME SEGTYPE SQL_ID BLOCKS SYS SORT 3xp88dstadjs Note: SQL_ID doesn’t seem filled in for v$sort_usage.sql_id

#.45 Copyright 2006 Kyle Hailey sort segment request  SMON allocates sort space in Temp Tablespace  If SMON is busy this can cause waits for sort space  SMON may be stuck rolling back

#.46 Copyright 2006 Kyle Hailey file open  Args  P1 fib  P2 iov  P3 0  Wait on an open file  The time it takes to open the file  Times should be order of a block read  To tune, try pre-opening files  Leave sessoins connected  High reconnection rates can exacerbate  Can try holding log files open  (see script from Steve Adams)

#.47 Copyright 2006 Kyle Hailey file identify  The time it takes to identify a file so that it can be opened later.  Datafile should be identified just once  Logfiles are identified every checkpoint  Reduce checkpoints  Arguments  p1 fib  p2 filename  p3 opcode (1 test for create, 2 get details)

#.48 Copyright 2006 Kyle Hailey Data file init write  When autoextend is set and many extensions are happening

#.49 Copyright 2006 Kyle Hailey 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 fast_start_mttr_target

#.50 Copyright 2006 Kyle Hailey Further Investigation NAME P1 P2 P local write wait file# block# NAME P1 P2 P local write wait file# block# select * from v$event_name where name = ‘local write wait' select ash.p1,ash.p2, ash.SQL_ID, count(*) from v$ash ash where event='local write wait' group by ash.p1,ash.p2, ash.SQL_ID; P1 P2 SQL_ID COUNT q8k9xfmz0k2k q8k9xfmz0k2k q8k9xfmz0k2k q8k9xfmz0k2k 10

#.51 Copyright 2006 Kyle Hailey Temporary File #’s SQL> select file# from v$datafile; FILE# SQL> select file# from v$tempfile; FILE# SQL> show parameters db_files NAME VALUE db_files 200 Wait Temporary File#’s = Db_files + file# File# 201 = v$tempfile 1

#.52 Copyright 2006 Kyle Hailey Local Write Wait:extent allocation CREATE TEMPORARY TABLESPACE "NEWTEMP" TEMPFILE '/d3/temp01.dbf' SIZE 100M AUTOEXTEND ON EXTENT MANAGEMENT LOCAL UNIFORM SIZE 64K; select a.*, b.* from dba_objects a, dba_objects b order by a.owner ALTER DATABASE DEFAULT TEMPORARY TABLESPACE newtemp;

#.53 Copyright 2006 Kyle Hailey Local Write Waits

#.54 Copyright 2006 Kyle Hailey Local Write Wait: Solutions  Truncating a table  Reduce cache size  Use GTT  Temporary Table Space Allocations  Increase extent size

#.55 Copyright 2006 Kyle Hailey Summary I/O  Buffer Cache IO  db file sequential read  db file scattered read  db file parallel read  Tune  I/O’s should be 5-15ms  Check Buffer Cache Advisory  Tune SQL

#.56 Copyright 2006 Kyle Hailey Summary Direct I/O  direct path read : PQO  direct path write : direct path operations  direct path read temp: sorts  direct path write temp: sorts  direct path write (lob) : stored NOCACHE

#.57 Copyright 2006 Kyle Hailey IO Summary Other  sort segment request : SMON occupied  file open : log files or session reconnects  file identify : log files or session reconnects  local write wait –  Temp extensions  Truncates  data file init write – data file extension