Shared Pool Waits

#.2 Copyright 2006 Kyle Hailey Shared Pool Waits  Library Cache Latch  Shared Pool Latch  Library Cache Pin  Library Cache Lock  Library Cache Load Lock  Row Cache Lock

#.3 Copyright 2006 Kyle Hailey Hash Table handle Shared Pool Structure

#.4 Copyright 2006 Kyle Hailey Shared Pool Latch  Protects Space Allocation in the Shared Pool  Make sure two users don’t get same chunk of memory

#.5 Copyright 2006 Kyle Hailey Bucket sizes 0 < 80 bytes 1 < < < < < < < < < bigger Shared Pool Latch Shared Pool pre Memory Chunk Buckets

#.6 Copyright 2006 Kyle Hailey Shared Pool Free Space Shared Pool Latch covers changes in the lists of free memory chunks Shared Pool Latch

#.7 Copyright 2006 Kyle Hailey Get library cache latch Get shared pool latch Search right bucket Find best fit => If lists get long, search gets long Shared Pool Latch

#.8 Copyright 2006 Kyle Hailey Shared Pool Free Space Shared Pool Latch

#.9 Copyright 2006 Kyle Hailey Shared Pool Memory Chunk Buckets and up 0 16 bytes 1 20 bytes … ( only have one chunk size in bucket ) bytes to 872 …. ( only have 16 possible chunk sizes per bucket ) bigger Shared Pool Latch

#.10 Copyright 2006 Kyle Hailey library cache pin and locks  Locks control access, protects handle  Pins guarentees coherency, protects heaps  To Access to a cursor  Lock handle  Locking is the way of locating  Pin  Pinning loads any necessary heaps  Guarenteed to stay in memory until pin is released handle pin lock Heap 1 Child cursor 1 Heap 6 Heap 0

#.11 Copyright 2006 Kyle Hailey library cache lock and pins   Contention when Sessions try to load/compile same SQL at same time   Locks and Pins are usually in share mode unless modifications are being made

#.12 Copyright 2006 Kyle Hailey library cache lock handle pin lock   #20   P1 = address of object   P2 = address of lock   P3 = mode | namespace   See x$kgllk

#.13 Copyright 2006 Kyle Hailey library cache pin  #13  P1 = address of object  P2 = address of lock  P3 = Mode | Namespace  See x$kglpn handle pin lock

#.14 Copyright 2006 Kyle Hailey Solutions  Have only one Session compile a the same cursor at a time  Waits – find “competing” Sessions

#.15 Copyright 2006 Kyle Hailey SQL: Lib Cache Lock Find the waiters and who blocks them column wevent format a20 column bevent format a20 select waiter.sid waiter, waiter.p1raw wlockp1, waiter.event wevent, blocker_event.sid blocker, blocker_event.event bevent from x$kglpn p, gv$session blocker_session, gv$session_wait waiter, gv$session_wait blocker_event where p.kglpnuse=blocker_session.saddr and p.kglpnhdl=waiter.p1raw and (waiter.event like 'library cache lock' ) and blocker_event.sid=blocker_session.sid order by waiter.p1raw,waiter.sid /

#.16 Copyright 2006 Kyle Hailey library cache load lock  #23  Waiting For a Reload by another Session

#.17 Copyright 2006 Kyle Hailey Library Cache Latch  Protects changes in Library Cache  Library Locks are not atomic  Thus need library cache latch  Broken out into  library cache pin allocation  library cache lock allocation  library cache lock  library cache  library cache pin  library cache load lock

#.18 Copyright 2006 Kyle Hailey Hash Table handle pin lock Library Cache handle Find and Lock Pin (and Load)

#.19 Copyright 2006 Kyle Hailey Child cursor 3 Hash Table handle Cursor (0) pin lock Heap 1 Child cursor 1 Child cursor 2 Heap 6 pin lock Heap 0 pin lock waiters holders Handle Cursor(0) flags Library Cache Structures Library Cache Latch

#.20 Copyright 2006 Kyle Hailey Library Cache Latch Contention  Excesive Hard Parsing  Not Sharing SQL – use of Literal Values  Shared Pool too small  Too many invalidations  Excessive Soft Parsing

#.21 Copyright 2006 Kyle Hailey Sharing SQL & Literals PLAN_HASH_VALUE CNT SQL_TEXT SELECT * FROM dual WHERE dummy= SELECT * FROM dual WHERE dummy= SELECT * FROM dual WHERE dummy= SELECT * FROM dual WHERE dummy= SELECT * FROM dual WHERE dummy= SELECT * FROM dual WHERE dummy= SELECT * FROM dual WHERE dummy= SELECT * FROM dual WHERE dummy= SELECT * FROM dual WHERE dummy= select plan_hash_value, plan_hash_value,count(plan_hash_value)fromv$sql group by plan_hash_value, order by count(plan_hash_value) select plan_hash_value, plan_hash_value,count(plan_hash_value)fromv$sql group by plan_hash_value, order by count(plan_hash_value) select sql_text from v$sql where plan_hash_value = and rownum < 10; select sql_text from v$sql where plan_hash_value = and rownum < 10;

#.22 Copyright 2006 Kyle Hailey Cursor Sharing  Bind Variables  Select * from dual where dummy = :var;  Cursor_Sharing  Cursor_sharing = Force Oracle replaces variables with bind variables  Defaults to Exact

#.23 Copyright 2006 Kyle Hailey Shared Pool too Small  Reloads means Cursor heaps were kicked out implying shared_pool too small SQL> select namespace, reloads from v$librarycache; from v$librarycache; NAMESPACE RELOADS SQL AREA 367 TABLE/PROCEDURE 592 SQL> select namespace, reloads from v$librarycache; from v$librarycache; NAMESPACE RELOADS SQL AREA 367 TABLE/PROCEDURE 592

#.24 Copyright 2006 Kyle Hailey Invalidations  Changes in dependent objects invalidate cursor FOR i IN LOOP l_cursor:=dbms_sql.open_cursor; dbms_sql.parse(l_cursor, 'SELECT * FROM toto',dbms_sql.native); execute immediate 'analyze table toto compute statistics'; dbms_sql.close_cursor(l_cursor); END LOOP; SQL> select namespace, invalidations invalidations from v$librarycache; from v$librarycache; NAMESPACE INVALIDATIONS SQL AREA 6065 SQL> select namespace, invalidations invalidations from v$librarycache; from v$librarycache; NAMESPACE INVALIDATIONS SQL AREA 6065

#.25 Copyright 2006 Kyle Hailey Re-Executing a Cursor 1.Libray Cache latch 2.Locks 3.Pins pin lock Execute 1Execute 2Execute 3Execute 4Execute 5 Cursor Memory lock = Latch Soft Parsing

#.26 Copyright 2006 Kyle Hailey Session Cached Cursors Execute 1Execute 2Execute 3Execute 4Execute 5 Cursor Memory lock = Latch pin Session_cached_cursor: If Opening/Closing keeps locked in Memory

#.27 Copyright 2006 Kyle Hailey Session Cached Cursors FOR i IN LOOP FOR i IN LOOP l_cursor:=dbms_sql.open_cursor; l_cursor:=dbms_sql.open_cursor; dbms_sql.parse(l_cursor,'SELECT * FROM dual’,dbms_sql.native); dbms_sql.parse(l_cursor,'SELECT * FROM dual’,dbms_sql.native); dbms_sql.close_cursor(l_cursor); dbms_sql.close_cursor(l_cursor); END LOOP; END LOOP; FOR i IN LOOP FOR i IN LOOP l_cursor:=dbms_sql.open_cursor; l_cursor:=dbms_sql.open_cursor; dbms_sql.parse(l_cursor,'SELECT * FROM dual’,dbms_sql.native); dbms_sql.parse(l_cursor,'SELECT * FROM dual’,dbms_sql.native); dbms_sql.close_cursor(l_cursor); dbms_sql.close_cursor(l_cursor); END LOOP; END LOOP; Session_cached_cursors=0 Latch Gets library cache lock 120,028 library cache 180,074 library cache pin 60,048 Session_cached_cursors=20 library cache lock 4 library cache 60,061 library cache pin 60,048

#.28 Copyright 2006 Kyle Hailey Cursor Space for Time Execute 1Execute 2Execute 3Execute 4Execute 5 Cursor Memory Cursor_space_for_time=true : if open and re-executing – keeps cursor pinned (Cursor already locked because cursor is kept open) = Latch pin lock OpenCursor CloseCursor

#.29 Copyright 2006 Kyle Hailey Cursor Space For Time FOR i IN LOOP rc:=dbms_sql.execute(l_cursor); rc:=dbms_sql.execute(l_cursor); IF DBMS_SQL.FETCH_ROWS (l_cursor) < 0 THEN IF DBMS_SQL.FETCH_ROWS (l_cursor) < 0 THEN DBMS_SQL.COLUMN_VALUE (l_cursor, 1, cnt); DBMS_SQL.COLUMN_VALUE (l_cursor, 1, cnt); end if; end if; FOR i IN LOOP rc:=dbms_sql.execute(l_cursor); rc:=dbms_sql.execute(l_cursor); IF DBMS_SQL.FETCH_ROWS (l_cursor) < 0 THEN IF DBMS_SQL.FETCH_ROWS (l_cursor) < 0 THEN DBMS_SQL.COLUMN_VALUE (l_cursor, 1, cnt); DBMS_SQL.COLUMN_VALUE (l_cursor, 1, cnt); end if; end if; Cursor_space_for_time=false Latch Gets library cache lock 35 library cache 60,096 library cache pin 60,044 Cursor_space_for_time=true library cache lock 30 library cache 85 library cache pin 42

#.30 Copyright 2006 Kyle Hailey Efficient Lock and Pinning  Reduce use of latches  Improve throughput  Improve Concurrency ***

#.31 Copyright 2006 Kyle Hailey row cache lock : args  P1 = cache#  P2 = Lock Mode Held  P3 = Lock Mode Requested select parameter as “name” from v$rowcache where cache# = P1; select parameter as “name” from v$rowcache where cache# = P1;

#.32 Copyright 2006 Kyle Hailey Summary  Shared Pool Latch  Shard pool too small or too much hard pasing  Loading Same Cursor  Library Cache Pin  Library Cache Lock  Library Cache Load Lock  Library Cache Latch  Too much hard or soft parsing  Row Cache Lock

#.33 Copyright 2006 Kyle Hailey Library Cache Latch Solutions  Share Cursors  Use bind variables  User cursor_sharing=force  Avoid invalidations and reloads  Size shared_pool large enough  Avoid changing dependent objects  Soft Parsing  Session_cached_cursors =20 : keep across open/close  Cursor_space_for_time=true : keep pinned across executes  hold_cursor=true : used in precompilers