Oracle 10g Performance: chapter 09 enqueues

Enqueue Waits : Locks

Kyle Hailey
http://perfvision.com/ftp/emea2010
kylelf@gmail.com

#.1

Locks Covered in this Section
Part I : Intro
 Lock Name(type) and Mode
 Finding waiter and blocker
 Finding Object
Part II : User
 TM – table modification
 TX – Transaction locks
 UL – user lock
Part III : Internal
 CI – Cross Instance
 HW – High Water
 RO – Reusable Object
Copyright 2006 Kyle Hailey #.2

Part I : Intro
To Solve we need:

1.Waiter
2.Blocker
3.Lock Type
 type
 mode
1.Object blocking on

Missing : blocking SQL
 Possibly with log miner


Solving – Data Sources
 V$active_session_history

or

 In “real time” can also use
 v$lock
 v$session (v$session_wait)
 dba_blockers
 dba_waiters
 ?/rdbms/admin/utllockt.sql
 http://www.evdbt.com/enqwaits.sql


v$active_session_history
Fields in ASH for lock analysis and solution:
 Waiter SQL Waiting
 SESSION_ID
SQL_ID
 SESSION_SERIAL#
Blocker
 USER_ID
 BLOCKING_SESSION
 Object
 BLOCKING_SESSION_STATUS
 CURRENT_OBJ#
 CURRENT_FILE#  BLOCKING_SESSION_SERIAL#

 CURRENT_BLOCK# Lock Type and Mode
Event = Type (name)
P1 = Type | Mode

Missing: SQL Blocking not reliably
possible, Maybe by dumping REDO

Lock Name and Mode
Select parameter1 from v$event_name where name=‘enqueue’;

Parameter1
----------
Name|mode
Select p1, p1raw from v$session where event like 'enq%';

P1 P1RAW
---------- --------
1415053318 54580006

Name: 5458 Mode: 0006
Hex Decimal ASCII
54 = 84 = “T” Lock = TX 6
58 = 88 = “X”

Type and Mode

SELECT
SELECT
chr(bitand(p1,-16777216)/16777215)||
chr(bitand(p1,-16777216)/16777215)||
chr(bitand(p1, 16711680)/65535) Type,
chr(bitand(p1, 16711680)/65535) Type,
mod(p1,16) lmode
mod(p1,16) lmode
from v$session_wait
from v$session_wait
where event=‘enqueue’;
where event=‘enqueue’;
TY
TY LMODE
LMODE
-- ----------
-- ----------
TX
TX 6
6

#.7

Lock Names (types)
 9i
 One Wait : “enqueue”
 10g
 208enqueue waits
 Specific to each type of enqueue

enq: HW - contention Configuration
enq: SQ - contention Configuration
enq: SS - contention Configuration
enq: ST - contention Configuration
enq: TM - contention Application
enq: TW - contention Administrative
enq: TX - allocate ITL entry Configuration
enq: TX - index contention Concurrency
enq: TX - row lock contention Application
enq: TX – contention Application

Lock Modes

# Type Name
--- ------- ---------------------------
1 Null Null
2 SS Sub share
3 SX Sub exclusive
4 S Share
5 SSX Share/sub exclusive
6 X Exclusive


P1 = name | mode
 P1 (parameter1) same for all locks
select distinct parameter1 from v$event_name PARAMETER1
where name like 'enq:%' name|mode

select
event,
mod(p1,16) as "mode"
from v$active_session_history
where event like 'enq:%‘;

EVENT mode
enq: TX - allocate ITL entry 4
enq: TX - row lock contention 6
enq: TX - row lock contention 4


OEM 10g

if P1 = 1415053318
then mode = 6
Then it is a data block
row lock

Querying ASH
select
substr(event,0,20) lock_name,
ash.session_id waiter,
mod(ash.p1,16) lmode,
ash.p2 p2,
ash.p3 p3,
o.object_name object,
o.object_type otype,
CURRENT_FILE# filen,
CURRENT_BLOCK# blockn,
ash.SQL_ID waiting_sql,
BLOCKING_SESSION blocker
--,ash.xid
from
v$active_session_history ash,
all_objects o
where
event like 'enq: %'
and o.object_id (+)= ash.CURRENT_OBJ#
/


Part II : User Locks

 TX – Transaction Lock
 Mode 6: Modifying same row
 Mode 4: several reasons

 TM – Table Modification
 Mode 4: Unindexed Foreign Key
 UL – User Lock


TX Lock
Session B
Undo
Wait for Tx Segment
update toto set
update toto set To commit Header
name = ‘ADAMS’
name = ‘ADAMS’
where id = 1;
where id = 1; Undo
Segment
Table Toto
Data Block
Data Block
Header
Header
Transaction 1
Session a
update toto set
update toto set
name = ‘SMITH’
name = ‘SMITH’
Row 1 where id = 1;
Delete from 1;
where id = toto where id
Delete from toto where id
Copyright 2006 Kyle Hailey = 2;
= 2;
Delete from toto where id
Delete from toto where #.14
id

Transaction Locks (TX)
TX = Transaction = Wait on UNDO
 Mode 6 (exclusive)
 modification of a row lock
 Mode 4 (share)
 Index block spilt
 Unique Index Key enforcement
 Foreign key enforcement
 ITL space waits
 Bitmap chunk conflicts
 Alter tablespace … read only;
 Free Lists slot waits
 Possible with two phase commit


Transaction Locks (TX)

Mode 4, new Events:

1. enq: TX - allocate ITL entry
 Wait on an ITL slot
1. enq: TX - index contention
 Index block split
1. enq: TX - row lock contention
1. Mode 6 – classic row lock
2. Mode 4 - pk violation, fk violation, bitmap chunk wait
2. enq: TX – contention
 Wait for a data file extension, Alter tbs read only


enq: TX - row lock contention
Mode 6, row in data block
User 1 User 2
SQL> delete from toto
where id = 1;
SQL> delete from toto
where id =1;

Table
ID Value
1 foo



if P1 = 1415053318
then mode = 6
Then it is a data block
row lock


TX – Mode 4

if P1 = 1415053316
then mode = 4
Not same data but conflicts


Mode 4, happens for 3 reasons
1. Unique key contention
2. Foreign Key contention
3. Bitmap index contention
(others?)


Mode 4 , unique index
User 1 User 2
create table p(n number);
create unique index p_i on p(n);
insert into p values(2);
insert into p values(2);

PK Table

ID ID Value
2? 2?


Mode 4, foreign key
User 1 User 2
create table parent (
id number primary key);
create table child (
id number references parent,
name varchar2(20));
insert into parent values (2);
insert into child values (2,88);
PK Parent Child
ID ID Value ID Name
2? 2? 2



 Mode 4
 Bitmaps are compressed
 Changes to the same bitmap cause locks
Value Start End Bitmap
Rowid Rowid
1 01010000111000011100001100
000.000.0000 000.000.000

2 01010000111000011100001100
000.000.0000 000.000.000


Session 1
create table t1 ((
create table t1 Different rows but
n1
n1 number(4),
number(4), same key value
n2
n2 number(4));
number(4));
insert into t1
insert into t1
select 1, rownum
select 1, rownum
from all_objects
from all_objects
where rownum <= 400;
where rownum <= 400;
commit;
commit;
create bitmap index i1 on t1(n1);
create bitmap index i1 on t1(n1);
update t1 set n1 = 2
where n2 = 12;
where n2 = 12; Session 2
where n2 = 13;
where n2 = 13;

 Bitmaps are compressed
 Changes to the same bitmap chunk cause
locks
Rowid Rowid
1 01010000111000011100001100
200.0 204.7
1 01010000111000011100001100
205.0 210.3
2 01010000111000011100001100
200.0 205.6

block row


Rowid Rowid
1 01010000111000011100001100
200.0 204.7
2 01010000111000011100001100
205.0 210.3
3 01010000111000011100001100
200.0 205.6

Session 1 Session 2
Update id=12 Update id=13
set value 2 set value 2

Summary: TX 4 from ASH
uniq index
ST EVENT SID LM P2 P3 OBJ OTYPE FN BLOCKN SQL_ID BSID
----- ---------------------- --- --- ------ ---- ----- ----- --- ------ --
10:39 enq: TX - row lock c 141 4 655406 6672 -1 0 0 bjvx94vnxtxgv 158

FK (10.2.0.3)
----- ---------------------- --- --- ------ ---- ----- ----- --- ------ --
10:41 enq: TX - row lock c 144 4 179681 7074 CHILD TABLE 1 60954 ahm7c9rupbz9r 1

bitmap
----- ---------------------- --- --- ------ ---- ----- ----- --- ------ --
10:41 enq: TX - row lock c 143 4 966081 4598 I1 INDEX 0 0 azav296xxqcjx 144


enq: TX - allocate ITL entry

Transaction 1 Info
Data Block
Data Block Transaction 2 Info
Header
Header
ITL

Data



Data Block
Data Block
Header
Header
Transaction 1 Transaction 3
Transaction 2
Row 3
Row 2
Data
Row 1


create table itl (
create table itl (
id number,
id number,
data varchar2(20)
data varchar2(20)
))
pctfree 0
pctfree 0
initrans 1
initrans 1
;;
insert into itl select rownum,'a' from all_objects
insert into itl select rownum,'a' from all_objects
where rownum < 2000;
where rownum < 2000;
commit;
commit;
session 1: update itl set data=data where id=1;

enq: TX - contention

1. Altering tablespace read only with open transaction
Example
 Session 1 – start transaction, don’t commit
 Session 2 – alter tablespace read only

1. Data File Extension – waiter waiting for another session to extend
file
2. Index Block Split – waiter waiting for another session to split the
block


TX Further Investigation

select event, sql_id,
CURRENT_OBJ# || ' ' || name obj
,CURRENT_FILE# file#
,CURRENT_BLOCK# block#
from v$active_session_history ash,
obj$ o
where
event like 'enq: TX%'
and o.obj# (+)= ash.current_obj#
order by sample_time

EVENT SQL_ID OBJ FILE# BLOCK#
enq: TX - row lock contention ahm7c9rupbz9r 53363 FOO 1 123586
enq: TX - row lock contention bjvx94vnxtxgv 53363 FOO 1 123586
enq: TX - row lock contention bjvx94vnxtxgv 53363 FOO 1 123586

TX Further Investigation

Who is the blocker:

V$active_session_history :
BLOCKING_SESSION
BLOCKING_SESSION_STATUS
BLOCKING_SESSION_SERIAL#

No Guarentee of finding blocker SQL


enq: TM - contention

 TX locks have a corresponding TM lock
 TM locks the structure from change

 Parameter1 = object id
LOCK
LOCK Parmeter1
Parmeter1 Parmeter2(ID1) Parameter3(ID2)
Parmeter2(ID1) Parameter3(ID2)
------- ---------
------- --------- -------------
------------- ---------------
---------------
enq: TM name|mode
enq: TM name|mode object #
object # table/partition
table/partition



Exclusive Row Level Lock

User 1 User 2
create table parent (
id number primary key);
create table child (
id number references parent,
name varchar2(20));
commit;
insert into child values (1,2);
delete from parent where id=2;



PK Parent Child
ID ID Value ID Name
1 1 1
X
2 X
2

Session 1 Insert into Child ID=1

Session 2 Delete from Parent where ID=2 :
Enqueue TM 4
Session 2 doesn’t know the value Session 1 inserted
Session 2 only knows there is an outstanding change

enq: TM – contention Solution

PK Parent Child
Index
ID ID Value ID ID Name
1 1
2

Foreign Key

Session 1: Insert into Child ID=1
Session 2: Delete from Parent ID=2
OK – can verify quickly in the child index

TM Further Investigation
select
event,
sql_id,
mod(p1,16) as "mode",
p2|| ' ' || o.name obj
obj$ o
where
event like 'enq: TM%'
and o.obj# (+)= ash.p2
order by sample_time;
EVENT SQL_ID mode OBJ
enq: TM - contention 8zw36yw3fq4yy 4 53372 CHILD


UL Locks
 User-defined Locks
 dbms_lock

Wait Event Parameter2 Parameter3
enq: UL - contention id 0

dbms_lock.allocate_unique(v_lockname, v_lockhandle);
dbms_lock.request(v_lockhandle, p_ltype);
dbms_lock.release(v_lockhandle);


Internal Locks

 KO – fast object checkpoint
 RO – Reuse Object
 SQ – Sequence Lock
 ST – Space Transaction


enq: CI - contention
 Cross Instance
 not OPS lock.
 invoke actions in background processes
 checkpoints
 log switches
 instance is shut down


CI – Cross Instance

Id1 Meaning (parameter2)
Id1 Meaning (parameter2) Id2 Meaning (parameter3)
Id2 Meaning (parameter3)
00Flush buffers for reuse as new class
Flush buffers for reuse as new class 11Pass in Parameters
Pass in Parameters
11LGWR checkpointing and Hot Backup
LGWR checkpointing and Hot Backup 22Invoke the call in background process
Invoke the call in background process
22DBWR synchronization of SGA with control file
DBWR synchronization of SGA with control file 33Foreground has not returned yet
Foreground has not returned yet
33Log file add/drop/rename notification 44Used to allocate the CI call
Used to allocate the CI call
Log file add/drop/rename notification
44Write buffer for CR read 55Used to queue up interested clients
Used to queue up interested clients
Write buffer for CR read
55Test Call
Test Call
66Invalidate KCK cache in all instances
Invalidate KCK cache in all instances
77Alter rollback segment optimal
Alter rollback segment optimal
88Signal Query Servers/coordinator
Signal Query Servers/coordinator
99Create Remote Parallel Query Server
Create Remote Parallel Query Server
10 Set Global Partitions
10 Set Global Partitions
11 Stop Disk Writes
11 Stop Disk Writes
12 Drop Sort Segments
12 Drop Sort Segments
13 Release unused space from Sort Segments
13 Release unused space from Sort Segments
14 Instance Recovery for Parallel operation Group
14 Instance Recovery for Parallel operation Group
15 Validate parallel slave Lock Value
15 Validate parallel slave Lock Value
16 Check Transaction State Objects
16 Check Transaction State Objects


CI Locks
select
substr(sql_text,0,20) sql_text,
p2,p3,
obj$ o,
v$sqltext sql
where
event like 'enq: CI%'
and sql.sql_id (+)= ash.sql_id

SQL_TEXT P2 P3 OBJ FILE# BLOCK#

INSERT INTO TOTO1 VA 1 5 54225 TOTO1 6 682721


CI Locks

SQL_TEXT
SQL_TEXT P2 P3
P2 P3
---------------------------------------- --- --
---------------------------------------- --- --
alter table XXXXX drop partition YYYYY
alter table XXXXX drop partition YYYYY 1 5
1 5
P2 = 1 ""LGWR checkpointing and Hot Backup ""
P2 = 1 LGWR checkpointing and Hot Backup

P3 = 5. "Used to queue up interested clients""
P3 = 5. "Used to queue up interested clients

If p2=1 and p3=5, then contention on blocks being
checkpointed, try raising fast_start_mttr_target

alter system set fast_start_mttr_target=600 scope=both;


enq: HW - contention

Wait Event Parameter2 Parameter3
enq: HW - contention table space # block

Session 1 Header
Table
Session 2
Data
Session 3

High Water Mark
Empty


HW

 Use Freelists
 Cause a jump in High Water Mark by freelists *
_bump_highwater_mark_count
 Hidden Parameter
 _bump_highwater_mark_count
 alter session set "_bump_highwater_mark_count"=100;
 Not supported
 ASSM
 Automatic segment space management


HW Further Investigation

select
event,
sql_id,
obj$ o
where
event like 'enq: HW%'

EVENT SQL_ID OBJ FILE# BLOCK#
enq: HW - contention 49ch3jfkncnsp 53410 T1_I1 13 29734


enq: KO - fast object checkpoint
 Used when checking the cache for blocks from a
table for PQO direct read


enq: RO - fast object reuse
 Drop or Truncate a table
 Wait for DBWR to clean cache
 Solution
 Tune DBWR using smaller MTTR
 Use GTT
 Truncate/drop less often

#.49

Other Resources

@?/rdbms/admin/utllockt
WAITING_SESSION LOCK_TYPE MODE_REQUESTED MODE_HELD LOCK_ID1 LOCK_ID2
--------------- ----------- -------------- --------- --------- --------
144 None
139 Transaction Share Exclusive 131113 7507


Blocking Sessions


Summary : Internal Locks
 Look at object and SQL
 use ASSM, freelists, pre-allocate extents
 KO – fast object checkpoint
 PQO
 RO – reusable object
 Reduce cache, tune DBWR, use GTT
 SQ – Sequence Lock
 logon/logoff problem
 ST - Space Transaction
 only one per database
 used for space allocations uet, fet
 Find object
 use LMT


Oracle 10g Performance: chapter 09 enqueues

Empfohlen

Empfohlen

Weitere ähnliche Inhalte

Was ist angesagt?

Was ist angesagt? (20)

Ähnlich wie Oracle 10g Performance: chapter 09 enqueues

Ähnlich wie Oracle 10g Performance: chapter 09 enqueues (20)

Mehr von Kyle Hailey

Mehr von Kyle Hailey (20)

Kürzlich hochgeladen

Kürzlich hochgeladen (20)

Oracle 10g Performance: chapter 09 enqueues

Hinweis der Redaktion