删除主表 子表外键没有索引的性能优化

整个表147M，执行时一个CPU耗尽， buffer gets 超过1个G， 启用并行也没有用

 

今天开发的同事问有个表上的数据为什么删不掉？我看了一下，也就不到100000条数据，表上有外键，等了5分钟hang在那里，时间原因，我对表上的外键禁用后，瞬间删除。

现在来还原这个问题。

sys@ANBOB>select count(*) from bjhr.doctor_exam_member;
COUNT(*)
——————–
92102

sys@ANBOB>delete bjhr.doctor_exam_member;
–hang

–等待10分钟都未执行完,检查表的外键信息

bjhr@ANBOB>SELECT /*+RULE*/D.CONSTRAINT_NAME pk_name,-- d.table_name,D.TABLE_NAME || '.' || D.COLUMN_NAME pk_column,A.CONSTRAINT_TYPE,B.CONSTRAINT_NAME fk_name,B.TABLE_NAME || '.' || B.COLUMN_NAME fk_columnFROM user_constraints aJOIN user_cons_columns bON a.constraint_name = b.constraint_name AND a.owner = b.ownerJOIN user_constraints cON A.R_CONSTRAINT_NAME = C.CONSTRAINT_NAME AND A.R_OWNER = c.ownerJOIN user_cons_columns dON c.constraint_name = d.constraint_name AND c.owner = d.ownerWHERE D.table_name = 'DOCTOR_EXAM_MEMBER'
bjhr@ANBOB>/PK_NAME              PK_COLUMN                                C FK_NAME                        FK_COLUMN
-------------------- ---------------------------------------- - ------------------------------ -------------------------------------------------------
PK_DOCTOR_EXAM_MEMBE DOCTOR_EXAM_MEMBER.DOCTOR_EXAM_MEMBER_ID R FK_RESULT_N_REFERENCE_DOCTOR   RESULT_NOTIFICATION_RECORD.DOCTOR_EXAM_MEMBER_ID
PK_DOCTOR_EXAM_MEMBE DOCTOR_EXAM_MEMBER.DOCTOR_EXAM_MEMBER_ID R RESULT_RE_DOCTOR_MEMBER        DOCTOR_EXAM_RESULT.DOCTOR_EXAM_MEMBER_ID

–有外键，之前已对子表进行过删除，否则会报错ORA-02266

delete RESULT_NOTIFICATION_RECORD;
delete DOCTOR_EXAM_RESULT;
commit;

–下面开始分析，创建新的session

sys@ANBOB>select xidsqn,xidusn,object_id,session_id,locked_mode from v$locked_object;XIDSQN               XIDUSN            OBJECT_ID           SESSION_ID          LOCKED_MODE
-------------------- -------------------- -------------------- -------------------- --------------------2102                  203              1639631                 2290                    32102                  203              1639572                 2290                    3sys@ANBOB>select object_name,object_type from dba_objects where object_id in(1639631,1639572);OBJECT_NAME                    OBJECT_TYPE
------------------------------ -------------------
DOCTOR_EXAM_MEMBER             TABLE
DOCTOR_EXAM_RESULT             TABLEsys@ANBOB>select event,p1,p2,p1text,p2text,seconds_in_wait,state from v$session_wait where sid=2290;
EVENT                                   P1    P2 P1TEXT               P2TEXT                    SECONDS_IN_WAIT STATE
------------------------------ ----------- ----- -------------------- -------------------- -------------------- -------------------
latch: shared pool              1611704464   307 address              number                                213 WAITED SHORT TIME--trace hanganalyze and systemstatealter session set events 'immediate trace name systemstate level 266';
alter session set events 'immediate trace name hanganalyze level 3';--hanganalyze trace 
===============================================================================Chains most likely to have caused the hang:[a] Chain 1 Signature: Chain 1 Signature Hash: 0x673a0128[b] Chain 2 Signature: 'Streams AQ: waiting for messages in the queue'Chain 2 Signature Hash: 0xa00e2e87===============================================================================
Sessions in an involuntary wait or not in a wait:-------------------------------------------------------------------------------
Chain 1:
-------------------------------------------------------------------------------Oracle session identified by:{instance: 1 (ANBOB.ANBOB)os id: 27158process id: 94, oracle@dev-db (TNS V1-V3)session id: 2290session serial #: 7981}is not in a wait:{last wait: 11 min 0 sec agoblocking: 0 sessionswait history:1.       event: 'latch: shared pool'time waited: 0.000114 secwait id: 183             p1: 'address'=0x6010a890p2: 'number'=0x133p3: 'tries'=0x0* time between wait #1 and #2: 1.586255 sec2.       event: 'latch: shared pool'time waited: 0.000032 secwait id: 182             p1: 'address'=0x6010a890p2: 'number'=0x133p3: 'tries'=0x0* time between wait #2 and #3: 0.133830 sec3.       event: 'latch: shared pool'time waited: 0.000114 secwait id: 181             p1: 'address'=0x6010a890p2: 'number'=0x133p3: 'tries'=0x0}Chain 1 Signature: 
Chain 1 Signature Hash: 0x673a0128

–对systemstate 没发现可疑信息
[oracle@dev-db ~]$ awk -f ass109.awk /oracle/diag/rdbms/ANBOB/ANBOB/trace/ANBOB_ora_23020.trc

— 奇怪为什么会发生在latch:shared pool上? 应该是sql解析和shared pool相关的事件，随后结束delete，做10046 观察究竟

sys@ANBOB>oradebug setmypid;
Statement processed.

sys@ANBOB>oradebug event 10046 trace name context forever,level 12
Statement processed.

sys@ANBOB>delete bjhr.doctor_exam_member;

92102 rows deleted.

sys@ANBOB>oradebug tracefile_name
/u01/app/oracle/diag/rdbms/anbob/anbob/trace/anbob_ora_7784.trc
sys@ANBOB>oradebug event 10046 trace name context off;
Statement processed.

— 格式化trace，终于发现了答案.

delete bjhr.doctor_exam_member
call     count       cpu    elapsed       disk      query    current        rows
------- ------  -------- ---------- ---------- ---------- ----------  ----------
Parse        1      0.00       0.00          0          0          0           0
Execute      1     47.30      48.39        201        222     657611       92102
Fetch        0      0.00       0.00          0          0          0           0
------- ------  -------- ---------- ---------- ---------- ----------  ----------
total        2     47.31      48.39        201        222     657611       92102Elapsed times include waiting on following events:Event waited on                             Times   Max. Wait  Total Waited----------------------------------------   Waited  ----------  ------------Disk file operations I/O                        2        0.00          0.00db file scattered read                         26        0.00          0.00db file sequential read                        24        0.00          0.00SQL*Net message to client                       1        0.00          0.00SQL*Net message from client                     1        0.00          0.00
********************************************************************************-- check deferred objectsselect pctfree_stg, pctused_stg, size_stg,initial_stg, next_stg, minext_stg, maxext_stg, maxsiz_stg, lobret_stg,mintim_stg, pctinc_stg, initra_stg, maxtra_stg, optimal_stg, maxins_stg,frlins_stg, flags_stg, bfp_stg, enc_stg,cmpflag_stg, cmplvl_stg
fromdeferred_stg$  where obj# =:1********************************************************************************
select /*+ all_rows */ count(1)
from"BJHR"."RESULT_NOTIFICATION_RECORD" where "DOCTOR_EXAM_MEMBER_ID" = :1call     count       cpu    elapsed       disk      query    current        rows
------- ------  -------- ---------- ---------- ---------- ----------  ----------
Parse        1      0.00       0.00          0          0          0           0
Execute  92102     11.31      11.34          0          0          0           0
Fetch    92102      0.63       0.64          0          0          0       92102
------- ------  -------- ---------- ---------- ---------- ----------  ----------
total   184205     11.95      11.99          0          0          0       92102Misses in library cache during parse: 1
Misses in library cache during execute: 1
Optimizer mode: ALL_ROWS
Parsing user id: SYS   (recursive depth: 1)
Number of plan statistics captured: 1Rows (1st) Rows (avg) Rows (max)  Row Source Operation
---------- ---------- ----------  ---------------------------------------------------1          1          1  SORT AGGREGATE (cr=0 pr=0 pw=0 time=43 us)0          0          0   TABLE ACCESS FULL RESULT_NOTIFICATION_RECORD (cr=0 pr=0 pw=0 time=12 us cost=3 size=5 card=1)Elapsed times include waiting on following events:Event waited on                             Times   Max. Wait  Total Waited----------------------------------------   Waited  ----------  ------------latch: shared pool                              2        0.00          0.00********************************************************************************
select /*+ all_rows */ count(1)
from"BJHR"."DOCTOR_EXAM_RESULT" where "DOCTOR_EXAM_MEMBER_ID" = :1call     count       cpu    elapsed       disk      query    current        rows
------- ------  -------- ---------- ---------- ---------- ----------  ----------
Parse        1      0.00       0.00          0          0          0           0
Execute  92102      6.97       7.11          0          0          0           0
Fetch    92102   1012.96    1016.14          0  566243096      92102       92102
------- ------  -------- ---------- ---------- ---------- ----------  ----------
total   184205   1019.93    1023.25          0  566243096      92102       92102Rows (1st) Rows (avg) Rows (max)  Row Source Operation
---------- ---------- ----------  ---------------------------------------------------1          1          1  SORT AGGREGATE (cr=6148 pr=0 pw=0 time=30196 us)0          0          0   TABLE ACCESS FULL DOCTOR_EXAM_RESULT (cr=6148 pr=0 pw=0 time=30184 us cost=1647 size=5 card=1)********************************************************************************
OVERALL TOTALS FOR ALL RECURSIVE STATEMENTScall     count       cpu    elapsed       disk      query    current        rows
------- ------  -------- ---------- ---------- ---------- ----------  ----------
Parse       39      0.00       0.01          0          0          0           0
Execute 184248     18.29      18.46          0          0          0           0
Fetch   184276   1013.60    1016.79          0  566243218      92102      184238
------- ------  -------- ---------- ---------- ---------- ----------  ----------
total   368563   1031.90    1035.27          0  566243218      92102      1842381129  elapsed seconds in trace file.

TIP:
在删除doctor_exam_member表时，检查了他的所有参照表(子表)，然后对doctor_exam_member表的每次记录都要去参照表查询是否存在，此时刚好参考表的外键列上并无索引，导致每一行记录都会导致FTS(full table scan),这也是查询v$session_event时偶尔出现latch: CBC (hot block)的原因。

你可能疑问子表数据都delete了为什么还查询这么久?我做个小测试

sys@ORA10GR2>select count(*) from bjhr_dev.DOCTOR_EXAM_RESULT;
COUNT(*)
——————–
0
sys@ORA10GR2>select bytes,blocks from dba_segments where segment_name=’DOCTOR_EXAM_RESULT’ and owner=’BJHR_DEV’;
BYTES BLOCKS
——————– ——————–
50331648 6144

sys@ORA10GR2>set autot trace stat
sys@ORA10GR2>select count(*) from bjhr_dev.DOCTOR_EXAM_RESULT where DOCTOR_EXAM_MEMBER_ID=1;

Statistics
———————————————————-
0 recursive calls
0 db block gets
6040 consistent gets
0 physical reads
0 redo size
514 bytes sent via SQL*Net to client
492 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
1 rows processed

sys@ORA10GR2>alter table bjhr_dev.doctor_exam_result enable row movement;
Table altered.
sys@ORA10GR2>alter table bjhr_dev.DOCTOR_EXAM_RESULT shrink space;
Table altered.
sys@ORA10GR2>alter table bjhr_dev.doctor_exam_result disable row movement;
Table altered.

sys@ORA10GR2>select bytes,blocks from dba_segments where segment_name=’DOCTOR_EXAM_RESULT’ and owner=’BJHR_DEV’;
BYTES BLOCKS
——————– ——————–
196608 24
sys@ORA10GR2>select count(*) from bjhr_dev.DOCTOR_EXAM_RESULT where DOCTOR_EXAM_MEMBER_ID=1;
Statistics
———————————————————-
0 recursive calls
0 db block gets
3 consistent gets
0 physical reads
0 redo size
514 bytes sent via SQL*Net to client
492 bytes received via SQL*Net from client
2 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
1 rows processed

TIP：
FTS查询会遍历表segment 已格式化过所有data block.

Summary:
在建有外键约束的子表列上需要创建索引，对子表全表删除时可以采用truncate 或delete(有外键不能truncate时)后对表进行shrink space操作，或删除父表前对子表的外键约束做Disable.