PX Deq Credit: send blkd

在AWR报告中出现如下：

Top 5 Timed Events                                         Avg %Total
~~~~~~~~~~~~~~~~~~                                        wait   Call
Event                                 Waits    Time (s)   (ms)   Time Wait Class
―――――――――― ―――― ―――�C ―― ―― ―――-
cursor: pin S wait on X           6,618,147      70,770     11   38.4 Concurrenc
PX Deq Credit: send blkd            223,971      32,348    144   17.5      Other
db file sequential read           4,018,002      24,072      6   13.0   User I/O
latch: row cache objects            861,170      16,650     19    9.0 Concurrenc
CPU time                                          7,398           4.0

其中cursor: pin S wait on X和PX Deq Credit: send blkd，等待事件特别高，后者处理如下：

The wait events  “PX Deq Credit: need buffer”  and  “PX Deq Credit: send blkd” are occur when data or
messages are exchanged between process that are part of a px query..

Tips to Reduce Waits for “PX DEQ CREDIT SEND BLKD” at Database Level [ID 738464.1]
PURPOSE
――-
Provide some scripts for a DBA to check the degree of parallelism
on tables and indexes.

SCOPE & APPLICATION
――――――-
DBA’s, developer and Analysts.

SQL> conn /as sysdba
Connected to Oracle Database 10g Enterprise Edition Release 10.2.0.3.0
Connected as SYS

SQL>
SQL> select substr(name,1,30) Name , substr(value,1,5) Value
2  from v$parameter
3  where  name in  (‘parallel_threads_per_cpu’ , ‘cpu_count’ );

NAME                                                                             VALUE
――――――――――――――――――――――――――�C ―――――
cpu_count                                                                        16
parallel_threads_per_cpu                                                         2

SQL>
SQL> select * from (
2  select  substr(owner,1,15)  Owner  , ltrim(degree) Degree,
3          ltrim(instances)  Instances,
4          count(*)   “Num Tables”  , ‘Parallel’
5  from all_tables
6  where ( trim(degree) != ’1′ and trim(degree) != ’0′ ) or
7        ( trim(instances) != ’1′ and trim(instances) != ’0′ )
8  group by  owner, degree , instances
9  union
10  select  substr(owner,1,15) owner  ,  ’1′ , ’1′ ,
11           count(*)  , ‘Serial’
12  from all_tables
13  where ( trim(degree) = ’1′ or trim(degree) = ’0′ ) and
14        ( trim(instances) = ’1′ or trim(instances) = ’0′ )
15  group by  owner
16  )
17  order by owner;

OWNER                                         DEGREE                         INSTANCES                      Num Tables ‘PARALLEL’
――――――――――――――― ―――――――――― ―――――――――― ―――- ―――-
BACKUP                                        1                              1                                       1 Serial
CTXSYS                                        1                              1                                      37 Serial
DBSNMP                                        1                              1                                      21 Serial
DMSYS                                         1                              1                                       2 Serial
EXFSYS                                        1                              1                                      44 Serial
IGNITE                                        1                              1                                       2 Serial
IGNITE_C                                      1                              1                                       1 Serial
NETBEN                                        1                              1                                   14426 Serial
OLAPSYS                                       1                              1                                     126 Serial
OUTLN                                         1                              1                                       3 Serial
SORAC                                         1                              1                                      10 Serial
SYS                                           1                              1                                     742 Serial
SYSMAN                                        1                              1                                     340 Serial
SYSTEM                                        1                              1                                     141 Serial
TSMSYS                                        1                              1                                       1 Serial
WMSYS                                         1                              1                                      40 Serial
XDB                                           1                              1                                      11 Serial

17 rows selected

SQL>
SQL> select * from (
2  select  substr(owner,1,15) Owner  ,
3          substr(trim(degree),1,7) Degree ,
4          substr(trim(instances),1,9) Instances ,
5          count(*)   “Num Indexes”,
6          ‘Parallel’
7  from all_indexes
8  where ( trim(degree) != ’1′ and trim(degree) != ’0′ ) or
9        ( trim(instances) != ’1′ and trim(instances) != ’0′ )
10  group by  owner, degree , instances
11  union
12  select  substr(owner,1,15) owner  ,  ’1′ , ’1′ ,
13           count(*)  , ‘Serial’
14  from all_indexes
15  where ( trim(degree) = ’1′ or trim(degree) = ’0′ ) and
16        ( trim(instances) = ’1′ or trim(instances) = ’0′ )
17  group by  owner
18  )
19  order by owner;

OWNER                                         DEGREE                INSTANCES                   Num Indexes ‘PARALLEL’
――――――――――――――― ――――――― ――――――――― ―――�C ―――-
BACKUP                                        1                     1                                     1 Serial
CTXSYS                                        1                     1                                    46 Serial
DBSNMP                                        1                     1                                    10 Serial
DMSYS                                         1                     1                                     2 Serial
EXFSYS                                        1                     1                                    37 Serial
IGNITE_C                                      1                     1                                     1 Serial
NETBEN                                        1                     1                                 23563 Serial
NETBEN                                        DEFAULT               DEFAULT                              14 Parallel
OLAPSYS                                       1                     1                                   135 Serial
OUTLN                                         1                     1                                     3 Serial
SYS                                           1                     1                                   705 Serial
SYS                                           DEFAULT               DEFAULT                               1 Parallel
SYSMAN                                        1                     1                                   396 Serial
SYSTEM                                        1                     1                                   180 Serial
TSMSYS                                        1                     1                                     1 Serial
WMSYS                                         1                     1                                    57 Serial
XDB                                           1                     1                                    51 Serial

17 rows selected

SQL>
SQL> select  substr(t.owner,1,15) Owner  ,
2          t.table_name ,
3          substr(trim(t.degree),1,7) Degree ,
4          substr(trim(t.instances),1,9) Instances,
5          i.index_name ,
6          substr(trim(i.degree),1,7) Degree ,
7          substr(trim(i.instances),1,9) Instances
8  from all_indexes  i,
9       all_tables   t
10  where  ( trim(i.degree) !=  trim(t.degree)  or
11           trim(i.instances) !=  trim(t.instances)  ) and
12           i.owner = t.owner  and
13           i.table_name = t.table_name;

OWNER                                         TABLE_NAME                     DEGREE                INSTANCES                   INDEX_NAME                     DEGREE                INSTANCES
――――――――――――――― ―――――――――― ――――――― ――――――――― ―――――――――― ――――――― ―――――――――
SYS                                           UTL_RECOMP_SORTED              1                     1                           UTL_RECOMP_SORT_IDX1           DEFAULT               DEFAULT
NETBEN                                        NB_TRAN_24612                  1                     1                           PK_NB_TRAN_24612_1             DEFAULT               DEFAULT
NETBEN                                        MV_PAGE_24612                  1                     1                           IN_MV_PAGE_PERF_24612          DEFAULT               DEFAULT
NETBEN                                        MV_PAGE_1417                   1                     1                           IN_MV_PAGE_PERF_1417           DEFAULT               DEFAULT
NETBEN                                        NB_PAGE_24612                  1                     1                           IN_PAGE_TRANID_24612           DEFAULT               DEFAULT
NETBEN                                        NB_PAGE_24612                  1                     1                           IN_PAGE_PERF_24612             DEFAULT               DEFAULT
NETBEN                                        NB_PAGE_24612                  1                     1                           IN_PAGE_ERROR_24612            DEFAULT               DEFAULT
NETBEN                                        NB_PAGE_1417                   1                     1                           IN_PAGE_TRANID_1417            DEFAULT               DEFAULT
NETBEN                                        NB_PAGE_1417                   1                     1                           IN_PAGE_PERF_1417              DEFAULT               DEFAULT
NETBEN                                        NB_PAGE_1417                   1                     1                           IN_PAGE_ERROR_1417             DEFAULT               DEFAULT
NETBEN                                        NB_PAGE_23500                  1                     1                           IN_PAGE_ERROR_23500            DEFAULT               DEFAULT
NETBEN                                        NB_TRAN_1417                   1                     1                           IN_TRAN_PERF_1417              DEFAULT               DEFAULT
NETBEN                                        NB_PAGE_23500                  1                     1                           IN_PAGE_PERF_23500             DEFAULT               DEFAULT
NETBEN                                        NB_PAGE_23500                  1                     1                           IN_PAGE_TRANID_23500           DEFAULT               DEFAULT
NETBEN                                        NB_TRAN_22                     1                     1                           IN_TRAN_PERF_22                DEFAULT               DEFAULT

15 rows selected