Chensq's BLOG 简洁，高效

db_file_multiblock_read_count参数，都知道适用于全表扫描。其实，它也适用于快速全索引扫描(fast full index scan,FFS)：

PARSING IN CURSOR #1 len=68 dep=0 uid=28 oct=3 lid=0 tim=5349751183 hv=2771156860 ad=’22b43514′ sqlid=’d8kd6wukkszvw’
select /*+ index_ffs(test) */count(1) from test where object_id=1992
END OF STMT
PARSE #1:c=31250,e=176574,p=16,cr=68,cu=0,mis=1,r=0,dep=0,og=1,plh=2153817729,tim=5349751180
EXEC #1:c=0,e=24,p=0,cr=0,cu=0,mis=0,r=0,dep=0,og=1,plh=2153817729,tim=5349751270
WAIT #1: nam=’SQL*Net message to client’ ela= 4 driver id=1111838976 #bytes=1 p3=0 obj#=531 tim=5349751302
WAIT #1: nam=’db file sequential read’ ela= 14866 file#=4 block#=26910 blocks=1 obj#=18547 tim=5349766216
WAIT #1: nam=’db file scattered read’ ela= 16056 file#=4 block#=26911 blocks=128 obj#=18547 tim=5349782560
WAIT #1: nam=’db file scattered read’ ela= 21372 file#=4 block#=27039 blocks=128 obj#=18547 tim=5349809679
WAIT #1: nam=’db file scattered read’ ela= 22741 file#=4 block#=27167 blocks=128 obj#=18547 tim=5349838145
WAIT #1: nam=’db file scattered read’ ela= 21290 file#=4 block#=27295 blocks=128 obj#=18547 tim=5349865178
WAIT #1: nam=’db file scattered read’ ela= 21298 file#=4 block#=27423 blocks=128 obj#=18547 tim=5349892200
WAIT #1: nam=’db file scattered read’ ela= 22591 file#=4 block#=27551 blocks=128 obj#=18547 tim=5349920638
WAIT #1: nam=’db file scattered read’ ela= 21314 file#=4 block#=27679 blocks=128 obj#=18547 tim=5349947693
WAIT #1: nam=’db file scattered read’ ela= 21314 file#=4 block#=27807 blocks=128 obj#=18547 tim=5349974721
WAIT #1: nam=’db file scattered read’ ela= 22720 file#=4 block#=27935 blocks=128 obj#=18547 tim=5350003190

*** 2010-05-08 23:04:39.343
WAIT #1: nam=’db file scattered read’ ela= 18732 file#=4 block#=28063 blocks=106 obj#=18547 tim=5350027618
WAIT #1: nam=’db file scattered read’ ela= 24664 file#=4 block#=28189 blocks=128 obj#=18547 tim=5350057042
WAIT #1: nam=’db file scattered read’ ela= 22965 file#=4 block#=28317 blocks=128 obj#=18547 tim=5350085459
WAIT #1: nam=’db file scattered read’ ela= 21677 file#=4 block#=28445 blocks=128 obj#=18547 tim=5350112510
WAIT #1: nam=’db file scattered read’ ela= 21605 file#=4 block#=28573 blocks=128 obj#=18547 tim=5350139552
WAIT #1: nam=’db file scattered read’ ela= 21748 file#=4 block#=28701 blocks=128 obj#=18547 tim=5350166609
WAIT #1: nam=’db file scattered read’ ela= 23075 file#=4 block#=28829 blocks=128 obj#=18547 tim=5350195055
WAIT #1: nam=’db file scattered read’ ela= 21698 file#=4 block#=28957 blocks=128 obj#=18547 tim=5350222109
WAIT #1: nam=’db file scattered read’ ela= 21614 file#=4 block#=29085 blocks=128 obj#=18547 tim=5350249129
WAIT #1: nam=’db file scattered read’ ela= 6701 file#=4 block#=29213 blocks=51 obj#=18547 tim=5350261047

www.ads1st.com show parameter count

NAME                                 TYPE        VALUE
———————————— ———– ——————
active_instance_count                integer
cpu_count                            integer     2
db_file_multiblock_read_count        integer     256
www.ads1st.com alter system set db_file_multiblock_read_count=128;

系统已更改。

已用时间:  00: 00: 00.06

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