讲解Oracle SGA 的分配

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ORACLE 8.0.X 版本BAXTechFeel
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SGA=((db_block_buffers * block size)+(shared_pool_size+large_pool_size+log_buffers)+1MBBAXTechFeel
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ORACLE 8.1.X 版本BAXTechFeel
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SGA=((db_block_buffers * block size)+(shared_pool_size+large_pool_size+java_pool_size+log_buffers)+1MBBAXTechFeel
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理论上SGA可占OS系统物理内存的1/2——1/3，我们可以根据需求调整BAXTechFeel
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我推荐SGA=0.45*(OS RAM)BAXTechFeel
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假设服务器运行ORACLE 8.1.X 版本, OS系统内存为2G MEM, db_block_size 是8192 bytes, BAXTechFeel
除了运行ORACLE数据库外, 没有其它的应用程序或服务器软件.BAXTechFeel
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这样SGA合计约为921M ( 0.45*2048M ), BAXTechFeel
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设shared_pool_size 250M (250*1024*1024 bytes)BAXTechFeel
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设database buffer cache 620M (79360*8192 bytes)BAXTechFeel
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initorasid.ora文件里具体各参数如下:BAXTechFeel
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shared_pool_size = 262144000BAXTechFeel
# 250 MBAXTechFeel
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db_block_buffers = 79360BAXTechFeel
# 620 MBAXTechFeel
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log_buffer = 524288BAXTechFeel
# 512k (128K*CPU个数)BAXTechFeel
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large_pool_size = 31457280BAXTechFeel
# 30 MBAXTechFeel
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java_pool_size = 20971520BAXTechFeel
# 20 MBAXTechFeel
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sort_area_size = 524288BAXTechFeel
# 512k (65k--2M)BAXTechFeel
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sort_area_retained_size = 524288BAXTechFeel
# MTS 时 sort_area_retained_size = sort_area_sizeBAXTechFeel

SUN Solaris里/etc/system文件里的几个参数同样跟内存分配有关

ORACLE安装时缺省的设置:	建议修改的设置:
set shmsys:shminfo_shmmax=4294967295 BAXTechFeel set shmsys:shminfo_shmmin=1 BAXTechFeel set shmsys:shminfo_shmmni=100 BAXTechFeel set shmsys:shminfo_shmseg=15 BAXTechFeel set semsys:seminfo_semmns=200 BAXTechFeel set semsys:seminfo_semmni=70 BAXTechFeel set ulimit=3000000	BAXTechFeel set semsys:seminfo_semmni=315BAXTechFeel set semsys:seminfo_semmsl=300BAXTechFeel set semsys:seminfo_semmns=630BAXTechFeel set semsys:seminfo_semopm=315BAXTechFeel set semsys:seminfo_semvmx=32767BAXTechFeel set shmsys:shminfo_shmmax=4294967295BAXTechFeel set shmsys:shminfo_shmmni=315BAXTechFeel set shmsys:shminfo_shmseg=10BAXTechFeel set shmsys:shminfo_shmmin=1

其中这些参数的含义

shmmax - 共享内存段的最大字节数，建议设大点，甚至可以大过物理内存的字节数BAXTechFeel
shmmin - 共享内存段的最小尺寸.BAXTechFeel
shmmni - 共享内存段的最大数目.BAXTechFeel
shmseg - 每个进程可分配的最大共享内存段数目.BAXTechFeel
shmall - 最大的并发共享内存段数目，比SGA还要大.BAXTechFeel
semmns - 信号灯的最大数量，跟ORACLE的PROCESS数有关.BAXTechFeel
semmsl - 每个信号灯集合中最多的信号灯数目.

关键字: Oracle,SGA,分配

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