提高oracle数据库的查询统计速度

大型数据库系统中往往要用到查询统计，但是对于数据量大的系统，用户在进行复杂的查询统计时往往感到速度很慢，不能满足应用要求，这就要求我们在设计数据库系统时进行合理设置，提高查询统计的速度。本文结合笔者的项目开发经验，阐述具体的设置方法。

以oracle7.33数据库系统为例，我们在开发大型oracle数据库系统时结合项目的特点，本着安全、高效的原则对数据库进行了一些物理设计，从而大大提高了数据库的查询统计速度。总结为如下几点：

1）扩大数据表空间到500m，用于存放本系统的数据；

2）段盘区的初始大小为10k，增长大小为10k，增长幅度为1；

3）用户临时空间增大40m；

4）系统临时表空间和回滚段表空间增大40m，并且新建4个回滚段；

5）需要经常联结查询，而且数据量又大的库存表、名录表、收发料表放在一簇内；

6）提供定时备份，备份文件放在另外的机器上。

设置数据表空间的sql语句如下：

create tablespace wxgl_data1 datafile ''wxgl_data1.ora'' size 500m online;

增加系统临时表空间和回滚段表空间的sql语句如下：

alter tablespace temporary_data add datafile ''tmp2orcl.ora'' size 40m;alter tablespace rollback_data  add datafile ''rbs2orcl.ora'' size 40m;

将数据空间设置在指定的数据文件的sql语句如下：

create user zbgl identified by zbgl;grant dba to zbgl;alter user zbgl default tablespace wxgl_data1 temporary tablespace temporary_data;

设置五个回滚段的sql语句如下：

select segment_name from dba_rollback_segs where initial_extent < 512000 anduppper(owner) = ''public'';select upper(status) from dba_rollback_segs where upper(segment_name) = ''''alter rollback segment rb1 offline;alter rollback segment rb2 offline;alter rollback segment rb3 offline;alter rollback segment rb4 offline;alter rollback segment rb5 offline;drop rollback segment rb1;drop rollback segment rb2;drop rollback segment rb3;drop rollback segment rb4;drop rollback segment rb5;create public rollback segment rb1 tablespace rollback_data   storage (initial 512000 next 512000 maxextents 121);create public rollback segment rb2 tablespace rollback_data   storage (initial 512000 next 512000 maxextents 121);create public rollback segment rb3 tablespace rollback_data   storage (initial 512000 next 512000 maxextents 121);create public rollback segment rb4 tablespace rollback_data   storage (initial 512000 next 512000 maxextents 121);create public rollback segment rb5 tablespace rollback_data   storage (initial 512000 next 512000 maxextents 121);alter rollback segment rb1 online;alter rollback segment rb2 online;alter rollback segment rb3 online;alter rollback segment rb4 online;alter rollback segment rb5 online;commit;

将数据量大的库存表等放在一簇内的sql语句如下：

kcb=''create table qc_kcb( ''         +'' cknm      number(8)  ,''         +'' qcnm      number(10) ,''         +'' ckkc      number(12,2),''         +'' snckkc    number(12,2),''         +'' ldj       number(12,2),''         +'' bz        varchar(100),''         +'' primary key(cknm,qcnm))''         +'' tablespace wxgl_data1 '' ;（大数据量的库存表等放在wxgl_data1)qcfl = ''create table qc_qcfl ''     + ''(flbh   number(2) primary key,''     + '' flmc   varchar(20) ''     + '' ) ''     +'' tablespace wxgl_data2 '' ;(其他表放在wxgl_data2）

系统的基础数据库存表、名录表大约有数据80m；一个单位一般每年收发300次，收发料单大约有数据50m；系统冗余数据100m，系统辅助数据10m；因此，系统总共需要空间大约是240m，现在系统开辟数据空间500m，完全满足存储要求。由于系统使用了冗余数据，在查询常用数据时，避免了多表联结查询的情况，这样，虽然使用了更多的存储空间，但查询效率大幅度提高；同时，系统将需要经常联结查询的数据放在一簇，即将存放这些数据的空间在物理上相邻，这样也使查询速度大大提高。

另外在oracle7.33数据库的database目录下有一个initorcl.ora文件，改变其中的设置也可以提高查询统计速度。该文件的内容如下：

## $header: init.ora 1.2 94/10/18 16:12:36 gdudey osd<desktop/netware> $ init.ora copyr (c) 1991 oracle################################################################################ example init.ora file## this file is provided by oracle corporation to help you customize# your rdbms installation for your site.  important system parameters# are discussed, and example settings given.## some parameter settings are generic to any size installation.# for parameters that require different values in different size# installations, three scenarios have been provided: small, medium# and large.  any parameter that needs to be tuned according to # installation size will have three settings, each one commented# according to installation size.## use the following table to approximate the sga size needed for the# three scenarious provided in this file:##                     -------installation/database size------#                      small           medium           large#  block         2k    4500k            6800k           17000k#  size          4k    5500k            8800k           21000k## to set up a database that multiple instances will be using, place# all instance-specific parameters in one file, and then have all# of these files point to a master file using the ifile command.# this way, when you change a public# parameter, it will automatically change on all instances.  this is # necessary, since all instances must run with the same value for many# parameters. for example, if you choose to use private rollback segments, # these must be specified in different files, but since all gc_* # parameters must be the same on all instances, they should be in one file.## instructions: edit this file and the other init files it calls for# your site, either by using the values provided here or by providing# your own.  then place an ifile= line into each instance-specific# init file that points at this file.###############################################################################db_name = oracledb_files = 20control_files = c:\orawin95\database\ctl1orcl.oracompatible = 7.3.0.0.0db_file_multiblock_read_count =  8 # initial# db_file_multiblock_read_count = 8                                   # small  # db_file_multiblock_read_count = 16                                  # medium # db_file_multiblock_read_count = 32                                  # large  db_block_buffers =  200                           # initial# db_block_buffers = 200                                              # small  # db_block_buffers = 550                                              # medium # db_block_buffers = 3200                                             # large  shared_pool_size =  3500000                           # initial# shared_pool_size = 3500000                                          # small# shared_pool_size = 6000000                                          # medium# shared_pool_size = 9000000                                          # largelog_checkpoint_interval = 10000processes =  50                                         # initial# processes = 50                                                      # small  # processes = 100                                                     # medium # processes = 200                                                     # large  dml_locks =  100                                         # initial# dml_locks = 100                                                     # small  # dml_locks = 200                                                     # medium # dml_locks = 500                                                     # largelog_buffer =  8192                                       # initial# log_buffer = 8192                                                   # small# log_buffer = 32768                                                  # medium# log_buffer = 163840                                                 # largesequence_cache_entries =  10               # initial# sequence_cache_entries = 10                                         # small  # sequence_cache_entries = 30                                         # medium # sequence_cache_entries = 100                                        # large  sequence_cache_hash_buckets =  10     # initial# sequence_cache_hash_buckets = 10                                    # small  # sequence_cache_hash_buckets = 23                                    # medium # sequence_cache_hash_buckets = 89                                    # large  # audit_trail = true            # if you want auditing# timed_statistics = true       # if you want timed statisticsmax_dump_file_size = 10240      # limit trace file size to 5 meg each              # log_archive_start = true      # if you want automatic archivinglog_archive_dest=%oracle_home%\database\archive# define directories to store trace and alert filesbackground_dump_dest=%rdbms73%\traceuser_dump_dest=%rdbms73%\tracedb_block_size = 2048snapshot_refresh_processes = 1remote_login_passwordfile = shared

可以修改该文件的db_file_multiblock_read_count，db_block_buffers，shared_pool_size，processes ，log_buffer，sequence_cache_entries，sequence_cache_hash_buckets等项（文件中均有提示），根据需要和系统使用的数据库服务器的特点适当改大数值，可以提高查询统计速度。这里要注意的是，必须将 log_archive_start = true 项改为false，设置才能生效。

本文介绍的oracle数据库设置方法均在用户实际使用中经过了严格测试，证明是有效和实用的。