其实随着技术的发展，大表和小表的概念也不停的变化的。
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一般而言，大表的记录数超过100万吧
记录数超过1000万条，为超大表，一般就要分区了，否则性能没办法保证的。
1. 推荐一个使用平均值估算表空间的脚本：
--不适用windows
with t1 as (
select ss.run_time,ts.name,
decode((round(su.tablespace_usedsize*dt.block_size/1024/1024,2)),null,0,(round(su.tablespace_usedsize*dt.block_size/1024/1024,2))) used_size_mb
from
dba_hist_tbspc_space_usage su,
(select trunc(BEGIN_INTERVAL_TIME) run_time,max(snap_id) snap_id from dba_hist_snapshot
group by trunc(BEGIN_INTERVAL_TIME) ) ss,
v$tablespace ts,
dba_tablespaces dt
where su.snap_id = ss.snap_id
and su.tablespace_id = ts.ts#
and ts.name NOT LIKE '%TEMP%'
and ts.name NOT LIKE '%UNDO%'
and ts.name = dt.tablespace_name order by 2,1),
t2 as (
select e.run_time,e.name,e.used_size_mb,e.used_size_mb - b.used_size_mb growth
from t1 e, t1 b
where e.name = b.name and e.run_time = b.run_time +1),
t5 as (select a.TABLESPACE_NAME,
a.FILE_NAME,
a.FILE_ID,
a.BYTES,
a.AUTOEXTENSIBLE,
a.ONLINE_STATUS,
a.MAXBYTES,
case
when a.AUTOEXTENSIBLE = 'YES' and
a.ONLINE_STATUS not in ('OFFLINE', 'SYSOFF') then
nvl(a.MAXBYTES, 0)
else
nvl(a.BYTES, 0)
end file_max_size
from dba_data_files a
where a.tablespace_name NOT LIKE '%TEMP%'
and a.tablespace_name NOT LIKE '%UNDO%'
),
t3 as (
select tsz.tablespace_name,
tsz.alloc_size_mb,ave.avg_growth_per_day_mb,ave.avg_growth_per_day_mb*90 projected_growth_for_3mths_mb
from
(select tablespace_name, round(sum(file_max_size)/1024/1024,2) alloc_size_mb from t5 group by tablespace_name) tsz,
(select name,decode(round(avg(growth),2),null,0.11,0,0.11, round(avg(growth),2)) avg_growth_per_day_mb from t2 group by name) ave
where tsz.tablespace_name = ave.name),
t6 as (select
d.tablespace_name tablespace_name,
round((d.sumbytes/1024/1024),2) total_g ,
round(decode(f.sumbytes,null,0,f.sumbytes)/1024/1024,2) free,
round(((d.sumbytes-f.sumbytes)/1024/1024),6) size_could_be_used,
round((d.sumbytes-decode(f.sumbytes,null,0,f.sumbytes))*100/d.sumbytes,2) used_pct,
(100-round((d.sumbytes-decode(f.sumbytes,null,0,f.sumbytes))*100/d.sumbytes,2))*round((d.sumbytes/1024/1024),2) real_free
from
(select
tablespace_name, sum(bytes) sumbytes
from dba_free_space group by tablespace_name) f,
(select tablespace_name, sum(bytes) sumbytes
from dba_data_files group by tablespace_name) d
where f.tablespace_name(+) = d.tablespace_name)
select t4.tablespace_name,decode(t3.alloc_size_mb,null,0,t3.alloc_size_mb) alloc_sz_mb,
--t6.real_free/round(decode(avg_growth_per_day_mb,null,365,0,365,(t3.avg_growth_per_day_mb)),2) Days_To_Be_Used,
((100-decode(round(t6.size_could_be_used*100/t3.alloc_size_mb,2),null,0,round(t6.size_could_be_used*100/t3.alloc_size_mb,2)))/100*t3.alloc_size_mb)/avg_growth_per_day_mb Days_To_Be_Used,
round(t6.size_could_be_used*100/t3.alloc_size_mb,4) used_pct_auto,
t6.used_pct used_pct_real
from t3,t6,
(select a.tablespace_name,
round(a.bytes/1024/1024/1024,2) alloc,
round(c.bytes/1024/1024/1024,2) free
from sys.sm$ts_avail a,
sys.sm$ts_free c
where a.tablespace_name = c.tablespace_name(+)
and a.tablespace_name NOT LIKE '%TEMP%'
and a.tablespace_name NOT LIKE '%UNDO%'
) t4
where t4.tablespace_name = t3.tablespace_name(+)
and t4.tablespace_name = t6.tablespace_name(+)
--and ((100-decode(round(t6.size_could_be_used*100/t3.alloc_size_mb,2),null,0,round(t6.size_could_be_used*100/t3.alloc_size_mb,2)))/100*t3.alloc_size_mb)/avg_growth_per_day_mb =30
and ((100-decode(round(t6.size_could_be_used*100/t3.alloc_size_mb,2),null,0,round(t6.size_could_be_used*100/t3.alloc_size_mb,2)))/100*t3.alloc_size_mb)/avg_growth_per_day_mb=0
order by 1;
2. 通过线性回归参数预测未来使用量（待补充）：
先预估数据量，然后用数据量乘上总字段长度，可以大致预估出表大小
通常对于小表，Oracle建议通过全表扫描进行数据访问，对于大表则应该通过索引以
Oracle通过一个内部参数_small_table_threshold来定义大表和小表的界限。
电脑电压是怎么回事~！
自考中有拉长线的说法,什么是拉长线?
我们之前有遇到过这样的情况，是采用分表来处理的，有一个实时表，仅存放本月数据（实时增加的），历史数据按月分表存储（每个表数据量大概是一百万到400万），分表命名根据时间设定一定规则（目的是为了能动态查询）
