常用参数修改命令

# 修改最大连接数
```sql
sqlplus /nolog
conn / as sysdba;
alter system set processes = 1000 scope = spfile;
shutdown immediate;
startup;
```
# 修改归档日志大小

```sql
sqlplus /nolog
conn / as sysdba;
startup nomount;
show parameter db_recovery_file_dest;
alter system set db_recovery_file_dest_size=20G scope=both;
shutdown immediate
startup;
```
# 统计信息

```sql
--用JHEMR用户 不用 as sysdba;
exec DBMS_STATS.GATHER_SCHEMA_STATS(ownname =>'JHEMR',estimate_percent=>10,method_opt=>'FOR ALL COLUMNS SIZE AUTO',degree=>4);
exec DBMS_STATS.GATHER_SCHEMA_STATS(ownname =>'REPORT',estimate_percent=>10,method_opt=>'FOR ALL COLUMNS SIZE AUTO',degree=>4);
exec DBMS_STATS.GATHER_SCHEMA_STATS(ownname =>'JHCDR',estimate_percent=>10,method_opt=>'FOR ALL COLUMNS SIZE AUTO',degree=>4);
exec DBMS_STATS.GATHER_SCHEMA_STATS(ownname =>'JHFILE',estimate_percent=>10,method_opt=>'FOR ALL COLUMNS SIZE AUTO',degree=>4);

--系统统计信息
--统计信息
select * from sys.aux_stats$;
--收集非工作量统计信息
exec dbms_stats.gather_system_stats(gathering_mode => 'NOWORKLOAD');
--收集工作量统计信息
begin
  dbms_stats.gather_system_stats(gathering_mode => 'interval',
                                 interval       => 30);
end;
```

# 清理执行SQL执行计划

```sql
--第一步：查询SQL的ID
select sql_id, first_load_time from v$sql where sql_text like 'select * from scott.dept%';

--第二步：查询SQL的ADDRESS，HASH_VALUE，SQL_TEXT
select address, hash_value, sql_text from v$sqlarea where sql_id='3nvuzqdn6ry6x';

--第三步：根据ADDRESS，HASH_VALUE清理执行计划
exec dbms_shared_pool.purge('00000000968ED510,1751906525','C');
```