Oracle的db_files参数

相关参考：

How to increase db_files parameter? (Doc ID 2658128.1)

There are 2 limits, DB_FILES is a hard limit and MAXDATAFILES a soft limit.
这里有两个限制，DB_FILES是一个硬限制，MAXDATAFILES是一个软限制
DB_FILES is the limit on the total number of files associated with a particular INSTANCE of a database.

MAXDATAFILES is specified in the clause the last time CREATE DATABASE or CREATE CONTROLFILE was executed (database limit).
MAXDATAFILES在最后一次执行"CREATE DATABASE 或 CREATE CONTROLFILE" 的从句中指定

When MAXDATAFILES is reached, the controlfile will expand automatically (as long as there is disk space available) 
so that the data files section can accommodate more files.
Recreating the control file is not required to increase the MAXDATAFILES parameter.
当MAXDATAFILES达到预设值时，控制文件会自动扩大该值，重建控制文件不用修改该值

You can find these 2 values:
你可以通过以下语句查看这两个值
select value from v$parameter where name = 'db_files'; <<<<<<<DB_FILES
select records_total from v$controlfile_record_section where type = 'DATAFILE'; <<<<<<<<<< MAXDATAFILES

The default values for MAXDATAFILES is 30, the maximum value can be increased is 65534 (recreating the control file).
MAXDATAFILES可达到的最大值为65534

Note that within this there is a restriction of 1022 files per tablespace that cannot be changed.
单个表空间的限制是1022个文件。

If you decide to increase the limit of the number of files you should check also at OS level the maximum number of open files
也需要检查下OS层面的maximum number of open files
Here you have the recommended values:

Resource Shell Limit   Resource   Soft Limit      Hard Limit

--------------------   --------   -------------   ----------

Open file descriptors  nofile     at least 1024   at least 65536

具体限制还有

Database files

Maximum per database

65533

Database files的最大值参考：https://docs.oracle.com/cd/E11882_01/server.112/e40402/limits002.htm#REFRN0042
https://docs.oracle.com/en/database/oracle/oracle-database/19/cwhpx/checking-resource-limits-for-oracle-software-installation-users.html#GUID-293874BD-8069-470F-BEBF-A77C06618D5A

 DB_FILES设置过大，会浪费过多内存

1）以下初始参数会影响PGA的内存分配：
OPEN_LINKS
DB_FILES
LOG_FILES

2）DB_FILES initialization parameter indicates amount of SGA space to reserve for datafile information
https://www.quora.com/How-do-you-control-number-of-Datafiles-one-can-have-in-an-Oracle-database
https://www.dba-oracle.com/t_grid_rac_process_global_area.htm