Oracel 19c Alert日志中的Creating new log segment

现象描述：

ORCL(3):Closing scheduler window

ORCL(3):Closing Resource Manager plan via scheduler window

Creating new log segment:

ORCL(3):Oracle Database 19c Enterprise Edition Release 19.0.0.0.0 - Production

Version 19.16.0.0.0.

ORCL(3):ORACLE_HOME: /u01/app/oracle/product/19.3.0/db

ORCL(3):System name: Linux

ORCL(3):Node name: zijindb1

ORCL(3):Release: 3.10.0-1160.el7.x86_64

ORCL(3):Version: #1 SMP Tue Aug 18 14:50:17 EDT 2020

ORCL(3):Machine: x86_64

ORCL(3):Using parameter settings in client-side pfile

ORCL(3):System parameters with non-default values:

ORCL(3): processes = 6400

ORCL(3): sessions = 9680

ORCL(3): use_large_pages = "ONLY"

ORCL(3): nls_language = "AMERICAN"

ORCL(3): nls_territory = "AMERICA"

ORCL(3): sga_target = 0

ORCL(3): control_files = "+DATADG/ORCL/CONTROLFILE/current.702.1112359937"

ORCL(3): control_files = "+DATADG/ORCL/CONTROLFILE/current.669.1112359937"

ORCL(3): db_file_name_convert = "/oradata/ORCLdg"

ORCL(3): db_file_name_convert = "+DATADG/ORCL"

ORCL(3): db_file_name_convert = "/u01/app/oracle/oradata/ORCL"

ORCL(3): db_file_name_convert = "+DATADG/ORCL"

ORCL(3): log_file_name_convert = "/oradata/ORCLdg/onlinelog"

ORCL(3): log_file_name_convert = "+DATADG/ORCL/ONLINELOG"

ORCL(3): log_file_name_convert = "/u01/app/oracle/flash_recovery_area/ORCL/onlinelog"

ORCL(3): log_file_name_convert = "+DATADG/ORCL/ONLINELOG"

ORCL(3): db_block_size = 8192

ORCL(3): compatible = "19.0.0"

ORCL(3): log_archive_dest_1 = "LOCATION=+ARCH VALID_FOR=(ALL_LOGFILES,ALL_ROLES) DB_UNIQUE_NAME=ORCL"

ORCL(3): log_archive_dest_2 = "SERVICE=ORCLdg ASYNC VALID_FOR=(ONLINE_LOGFILES,PRIMARY_ROLE) DB_UNIQUE_NAME=ORCLdg"

ORCL(3): log_archive_dest_3 = "SERVICE=ORCLdg1 ASYNC VALID_FOR=(ONLINE_LOGFILES,PRIMARY_ROLE) DB_UNIQUE_NAME=ORCLdg1"

ORCL(3): log_archive_dest_state_2 = "ENABLE"

ORCL(3): log_archive_dest_state_3 = "ENABLE"

ORCL(3): fal_server = "ORCLdg,ORCLdg1"

ORCL(3): log_archive_config = "DG_CONFIG=(ORCL,ORCLdg,ORCLdg1)"

ORCL(3): cluster_database = TRUE

ORCL(3): db_create_file_dest = "+DATADG"

ORCL(3): db_recovery_file_dest = "+DATADG"

ORCL(3): db_recovery_file_dest_size= 100G

ORCL(3): standby_file_management = "AUTO"

ORCL(3): thread = 1

ORCL(3): undo_tablespace = "UNDOTBS1"

ORCL(3): instance_number = 1

ORCL(3): remote_login_passwordfile= "EXCLUSIVE"

ORCL(3): dispatchers = "(PROTOCOL=TCP) (SERVICE=ORCLXDB)"

ORCL(3): local_listener = " (ADDRESS=(PROTOCOL=TCP)(HOST=192.168.3.1)(PORT=1521))"

ORCL(3): audit_file_dest = "/u01/app/oracle/admin/ORCL/adump"

ORCL(3): audit_trail = "DB"

ORCL(3): db_name = "ORCL"

ORCL(3): open_cursors = 500

ORCL(3): pga_aggregate_target = 24192M

ORCL(3): diagnostic_dest = "/u01/app/oracle"

ORCL(3): enable_pluggable_database= TRUE

现象分析：

该现象为12c后的一个新的情况，Alert日志就分为两种格式存储在文件系统上了，一种是老的文本格式的Alert日志，可用于直接查看分析问题。另一种是XML文件格式，用于EM等软件分析问题。默认情况下当XML文件的大小超过10M的时候Oracle会自动创建一个新的文件log.xml(监听日志也是如此)，而老的文件会以log_.xml的方式命名。 这些数据库参数和补丁的信息显示就发生在XML文件切换时。Oracle将log.xml文件也看做一个segment，在新生成的XML文件中，数据库启动时的参数和补丁信息被dump到新的log.xml文件中。所以Alert日志中的Creating new log segment指的是正在创建新的log.xml段，这个过程是Oracle的正常“工作”。

可用操作：

这种行为只有在Alert日志信息生成非常频繁的情况下可能会成为一个问题。文档里也提到了一个Bug，就是当数据库开启supplemental logging后，会产生大量的Alert日志，这样系统生成新的log.xml文件就很频繁，这时如果再加上系统需要dump这些启动参数和补丁的信息，log.xml文件就会切换的更频繁或者产生其它的问题。

然而，如果你不想让这些信息出现在Alert日志中，那么可以采用下面的方法进行屏蔽。不过隐含参数除非有必要，否则一律不推荐修改。

1.禁止参数信息dump至Alert日志中

_log_segment_dump_parameter=FALSE

2.禁止补丁信息dump至Alert日志中
_log_segment_dump_patch=FALSE