Oracle event 之13740

今天在一套测试库启动过程中发现如下信息，这在之前没有看到过，稍微研究一下

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Fri Jan  7 14:01:02 2011
Starting ORACLE instance (normal)
LICENSE_MAX_SESSION = 0
LICENSE_SESSIONS_WARNING = 0
Picked latch-free SCN scheme 3
Using LOG_ARCHIVE_DEST_1 parameter default value as /ora10/oracle/product/10.2.0/db_1/dbs/arch
Autotune of undo retention is turned on.
IMODE=BR
ILAT =10
LICENSE_MAX_USERS = 0
SYS auditing is disabled
ksdpec: called for event 13740 prior to event group initialization
Starting up ORACLE RDBMS Version: 10.2.0.4.0.

event 13740在metalink解释为，详见doc id 342505.1

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"Event 13740 is an event id used when tracing ASH. It is detected when mapping the SGA during
startup, so this message is only informational. There is no need to worry. There is no way
currently in the code of disabling this message"

我们可以查看一下ash buffer在shared pool中的情况，刚好为8M

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SQL> select * from v$sgastat  where upper(name) like 'ASH%';

POOL         NAME                            BYTES
------------ -------------------------- ----------
shared pool  ASH buffers                   8388608

据说此大小和cpu个数有关，4*2M，目前系统中cpu核数为4颗

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SQL> show parameter cpu

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
cpu_count                            integer     4
parallel_threads_per_cpu             integer     2

在alert日志中也有所体现

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where NUMA PG = 1, CPUs = 4

附ash的一些隐含参数

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_ash_sampling_interval                        1000                 Time interval between two successive Active Sessio
_ash_size                                     1048618              To set the size of the in-memory Active Session Hi
_ash_enable                                   TRUE                 To enable or disable Active Session sampling and f
_ash_disk_write_enable                        TRUE                 To enable or disable Active Session History flushi
_ash_disk_filter_ratio                        10                   Ratio of the number of in-memory samples to the nu
_ash_eflush_trigger                           66                   The percentage above which if the in-memory ASH is
_ash_sample_all                               FALSE                To enable or disable sampling every connected sess
_ash_dummy_test_param                         0                    Oracle internal dummy ASH parameter used ONLY for