數據庫出現hang住,我們看到process已經超了

進行hanganalyze文件問題收集，懷疑是並行出現了問題

這裏的通過sql_id看不到全部的sql_text，也是個問題，這個先解決首要問題，所以先忽略

The SQL Text Stored for a Create Table As Select (CTAS) Statement is Truncated to 20 Characters in View DBA_HIST_SQLTEXT (Doc ID 2039794.1)

我們發現cpu使用率很高，再通過hanganalyze文件分析並行，我們進一步查看數據庫並行的情況，parallel_max_servers

關於parallel_max_servers這個參數值的設置

th 11.2.0.2 there is a new method to compute the default for PARALLEL_MAX_SERVERS.

 

In the Oracle Rdbms Reference Guide we find:

parallel_max_servers = PARALLEL_THREADS_PER_CPU * CPU_COUNT * concurrent_parallel_users * 5

In the formula, the value assigned to concurrent_parallel_users running at the default degree of parallelism on an

instance is dependent on the memory management setting.

 - If automatic memory management is disabled (manual mode), then the value of concurrent_parallel_users is 1.

 - If PGA automatic memory management is enabled, then the value of concurrent_parallel_users is 2.

 - If global memory management or SGA memory target is used in addition to PGA automatic memory management,

   then the value of concurrent_parallel_users is 4.

The value is capped by processes -15 (this is true for versions prior 11.2.0.2 as well).

As example we have the following values

 

parallel_threads_per_cpu  = 2

cpu_count                 = 4

pga_aggregate_target      = 500M

sga_target                = 900M

processes                 = 150

 

parallel_max_servers = 2 * 4 * 4 * 5 = 160

parallel_max_servers = min( 150-15 , 160 ) = 135

So with these values we get a default of 135 for parallel_max_servers.

Note if the parallel_max_servers is reduced due to value of processes, then you see similar to the following in alert log (e.g. at instance start up):

Mon May 06 18:43:06 2013

Adjusting the default value of parameter parallel_max_servers

 

 

SQL>  show parameter cpu

 

NAME                                 TYPE        VALUE

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

cpu_count                            integer     60

parallel_threads_per_cpu                integer     2

resource_manager_cpu_allocation        integer     60

 

 

而操作系統上的邏輯cpu爲72，這裏是oracle使用cpu的個數，沒有全部分配給oracle使用,這裏有個疑問

[root@wtyzcdb23 ~]# grep processor /proc/cpuinfo | wc -l

72

 

數據庫使用的不是自動內存管理（AMM）

 

 

 

 

 

PGA內存自動管理

 

而根據之前的parallel_max_servers的設置方法計算：

Parallel_max_servers=2*60*5*4=2400

 

 

Bug 13743987 - A high CPU_COUNT can cause ORA-68 for parallel_max_servers (Doc ID 13743987.8)

 

 

 

目前parallel_max_servers參考統一支撐1庫，設置爲400

將_cursor_obsolete_threshold從1024調整爲200設置需要重啓生效