引數名	19c預設值	標準參考值	引數相關參考文件	COMMAND
_adg_parselock_timeout	0	ADG設定	使用新的隱含引數可以避免adg環境mrp程式crash之後資料庫關閉資料庫緩慢問題在下面的版本中fix Key PSUs/Bundles to target by version: - 11.2.0.x Apply the latest or terminal PSU/DBBP that the customer can access. - 12.1.0.2: 12.1.0.2.190416 or newer - 12.2.0.1: 12.2.0.1.DBRU:191015 or newer - 18.8.0.0: 18.8.0.0.DBRU:191015 or newer - 19.5.0.0 19.5.0.0.DBRU:191015 or newer	alter system set "_adg_parselock_timeout"=0 scope=spfile sid='*';
_ash_size	1048618	最小100M	增加_ash_size大小，避免alert日誌中頻繁出現ASH執行緊急重新整理及ASH緩衝溢位 Doc ID 1385872.1：Active Session History (ASH) Performed An Emergency Flush Messages In The Alert Log Doc ID 1403406.1:MMON Consuming a Huge Amount of Memory Raising ORA-4030 and Causing an Instance Hang Document 2268127.1 No Data in V$ACTIVE_SESSION_HISTORY When Size is _ASH_SIZE=1G Document 243132.1 Analysis of Active Session History (Ash) Online and Offline Document 1952274.1 MMNL Background Process Creates Large Trace Files Containing ASH Information 如果SGA足夠大，設定為250M	alter system set "_ash_size"=250M scope=spfile sid='*';
_clusterwide_global_transactions	TRUE	false	叢集範圍全域性事務是11g引入的特性，其容許XA事務在RAC中更加透明，當設定為FALSE時候，資料庫會將本地事務當作單獨的事務透過多階段提交協調處理，設定該引數不會有任何效能影響，可解決Bug 13605839 ORA-600 [ktbsdp1] ORA-600 [kghfrempty:ds] ORA-600 [kdBlkCheckError]. Corruption in Rollback with Clusterwide Global Transactions in RAC ORA-00600: [kjuscl:!free]	alter system set "_clusterwide_global_transactions"=FALSE scope=spfile sid='*';
_complex_view_merging	TRUE	TRUE	Bug 28959493 Wrong Result When Using Hash Join With Concatenated Columns Of Char	alter system set "_complex_view_merging"=TRUE scope=spfile sid='*';
_cursor_obsolete_threshold	8192	1024		alter system set "_cursor_obsolete_threshold"=1024 scope=spfile sid='*';
_datafile_write_errors_crash_instance	TRUE	FALSE	防止PDB中使用者datafile offline導致整個CDB crash，Multitenant best Practice and Known issues (Doc ID 1604135.1) Bug 13745317 - Datafile offline cause all instance down in a RAC env (Doc ID 13745317.8)	alter system set "_datafile_write_errors_crash_instance"=FALSE scope=spfile sid='*';
_gc_policy_minimum	15000	15000	There is no need to set _gc_policy_minimum if DRM is disabled by setting _gc_policy_time = 0. _gc_policy_minimum is a dynamic parameter, _gc_policy_time is a static parameter and rolling restart is not supported. To disable DRM, instead of _gc_policy_time, _lm_drm_disable should be used as it's dynamic. (Doc ID 1619155.1)	alter system set "_gc_policy_minimum"=15000 scope=spfile sid='*';
_log_segment_dump_parameter	TRUE	FALSE	控制log.xml切換時是否把非預設引數列印到alert中，建議設定成FALSE，12c Alert Log Appears To Show Unexpected Instance Restart (Doc ID 2049516.1) 可能會導致log file sync，浩成提供，徽商銀行	alter system set "_log_segment_dump_parameter"=FALSE scope=spfile sid='*';
_log_segment_dump_patch	TRUE	FALSE	控制log.xml切換時是否把補丁資訊列印到alert中，建議設定成FALSE，12c Alert Log Appears To Show Unexpected Instance Restart (Doc ID 2049516.1) 可能會導致log file sync，浩成提供，徽商銀行	alter system set "_log_segment_dump_patch"=FALSE scope=spfile sid='*';
_optimizer_adaptive_cursor_sharing	TRUE	FALSE	disabling extended cursor sharing and Adaptive Cursor Sharing,避免子游標過多，產生4031	alter system set "_optimizer_adaptive_cursor_sharing"=FALSE scope=spfile sid='*';
_optimizer_ads_use_result_cache	TRUE	FALSE	在 12C 上看到大量的'latch free'等待 (無論是從低版本升級上來的還是新安裝的) 當檢查 AWR 報告的時候，即使設定 RESULT_CACHE_MODE 為 MANUAL，在 latch statistics 部分顯示了對"Result Cache: RC Latch"的高競爭 see MOS 2002089.1,關閉自動動態統計資訊使用結果快取的機制	alter system set "_optimizer_ads_use_result_cache"=FALSE scope=spfile sid='*';
_optimizer_extended_cursor_sharing	UDO	none	disabling extended cursor sharing and Adaptive Cursor Sharing,避免子游標過多，產生4031	alter system set "_optimizer_extended_cursor_sharing"=none scope=spfile sid='*';
_optimizer_extended_cursor_sharing_rel	SIMPLE	none	disabling extended cursor sharing and Adaptive Cursor Sharing,避免子游標過多，產生4031	alter system set "_optimizer_extended_cursor_sharing_rel"=none scope=spfile sid='*';
_optimizer_gather_feedback	TRUE	false	disables the gathering of execution feedback in the optimizer	alter system set "_optimizer_gather_feedback"=FALSE scope=spfile sid='*';
_optimizer_use_feedback	TRUE	FALSE	11.2開始Oracle有了一種新的特性 Cardinality Feedback，Cardinality Feedback?是一個最佳化器自動最佳化的過程，最佳化器會自動修正重複執行的查詢的執行計劃。對於一些複雜的查詢，比如多欄位條件，字串範圍比較，資料SKEW?等等，以及缺乏統計資訊，最佳化器可能不能夠產生一個完全準確的基數估計,?如丟失或統計資料不準確，或複雜的謂詞的基數估計。?cardinality feedback?就是基於這一原因而產生的。 _optimizer_use_feedback?引數預設是TRUE，即開啟Cardinality Feedback，FALSE?為關閉Cardinality feedback。建議關閉?,目前Bug: Bug 8521689 - SubOptimal execution plan? on second execution of GROUP BY query? [ID 8521689.8]? Bug 20782505 : HIGH CPU USAGE VALIDATING? QUERY BLOCK HINTS? Bug 20370037 : KGLH0 GROWTH LEADING TO? ORA-4031? Bug 21571505 : REL11: ADAPTIVE PLAN? FEATURE POOR PERFORMANCE IN 12.1.0.2	alter system set "_optimizer_use_feedback"=FALSE scope=spfile sid='*';
_partition_large_extents	TRUE	FALSE	推薦值false，取消分割槽物件的8M區大小 11.2.0.2中引入了_PARTITION_LARGE_EXTENTS 的新特性，在EXTENT SIZE AUTO ALLOCATE的表空間上若建立分割槽表，則分割槽的INITIAL EXTENT SIZE為8M	alter system set "_partition_large_extents"=FALSE scope=spfile sid='*';

Oracle 19C 資料庫引數推薦（四）

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