【MOS】Top Ten Performance Mistakes Found in Oracle Systems. (文件 ID 858539.1)

lhrbest發表於2016-09-25

In this Document

Purpose
Troubleshooting Steps
References


APPLIES TO:

Oracle Database - Enterprise Edition - Version 9.2.0.8 and later
Information in this document applies to any platform.
RDBMS


PURPOSE

The purpose of this note is to inform reader about Top ten Performance mistakes  commonly found in Oracle Systems. This list is not in any particular order or priority.

TROUBLESHOOTING STEPS



Bad Connection Management 

The application connects and disconnects for each database interaction. This problem is common with stateless middleware in application servers. It has over two orders of magnitude impact on performance, and is totally unscalable. 

Bad Use of Cursors and the Shared Pool 

Not using cursors results in repeated parses. If bind variables are not used, then there is hard parsing of all SQL statements. This has an order of magnitude impact in performance, and it is totally unscalable. Use cursors with bind variables that open the cursor and execute it many times. Be suspicious of applications generating dynamic SQL. 

Bad SQL 

Bad SQL is SQL that uses more resources than appropriate for the application requirement. SQL that consumes significant system resources should be investigated for potential improvement. 

Use of Nonstandard Initialization Parameters 

These might have been implemented based on poor advice or incorrect assumptions. Most systems will give acceptable performance using only the set of basic parameters. In particular, parameters associated with _SPIN_COUNT on latches and undocumented optimizer features can cause a great deal of problems that can require considerable investigation. 

Likewise, optimizer parameters set in the initialization parameter file can override proven optimal execution plans. For these reasons, schemas, schema statistics, and optimizer settings should be managed together as a group to ensure consistency of performance. 


Getting Database I/O Wrong 

Many sites lay out their databases poorly over the available disks. Other sites specify the number of disks incorrectly, because they configure disks by disk space and not I/O bandwidth. 

Redo Log Setup Problems 

Many sites run with too few redo logs that are too small. Small redo logs cause system checkpoints to continuously put a high load on the buffer cache and I/O system. If there are too few redo logs, then the archive cannot keep up, and the database will wait for the archive process to catch up. 

Serialization of data blocks

Serialization of data blocks in the buffer cache due to lack of free lists, free list groups, transaction slots (INITRANS), or shortage of rollback segments. 

This is particularly common on INSERT-heavy applications, in applications that have raised the block size above 8K, or in applications with large numbers of active users and few rollback segments. Use automatic segment-space management (ASSM) to and automatic undo management solve this problem. 

Long Full Table Scans 

Long full table scans for high-volume or interactive online operations could indicate poor transaction design, missing indexes, or poor SQL optimization. Long table scans, by nature, are I/O intensive and unscalable. 

High Amounts of Recursive (SYS) SQL 

Large amounts of recursive SQL executed by SYS could indicate space management activities, such as extent allocations, taking place. This is unscalable and impacts user response time. Use locally managed tablespaces to reduce recursive SQL due to extent allocation. Recursive SQL executed under another user Id is probably SQL and PL/SQL, and this is not a problem. 

Deployment and Migration Errors 

In many cases, an application uses too many resources because the schema owning the tables has not been successfully migrated from the development environment or from an older implementation. Examples of this are missing indexes or incorrect statistics. These errors can lead to sub-optimal execution plans and poor interactive user performance. When migrating applications of known performance, export the schema statistics to maintain plan stability using the DBMS_STATS package. 

This note is from Oracle documentation:

Oracle? Database Performance Tuning Guide
10g Release 2 (10.2)

B14211-03

 

 

REFERENCES

NOTE:601807.1 - Oracle 11gR1 Upgrade Companion
NOTE:466181.1 - Oracle 10g Upgrade Companion
NOTE:215187.1 - All About the SQLT Diagnostic Tool
NOTE:223117.1 - Troubleshooting I/O Related Waits
NOTE:228913.1 - Systemwide Tuning using STATSPACK Reports
NOTE:402983.1 - * Master Note: Database Performance Overview
NOTE:94036.1 - Init.ora Parameter "CURSOR_SHARING" Reference Note
NOTE:396940.1 - Troubleshooting and Diagnosing ORA-4031 Error [Video]


About Me


..........................................................................................................................................................................................................................................................................................................

● 本文來自於MOS轉載文章,(文件 ID  858539.1)

● 本文在itpub(http://blog.itpub.net/26736162)、部落格園(http://www.cnblogs.com/lhrbest)和個人微信公眾號(xiaomaimiaolhr)上有同步更新

● QQ群:230161599  微信群:私聊

● 小麥苗分享的其它資料:http://blog.itpub.net/26736162/viewspace-1624453/

● 小麥苗雲盤地址http://blog.itpub.net/26736162/viewspace-1624453/

● QQ群: 230161599   微信群:私聊

● 聯絡我請加QQ好友(642808185),註明新增緣由

●【版權所有,文章允許轉載,但須以連結方式註明源地址,否則追究法律責任】

..........................................................................................................................................................................................................................................................................................................

手機長按下圖識別二維碼或微信客戶端掃描下邊的二維碼來關注小麥苗的微信公眾號:xiaomaimiaolhr,免費學習最實用的資料庫技術。



來自 “ ITPUB部落格 ” ,連結:http://blog.itpub.net/26736162/viewspace-2125539/,如需轉載,請註明出處,否則將追究法律責任。

相關文章