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Slow I/O On HP Unix (Doc ID 457063.1)

Last updated on SEPTEMBER 29, 2017

Applies to:

Oracle Database - Enterprise Edition - Version 8.1.7.0 and later
HP OpenVMS VAX
HP-UX PA-RISC (64-bit)
HP-UX PA-RISC (32-bit)
HP OpenVMS Alpha
HP-UX Itanium
HP Tru64 UNIX

Symptoms

Disk utility output shows 100% usage for disk continously:

ProcList CPU Rpt Mem Rpt Disk Rpt NextKeys SlctProc Help Exit
 
       GlancePlus C.04.50.00     19:15:39 bplita3 ia64  Current Avg High 
------------------------------------------------------------------------ 
CPU  Util   S              SN NU U                       | 90%  90%  90% 
Disk Util   F                              F             |100% 100% 100%    <=== Disk Too heavily loaded



In Statspack or AWR report,  high 'free buffer waits' seen even after with considerably increasing db_cache_size and db writers.

Statspack Report Instance Efficiency Percentages (Target 100%) 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 
Buffer Nowait %:             99.99 Redo NoWait %:     99.99 
Buffer Hit %:                58.92 In-memory Sort %:  99.82 
Library Hit %:               89.19 Soft Parse %:      83.51 
Execute to Parse %:          50.76 Latch Hit %:      100.00 
Parse CPU to Parse Elapsd %: 81.48 % Non-Parse CPU:   93.21 
.... 

Top 5 Timed Events 
~~~~~~~~~~~~~~~~~~                            % Total 
Event                Waits        Time (s)    Ela Time 
-------------------- ------------ ----------- -------- 
free buffer waits          76,390      74,807    55.82 
enqueue                     4,071      11,625     8.67
.....

 

 

Cause

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In this Document
Symptoms
Cause
Solution
 1. Use the O/S striping software
 2. Use Direct IO
 mincache and convosync
 Parameters in Oracle influencing the use of Direct IO
 3. Concurrent I/O
 "-o cio"
References

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