Re: why ESTD_PHYSICAL_READS and ESTD_PHYSICAL_READ_TIME are not change in the same scale in v$db_cache_advice
- From: "qihua wu" <staywithpin@xxxxxxxxx>
- To: oracle-l <oracle-l@xxxxxxxxxxxxx>
- Date: Tue, 23 Oct 2007 08:41:22 +0800
Anybody can help me to understand this. Thanks for your help in advance
On 10/19/07, qihua wu <staywithpin@xxxxxxxxx> wrote:
>
> I have a system with much "db sequential read" so I want to increase the
> size of SGA, but when query v$db_cache_advice, I found that if I double the
> size of SGA, the ESTD_PHYSICAL_READ_TIME will be cut by 75%(from 199,882 to
> 48,111), but the ESTD_PHYSICAL_READS only be cut by less than 20% (from
> 747,430,817 to 563,865,027). So my question is why the read time reduced is
> not proportional to the physical read reduced.
>
> select c.SIZE_FACTOR, c.ESTD_PHYSICAL_READ_TIME,c.ESTD_PHYSICAL_READS,
> c.ESTD_PHYSICAL_READ_TIME/c.ESTD_PHYSICAL_READS from v$db_cache_advice c
>
> 0.0974 433635 956840262 0.000453194767425035
> 0.1949 365333 895650942 0.000407896628997237
> 0.2923 324082 858695632 0.000377411958233881
> 0.3897 296338 833841374 0.000355388937560683
> 0.4872 272305 812311393 0.000335222431134854
> 0.5846 238312 781858679 0.000304801886070769
> 0.6821 220777 766149079 0.000288164544018201
> 0.7795 212371 758619403 0.000279944065706951
> 0.8769 206007 752917466 0.000273611663034524
> 0.9744 201095 748517560 0.000268657691878331
> 1 199882 747430817 0.000267425419789722
> 1.0718 196718 744596185 0.000264194208838177
> 1.1692 192556 740867370 0.000259906169170333
> 1.2667 189031 737709474 0.000256240439715432
> 1.3641 185867 734874924 0.000252923312430239
> 1.4615 177746 727599826 0.000244290877551694
> 1.559 153407 705795703 0.000217353264334056
> 1.6564 100702 658579515 0.000152907883871851
> 1.7538 74071 634722204 0.000116698296566918
> 1.8513 48118 600045018 8.01906499622E-5
> 1.9487 48111 563865027 8.53236106093879E-5
>
>
>
>
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