1st execute SQL take much longer than 2nd execute

[markco]

If I have a SQL to retrive some data from DB and under the following condition, how can I check what should be the problem?
1) when the first time to run the SQL, it take about 30 sec to fatch all data back to the application. When the first run, the CPU loading is low but the disk IO is high.

2) After the first run, if I rerun the SQL again, it only take about 2 sec to fatch all data back. When the 2nd run, the CPU loading is high but the disk IO is low.

3) after the 2nd run, afterward execute the SQL, only take about 2 sec to fatch all data.

I had check the v$librarycache.gethitratio (SQL AREA) is about 0.998. Beside, what can I check? Markco Wong

 

[sem]

Your data is probably not in the buffer cache, so Oracle should read it from disk at first time.

select (1-(sum(decode(name,'physical reads',value,0))/
(sum(decode(name,'db block gets',value,0))+
sum(decode(name,'consistent gets',value,0)))))*100
"Hit Ratio" from v$sysstat