Database Cache Hit ratio is very less

Question

Hi All,
my live database Cache Hit ratio is very less. can some one proposed relevant solution for that.
SELECT (1-((phy.value-phyd.value) / (cur.value + con.value))) * 100 "Cache Hit ratio"
FROM v$sysstat cur, v$sysstat con, v$sysstat phy, v$sysstat phyd
WHERE cur.name = 'db block gets'
AND con.name = 'consistent gets'
AND phy.name = 'physical reads'
AND phyd.name = 'physical reads direct';
Cache Hit ratio
47.99717699362490769958384625413175240442
select NAME,VALUE from v$parameter where name like '%db_cache_size%';
NAME VALUE
db_cache_size 335544320
select name, value From v$sysstat
where name in ('db block gets', 'consistent gets', 'physical reads');
NAME VALUE
db block gets 30047032214
consistent gets 691770165681
physical reads 376120181932
Thanks

Answer 1

user1093072 wrote:
Hi all thanks a lot for your answers. i am getting some query time outs and while investigating got less ratios. can some one tell me how to get dicission using this ratios
Buffer Hit % 95.71
Cache Hit ratio 47.99The fact that you get two different values for "the same thing" is a clue that (a) your SQL statement is suspect and (b) your logic is flawed.
You SQL is going to give you some kind of (meaningless) average since the database started up. The report you showed looks like part of an AWR or statspack report which will be covering a short interval of time. The difference between the two percentages may mean the two approaches are using different formula, or it may mean that the result is highly dependent on the time window.
Since you have access to AWR/statspack - run off a report for a (short) interval when the system is performing well, and for when the system is performing badly, and compare them.
As a starting point you could post the two sections "Load Profile" and "Top 5 Timed Events" to the forum for initial comment. If you do so, please make sure you use the "code" tags (see end of post) to make the output readable or you may get no replies.
Regards
Jonathan Lewis
http://jonathanlewis.wordpress.com
http://www.jlcomp.demon.co.uk
To post code, statspack/AWR report, execution plans or trace files, start and end the section with the tag {noformat}{noformat} (lowercase, curly brackets, no spaces) so that the text appears in fixed format.
There is a +"Preview"+ tab at the top of the text entry panel. Use this to check what your message will look like before you post the message. If it looks a complete mess you're unlikely to get a response. (Click on the +"Plain text"+ tab if you want to edit the text to tidy it up.)