Home » RDBMS Server » Performance Tuning » consistent gets > segment size during FTS (9.2.0.8 solaris 8)
consistent gets > segment size during FTS [message #281347] Fri, 16 November 2007 08:28 Go to next message
mlobel1
Messages: 2
Registered: November 2007
Junior Member
Hi everybody,

Why during a FTS the "consistent gets" are larger than the number of blocks in my table ? I will explain :

I created a table with 2 fields n number and c varchar2(50)
I inserted 58336 lines with n=1 and 32 lines with n=2
segment size is 512 blocks (blocksize is 8 kb)
I created a non unique index on n
My goal was testing execution plans issuing select *, select * where n=1 and select * where n=2 in these cases :
1- without any stats
2- with stats but no histograms
3- with stats and histograms

All the execution plans I obtained are the plans I expected.BUT :
I can not explain why tkprof ouputs 4392 consistent gets during a FTS issuing a select * from my_table knowing the segment size fot the table is 512 blocks.

Does anyone can explain me that behaviour ?

Thanks !
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Re: consistent gets > segment size during FTS [message #281351 is a reply to message #281347] Fri, 16 November 2007 08:36 Go to previous messageGo to next message
Michel Cadot
Messages: 64132
Registered: March 2007
Location: Nanterre, France, http://...
Senior Member
Account Moderator
Because you fetch many times to get the result.
Each time you fetch, you access the blocks (or associated undo blocks) that contains the data you fetch.

Regards
Michel
Re: consistent gets > segment size during FTS [message #281363 is a reply to message #281351] Fri, 16 November 2007 09:49 Go to previous message
mlobel1
Messages: 2
Registered: November 2007
Junior Member
So simple !
Thanks for your (very) quick answer.

Mathias
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