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Block Reads...
- Thread starter hilbertl3
- Start date
jimbopalmer
Programmer
Carp is right, but here is some opinion that is not always right, but works for me.
A process with very high physical block reads is very often doing full table scans, (not using any index) Oracle tries not to keep entire table in memory at the expense of more frequently reused indexes. High physical block reads may be a sign you need an index.
A process with very high logical block reads is may be using a bad index, it takes examining a lot of index leaves to decide which row of the table to fetch. You may need a better index or you may need to give a hint to the optimizer.
Logical block reads are often 30,000 times as fast as a physical block read, (dirty reads, done dirt cheap) so if you have to trade off, take a larger hit in Logical block reads.
I tried to remain child-like, all I acheived was childish.
A process with very high physical block reads is very often doing full table scans, (not using any index) Oracle tries not to keep entire table in memory at the expense of more frequently reused indexes. High physical block reads may be a sign you need an index.
A process with very high logical block reads is may be using a bad index, it takes examining a lot of index leaves to decide which row of the table to fetch. You may need a better index or you may need to give a hint to the optimizer.
Logical block reads are often 30,000 times as fast as a physical block read, (dirty reads, done dirt cheap) so if you have to trade off, take a larger hit in Logical block reads.
I tried to remain child-like, all I acheived was childish.
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