I'm trying to understand value you find in v$sysstat for "physical reads", "db block gets", and "consistent gets".
My book says this:
Consistent Gets. Number of blocks accessed in the buffer cache for queries without the Select For Update clause.
DB Block Gets. Number of blocks in the buffer cache that were accessed for INSERT, UPDATE, DELETE, and SELECT For UPDATE.
Physical Reads. Number of blocks that were read from disks to satisfy a SELECT, SELECT For UPDATE, INSERT, UPDATE, or DELETE.
I did a basic test on a database with a table that has 20+ million records. I restarted the database to flush out buffer cache.
Then I simply did a select * from bigtable.
I then queried the v$sysstat table for the value of "physical reads", "db block gets", and "consistent gets". What I saw, as the query was running and returning results, was that the consistent gets value kept rising much, much faster than physical reads.
By the time the query was done running, Consistent Gets rose 64,627 and Physical Reads only 1,775.
Keep in mind, my session was the only one connected to the database.
Does this make sense to anyone??
I would have expected Physical Reads to go through the roof, especially with the database just being started.
Why didn't I see this??
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