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in v$sysstat
there are a parameter named "consistent changes"
the oracle explaination is:
Number of times a user process has applied rollback
entries to perform a consistent read on the block.
Work loads that produce a great deal of consistent changes
can consume a great deal of resources. The value of this
statistic should be small in relation to the "consistent gets"
statistic.
can somebody say more about that?
if this one is big, what should we do?
how and why this one go big?
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Hi,
You are right. That is number of times a user process gets the data from rollback segments. This number will increase depends on number of updations and deletions. You can't restrict this value. Because when you are updating or deleting a row, the corresponding before images will be placed in the rollback segments. Before the updation or deletion completes the commit or rollback If any other tx try to read the same page, then it reads the data from the rollback segements.
Even if u have enough space in buffer cache, it will do the same. this process doesn't effect the performance.
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