Performance Engineering Interview Question 6

Performance Engineering Interview Questions #6

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Following are the Performance Engineering Interview Questions Set #6.

Performance Engineering Interview Question 6

Q. 26 What does the low value of the soft parse ratio indicate?

Ans: Under ‘Instance Efficiency Percentages (Target 100%)’, check the value of Soft Parse % (or Soft Parse Ratio), if the value is low, then it indicates there could be a parsing issue. A lower ratio could also indicate that bind variables are not used or some other issue is causing SQL not to be reused.

Q. 27 What does the low value of the Liberary Hit % (ratio) indicate?

Ans: Under ‘Instance Efficiency Percentages (Target 100%)’, check the value of Library Hit % (or Library Hit Ratio), if the value is low, then it indicates that either the shared pool is too small or the system did not make correct use of bind variables in the application.

Q. 28 What is the ‘Execute to Parse’ ratio?

Ans. The ‘Execute to Parse’ ratio measures the ratio of the number of times a SQL is executed versus the number of times it is parsed.

The value of ‘Execute to Parse %’ should be very high in an ideal database. The ratio will be:

  1. Positive / High: If the number of executions of the SQL is more than the number of parses. This is a good case.
  2. Zero: If the number of executions of the SQL and parses are almost equal.
  3. Negative: If this value is negative, it means that the number of parses is larger than the number of executions. Another cause for a negative ‘Execute to Parse Ratio’ is if the shared pool is too small and queries are ageing out of the shared pool and need to be reparsed. This is another form of thrashing which also significantly degrades performance.

Q. 29 When does ‘Soft Parse’ occur?

Ans: A soft parse occurs when a session attempts to execute a SQL statement and a usable version of the statement is already in the shared pool.

Q. 30 When does ‘Hard Parse’ occur?

Ans: A hard parse occurs when the current SQL statement is either not in the shared pool or not there in a shareable form.

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