Why do queries run faster the second time?
When you run your query for the first time and the data is not in cache, the server read the data from disk. It is time-comsuming. The second time you execute the same query data is already in cache so it requires less time.
Why is my query suddenly slower than it was yesterday?
It is important to make sure that there are no maintenance tasks are running when queries are suddenly getting slower. I have often seen when backup jobs, statistics update or index maintenance tasks start they create resource crunch of IO, which leads to temporarily slow down of queries.
How can I speed up query execution?
Here are some key ways to improve SQL query speed and performance.
- Use column names instead of SELECT *
- Avoid Nested Queries & Views.
- Use IN predicate while querying Indexed columns.
- Do pre-staging.
- Use temp tables.
- Use CASE instead of UPDATE.
- Avoid using GUID.
- Avoid using OR in JOINS.
Why does the same query take different amount of time to run?
That can make a dramatic difference in performance if every read is coming from one of the caches rather than requiring a disk read. If you run the same query later after other work has flushed out most of the blocks your query is interested in, you may end up doing a ton of physical reads rather than being able to use the nicely warmed up cache.
Why do you get different query plans for different executions?
Are you getting different query plans for different executions (you may need to capture a query plan from your initial benchmarks and compare it to the current plan or you may need to increase your AWR retention to retain query plans for a few months in order to see this).
How long does it take to execute stored procedure?
Stored procedure works properly, but every time it takes different time to execute even if all parameters are the same. Execution time varies from 1 minutes to 8 minute. I am not able to find reason for this and i am not using any DBCC command in between.
How to force Oracle to use the same query plan?
Depending on the version of Oracle, there are various ways to force Oracle to use the same query plan. If you can drill down and figure out what the problem with statistics is, Oracle probably provides a way to give the optimizer better statistics.