What does the percentage scanned from cache in the Query Profile signify? A. The percentage of data scanned from the local disk cache. B. The percentage of data scanned from the remote disk cache. C. The percentage of data scanned from the metadata cache. D. The percentage of data scanned from the query cache.
Answer (1)
The percentage scanned from cache in the context of a Query Profile typically signifies how much of the data, required to execute a query, was retrieved from a cache rather than being accessed directly from the main database or storage system. Cache memory can significantly speed up query performance by storing frequently accessed data.
In the context of the multiple-choice question, the correct option is C. The percentage of data scanned from the metadata cache.
Here's a breakdown of the concept:
What is Cache? Cache is a smaller, faster storage that stores copies of frequently accessed data. It helps reduce access times to data stored in slower main storage systems.
What is a Query Profile? A Query Profile provides insights into how a database query is executed, including how various resources are utilized. It's typically used by database administrators to optimize query performance.
Types of Caches in Computing:
Local Disk Cache: Temporarily stores data on a local disk to speed up read access.
Remote Disk Cache: Stores data from remote sources to improve access times.
Metadata Cache: Stores metadata, which is data about data, to improve query performance.
Query Cache: Saves the result set of a query so that the exact same query doesn't have to be re-executed.
Why is Metadata Cache Relevant Here? Metadata cache is used to store metadata, such as database object definitions, schema, and other data descriptors. By retrieving metadata from the cache rather than regenerating it, the efficiency of query execution is improved.
In summary, understanding which cache is being referenced in the percentage scanned can help database administrators and users optimize their data query processes and resources. It signifies efficiencies in how data retrieval is being managed.
