1.what is the diff between nolock optimizer and read uncommitted isolation?

1.what is the diff between nolock optimizer and read
uncommitted
isolation?
2.what is the diff between revoke and deny?
3.what is percieved down time?
4.whether password protection are required for backups?if
yes why?if no why?
5.what is fill factor?
6.what is cost analysis?
7.what is mean by piece meal restore?
8.what is 'rowguidcol'?
9.impersonate permission?
10.what is selectivity?

Question Posted / durga prasad

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1.what is the diff between nolock optimizer and read uncommitted isolation? 2.what is the diff..

Answer / Ziaul Qamar

1. Nolock optimizer and Read Uncommitted are both techniques used in SQL Server to read data quickly, but they do so with different levels of consistency. Nolock hint is a query hint that tells SQL Server to bypass some locking mechanisms during execution, while Read Uncommitted isolation level allows dirty reads, non-repeatable reads, and phantom reads.
2. Revoke and Deny are both SQL commands used to manage database permissions, but they have different effects. Revoke removes an existing permission for a user or role, while Deny overrides any existing permission by explicitly denying access.
3. Perceived Down Time (PDT) is the amount of time users experience when a system is unavailable or performing poorly, even if the actual downtime is shorter due to maintenance or other reasons.
4. Yes, password protection is required for backups because backups may contain sensitive data and should be secure from unauthorized access. Password protection ensures that only authorized individuals can restore the backup.
5. Fill Factor is a percentage value used in SQL Server to control how much space is left empty between data pages during index creation or rebuild operations, improving performance by reducing fragmentation.
6. Cost Analysis is a process used in database management systems to estimate the resources required for executing a query or operation, based on factors like the number of rows affected and the complexity of the query.
7. Piece Meal Restore refers to restoring only specific parts of a backup instead of the entire backup set. This can save time and resources, especially when dealing with large backups.
8. 'rowguidcol' is a special column in SQL Server used for generating unique row identifiers, typically in merge replication scenarios where rows may be updated or inserted on different servers.
9. Impersonate Permission allows a user to execute queries and other actions as another user, which can be useful for troubleshooting or debugging purposes. n10. Selectivity refers to the proportion of matching rows returned by a query, with highly selective queries returning fewer rows (e.g., WHERE clause filters) and less selective queries returning more rows (e.g., wildcard searches).

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