SQLSERVER Interview Questions-part2
- What's
the maximum size of a row?
8060 bytes.
- What
is lock escalation?
Strong names are required to store
shared assemblies in the global assembly cache (GAC). This is because the
GAC allows multiple versions of the same assembly to reside on your system
simultaneously, so that each application can find and use its own version
of your assembly. This helps avoid DLL Hell, where applications that may
be compiled to different versions of your assembly could potentially break
because they are all forced to use the same version of your assembly.
Another reason to use strong names is to make it difficult for hackers to
spoof your assembly, in other words, replace or inject your assembly with
a virus or malicious code.
- What's
the difference between DELETE TABLE and TRUNCATE TABLE commands?
DELETE TABLE is a logged operation, so
the deletion of each row gets logged in the transaction log, which makes
it slow. TRUNCATE TABLE also deletes all the rows in a table, but it won't
log the deletion of each row, instead it logs the deallocation of the data
pages of the table, which makes it faster. Of course, TRUNCATE TABLE can
be rolled back.
- What
are constraints? Explain different types of constraints.
Constraints enable the RDBMS enforce
the integrity of the database automatically, without needing you to create
triggers, rule or defaults. Types of constraints: NOT NULL, CHECK, UNIQUE,
PRIMARY KEY, FOREIGN KEY
- What
is an index?
Indexes in SQL Server are similar to
the indexes in books. They help SQL Server retrieve the data quicker.
- What
are the types of indexes?
Indexes are of two types. Clustered
indexes and non-clustered indexes. When you craete a clustered index on a
table, all the rows in the table are stored in the order of the clustered
index key. So, there can be only one clustered index per table.
Non-clustered indexes have their own storage separate from the table data
storage. Non-clustered indexes are stored as B-tree structures (so do
clustered indexes), with the leaf level nodes having the index key and
it's row locater. The row located could be the RID or the Clustered index
key, depending up on the absence or presence of clustered index on the
table.
- I
create a separate index on each column of a table. what are the advantages
and disadvantages of this approach?
If you create an index on each column
of a table, it improves the query performance, as the query optimizer can
choose from all the existing indexes to come up with an efficient
execution plan. At the same t ime, data modification operations (such as
INSERT, UPDATE, DELETE) will become slow, as every time data changes in
the table, all the indexes need to be updated. Another disadvantage is
that, indexes need disk space, the more indexes you have, more disk space
is used.
- What
is RAID and what are different types of RAID configurations?
RAID stands for Redundant Array of
Inexpensive Disks, used to provide fault tolerance to database servers.
There are six RAID levels 0 through 5 offering different levels of
performance, fault tolerance.
- What
are the steps you will take, if you are tasked with securing an SQL
Server?
Preferring NT authentication, using
server, databse and application roles to control access to the data,
securing the physical database files using NTFS permissions, using an
unguessable SA password, restricting physical access to the SQL Server,
renaming the Administrator account on the SQL Server computer, disabling
the Guest account, enabling auditing, using multiprotocol encryption,
setting up SSL, setting up firewalls, isolating SQL Server from the web
server etc.
- What
is a deadlock and what is a live lock? How will you go about resolving
deadlocks?
Deadlock is a situation when two
processes, each having a lock on one piece of data, attempt to acquire a
lock on the other's piece. Each process would wait indefinitely for the
other to release the lock, unless one of the user processes is terminated.
SQL Server detects deadlocks and terminates one user's process. A livelock
is one, where a request for an exclusive lock is repeatedly denied because
a series of overlapping shared locks keeps interfering. SQL Server detects
the situation after four denials and refuses further shared locks. A
livelock also occurs when read transactions monopolize a table or page, forcing
a write transaction to wait indefinitely.
