SQL Server uses different types of locks at varying levels of granularity to control access to resources by transactions. Locking resources at a finer-grained level, like individual rows, increases concurrency but requires more locks. Locking at a coarser level, like entire tables, reduces the number of required locks but also decreases concurrency by restricting access to the entire resource. SQL Server automatically determines the appropriate lock level needed based on the transaction's data access needs.
SQL Server is able to service requests from a large number of concurrent users. When SQL Server is servicing requests from many clients, there is a strong possibility that conflicts will occur because different processes request access to the same resources at the same time. A conflict in which one process is waiting for another to release a resource is called a block. Although in SQL Server a blocked process usually resolves itself when the first process releases the resource but there are times when a process holds a transaction lock and doesn't release it. In this tip, we will learn different techniques to troubleshoot and resolve blocks in SQL Server.
SQL Server is able to service requests from a large number of concurrent users. When SQL Server is servicing requests from many clients, there is a strong possibility that conflicts will occur because different processes request access to the same resources at the same time. A conflict in which one process is waiting for another to release a resource is called a block. Although in SQL Server a blocked process usually resolves itself when the first process releases the resource but there are times when a process holds a transaction lock and doesn't release it. In this tip, we will learn different techniques to troubleshoot and resolve blocks in SQL Server.
Transactions and Concurrency Control in distributed systems. Transaction properties, classification, and transaction implementation. Flat, Nested, and Distributed transactions. Inconsistent Retrievals, Lost Update, Dirty Read, and Premature Writes Problem
DDBMS, characteristics, Centralized vs. Distributed Database, Homogeneous DDBMS, Heterogeneous DDBMS, Advantages, Disadvantages, What is parallel database, Data fragmentation, Replication, Distribution Transaction
This will tell about the three of the Protocols(Lock-Based Protocols, Timestamp-Based Protocols, Validation-Based Protocols) of Concurrency Control used in the database management system.
Uncovering SQL Server query problems with execution plans - Tony DavisRed Gate Software
Presentation by Tony Davis at SQL in The City 2016. An execution plan tells you exactly which tables and indexes SQL Server accessed, in what order, and what other operations it performed to return the data your query needed. But sometimes, the plan for even the simplest-looking query can reveal nasty surprises.
This session describes how SQL Server generates and reuses execution plans and the implications this has for you as the developer. After a quick-start guide to retrieving and reading plans, we'll focus on techniques that can help you track down high-cost queries quickly.
We'll cover tools such as ANTS Performance Profiler, as well as scripts that hunt down execution plans for queries that caused expensive scans, sort warnings, and other issues. Examining those plans, you'll uncover the root cause of the problem, often revealing issues such as inefficient indexing, data type mismatches, and misuse of functions.
Learn more about ANTS Performance Profiler: http://www.red-gate.com/products/dotnet-development/ants-performance-profiler/
Find out about all Redgate Products: http://www.red-gate.com/products/
Connect with Tony Davis on LinkedIn: https://www.linkedin.com/in/tony-davis-208b241
Transactions and Concurrency Control in distributed systems. Transaction properties, classification, and transaction implementation. Flat, Nested, and Distributed transactions. Inconsistent Retrievals, Lost Update, Dirty Read, and Premature Writes Problem
DDBMS, characteristics, Centralized vs. Distributed Database, Homogeneous DDBMS, Heterogeneous DDBMS, Advantages, Disadvantages, What is parallel database, Data fragmentation, Replication, Distribution Transaction
This will tell about the three of the Protocols(Lock-Based Protocols, Timestamp-Based Protocols, Validation-Based Protocols) of Concurrency Control used in the database management system.
Uncovering SQL Server query problems with execution plans - Tony DavisRed Gate Software
Presentation by Tony Davis at SQL in The City 2016. An execution plan tells you exactly which tables and indexes SQL Server accessed, in what order, and what other operations it performed to return the data your query needed. But sometimes, the plan for even the simplest-looking query can reveal nasty surprises.
This session describes how SQL Server generates and reuses execution plans and the implications this has for you as the developer. After a quick-start guide to retrieving and reading plans, we'll focus on techniques that can help you track down high-cost queries quickly.
We'll cover tools such as ANTS Performance Profiler, as well as scripts that hunt down execution plans for queries that caused expensive scans, sort warnings, and other issues. Examining those plans, you'll uncover the root cause of the problem, often revealing issues such as inefficient indexing, data type mismatches, and misuse of functions.
Learn more about ANTS Performance Profiler: http://www.red-gate.com/products/dotnet-development/ants-performance-profiler/
Find out about all Redgate Products: http://www.red-gate.com/products/
Connect with Tony Davis on LinkedIn: https://www.linkedin.com/in/tony-davis-208b241
Sql server performance tuning and optimizationManish Rawat
Sql server performance tuning and optimization
SQL Server Concepts/Structure
Performance Measuring & Troubleshooting Tools
Locking
Performance Problem : CPU
Performance Problem : Memory
Performance Problem : I/O
Performance Problem : Blocking
Query Tuning
Indexing
"Using Indexes in SQL Server 2008" by Alexander Korotkiy, part 1 Andriy Krayniy
Speakers Corner Event at Ciklum Dnepropetrovsk Office. Alexander Korotkiy, Senior .NET Developer talking Indexes in MS SQL Server.Speakers Corner Event at Ciklum Dnepropetrovsk Office. Alexander Korotkiy, Senior .NET Developer talking Indexes in MS SQL Server.
Understanding Locking Mechanisms in Database Systemskiansahafi
in this presentation i have tried to provide an in-depth explanation of the role of locking in SQL Server transactions.i have emphasized the importance of locking for maintaining transaction concurrency and data integrity in multi-user environments. The presentation covers the ACID test requirements, various lock modes (e.g., Exclusive, Shared, Update), and lock granularity. It also explains lock escalation and compares locking mechanisms in SQL Server, MySQL, and MongoDB. The presentation concludes by discussing the impact of locking mechanisms on data consistency and concurrency control, including the challenges of lock timeouts and deadlocks.
As CloudStack cannot work with any mysql clustering solution, it is time to explore a new locking service, manager and pluggable interface which would allow CloudStack DB to be HA enabled with multi-master read/write. Talk will focus on, - Need for a locking service and challenges with existing CloudStack architecture - Different possible clustering solution that can be adopted - Showcasing a PoC for future implementation with minimal changes to existing architecture using percona xtradb or any other clustering solution - Additionally, explore the idea of getting rid of mshost table, and use locking service to find about other management servers.
Compare the capabilities of the Microsoft Access, Microsoft SQL Serv.pdfarihantplastictanksh
Compare the capabilities of the Microsoft Access, Microsoft SQL Server, Oracle’s MySQL, and
Oracle relational database management systems (RDBMSs). Your paper should discuss the
processing speeds, data storage capabilities, maximum users supported, platforms supported,
user interfaces, development tools, vendor support, and cost. Discuss and cite at least two
references in addition to our textbook. Your paper should be 3-5 pages in length (excluding title
and References pages)
Solution
Microsoft Access
Overview:
Microsoft Access is a part of Microsoft Office,
it is commercially available database in the market
Inexpensive/standard on most computers
users can create complex databases
database professionalas can use construct a database
customers of MS-Access:
It is mainly used in small corporate companies or IT Sectors with 1-80 endusers.
Features of MS-Access:
1.It is having GUI Interface for creating databases
2. A databae contains tables, forms, reports, queries, macros.
3. It facilitates autocontent wizards to build tables or forms or reports.
4. It acts as an interface to other DBMS using ODBC
5. It is used for small business companies
6. Provides security like password protection
7. Provides a Data dictionary
8. We can repair the database
9. We can create different views
10. External data can be imported into Access
11. We can create web pages based using the database
12. It has as built in Macro functions
13. It uses Structurered Query Language
14. We can create forms, reports etc by using Visual Basic Application programming
15. Provides Add in controls like calendars
16. It can merged into word and analysed with Excel etc.
Issues:
Security:
User level security is very difficult
Tuning:
It does not have the ability to split over multiple Hard Drives, multiple CPUs or to place tables
into memory.
Locking:
Basic handling of concurrent users Backup and recovery at basic level.
ANSI SQL standard often doesn\'t work,MS-Access has it\'s own modified version of ANSI
SQL.
MySQL
Overview
MySQL is a database engine. It has a command line interface that allows the creation of
database. It Requires Front-end applications to access it for end users. EX:- C#, PHP, Microsoft
ASP.Net.
Typical users
Small companies or workgroups, through to very large Internet databases with large numbers of
users
Ex:wikipedia,Moodle.
Features
1. Speed:One of the fastest databases available
2. Ease of use: when compared to larger databases such as Oracle Uses standard SQL
3. Capability: A multi-threaded server allowing many clients to connect at the same time Fully
networked for the Internet with built in security
4.Portability: Runs on a many operating systems and different hardware
5. Small size: when compared to other large databases e.g. Oracle
6. Availabliity and Cost: Open Source ,Free in most situations to use
7. Open distribution and source code: You can check how it works – if you have the knowledge.
8. interface to other DBMS’s using Open Database Connectivit.
2. Microsoft® SQL Server™ has allows different types of
resources to be locked by a transaction. To minimize the cost of
locking, SQL Server locks resources automatically at a level
appropriate to the task. Locking at a smaller granularity, such
as rows, increases concurrency, but has a higher overhead
because more locks must be held if many rows are locked.
Locking at a larger granularity, such as tables, are expensive in
terms of concurrency because locking an entire table restricts
access to any part of the table by other transactions, but has a
lower overhead because fewer locks are being maintained.
INTRODUCTION
3. Locking is a major part of every RDBMS and is important
to know about. It is a database functionality which without
a multi-user environment could not work. The main
problem of locking is that in an essence it's a logical and
not physical problem. This means that no amount of
hardware will help you in the end. Yes you might cut
execution times but this is only a virtual fix. In a heavy
multi-user environment any logical problems will appear
sooner or later.
5. SQL Server can lock these resources
(listed in order of increasing granularity).
6. Shared locks (S)
Shared (S) locks allow concurrent
transactions to read (SELECT) a resource.
No other transactions can modify the data
while shared (S) locks exist on the
resource. Shared (S) locks on a resource
are released as soon as the data has been
read, unless the transaction isolation level
is set to repeatable read or higher, or a
locking hint is used to retain the shared (S)
locks for the duration of the transaction.
8. Update locks (U)
Update locks are a mix of shared and
exclusive locks. When a DML statement is
executed SQL Server has to find the data it
wants to modify first, so to avoid lock
conversion deadlocks an update lock is used.
Only one update lock can be held on the data
at one time, similar to an exclusive lock. But
the difference here is that the update lock itself
can't modify the underlying data. It has to be
converted to an exclusive lock before the
modification takes place. You can also force
an update lock with the UPDLOCK hint.
10. Exclusive locks (X)
Exclusive locks are used to lock data being
modified by one transaction thus
preventing modifications by other
concurrent transactions. You can read data
held by exclusive lock only by specifying a
NOLOCK hint or using a read uncommitted
isolation level. Because DML statements
first need to read the data they want to
modify you'll always find Exclusive locks
accompanied by shared locks on that same
data.
12. Intent locks (I)
Intent locks are a means in which a transaction
notifies other transaction that it is intending to lock
the data. Thus the name. Their purpose is to assure
proper data modification by preventing other
transactions to acquire a lock on the object higher in
lock hierarchy. What this means is that before you
obtain a lock on the page or the row level an intent
lock is set on the table. This prevents other
transactions from putting exclusive locks on the table
that would try to cancel the row/page lock. In the
example we can see the intent exclusive locks being
placed on the page and the table where the key is to
protect the data from being locked by other
transactions.
14. Schema locks (Sch)
There are two types of schema locks:
Schema stability lock (Sch-S): Used
while generating execution plans. These
locks don't block access to the object
data.
Schema modification lock (Sch-M):
Used while executing a DDL statement.
Blocks access to the object data since
its structure is being changed.
15. Example:
we can see the Sch-S and Sch-M locks being taken on the system tables and
the TestTable plus a lot of other locks on the system tables.
16. Bulk Update locks (BU)
Bulk Update locks are used by bulk
operations when TABLOCK hint is used
by the import. This allows for multiple
fast concurrent inserts by disallowing
data reading to other transactions.
17. Conclusion
Hopefully this PPT has shed some light on
how SQL Server operates with locks and
why is locking of such importance to proper
application and database design and
operation. Remember that locking
problems are of logical and not physical
nature so they have to be well thought out.
Locking goes hand in hand with transaction
isolation levels so be familiar with those
too. In the next article I'll show some ways
to resolve locking problems.