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What is an LSN: Log Sequence Number

LSNs, or Log Sequence Numbers, are explained on MSDN at Introduction to Log Sequence Numbers: Every record in the SQL Server transaction log is uniquely identified by a log sequence number (LSN). LSNs are ordered such that if LSN2 is greater than LSN1, Read More...
Posted 18 ianuarie 2012 05:33 from rusanu.com | (Comments Off)

SQL Server table columns under the hood

You probably can easily answer a question like ‘What columns does this table have?’. Whether you use the SSMS object explorer, or sp_help, or you query sys.column, the answer is fairly easy to find. But what is I ask ‘What are the physical Read More...
Posted 21 octombrie 2011 01:36 from rusanu.com | (Comments Off)

Understanding Hash, Sort and Exchange Spill events

Certain SQL Server query execution operations are calibrated to perform best by using a (somewhat) large amount of memory as intermediate storage. The Query Optimizer will choose a plan and estimate the cost based on these operators using this memory Read More...
Posted 19 octombrie 2011 22:28 from rusanu.com | (Comments Off)

T-SQL functions do no imply a certain order of execution

Looking at this question on StackOverflow: Conversion failed when converting from a character string to uniqueidentifier error in SQL Server one can see a reproducible example where a string split UDF works fine in the SELECT statement, but it gives a Read More...
Posted 10 august 2011 11:48 from rusanu.com | (Comments Off)
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Online Index Operations for indexes containing LOB columns

SQL Server supports online index and table rebuild operations which allow for maintenance operations to occur w/o significant downtime. While a table is being rebuild, or a new index is being built on it, the table is fully utilizable. It can be queried Read More...
Posted 6 august 2011 00:26 from rusanu.com | (Comments Off)

How to Multicast messages with SQL Server Service Broker

Starting with SQL Server 11 the the SEND verb has a new syntax and accepts multiple dialogs handles to send on: SEND ON CONVERSATION [(]conversation_handle [,.. @conversation_handle_n][)] [ MESSAGE TYPE message_type_name ] [ ( message_body_BLOCKED EXPRESSION Read More...
Posted 21 iulie 2011 04:40 from rusanu.com | (Comments Off)

How to update a table with a columnstore index

In my previous article How to use columnstore indexes in SQL Server we’ve seen how to create a columnstore index on a table and how certain queries can significantly reduce the IO needed and thus increase in performance by leveraging this new feature. Read More...
Posted 13 iulie 2011 11:01 from rusanu.com | (Comments Off)

How to use columnstore indexes in SQL Server

Column oriented storage is the data storage of choice for data warehouse and business analysis applications. Column oriented storage allows for a high data compression rate and as such it can increase processing speed primarily by reducing the IO needs. Read More...
Posted 13 iulie 2011 10:20 from rusanu.com | (Comments Off)

Download and Upload images from SQL Server via ASP.Net MVC

A frequent question that pops up on discussion forums is how to serve an image that is stored in a SQL Server table from an ASP.Net application. Unfortunately the answer is almost always wrong, as the prevalent solution involves copying the entire image Read More...
Posted 29 decembrie 2010 08:19 from rusanu.com | (Comments Off)

SqlDependency based caching of LINQ Queries

Query Notifications is the SQL Server feature that allows a client to subscribe to notifications that are sent when data in the database changes irrelevant of how that change occurs. I have talked before about how Query Notifications works in the article Read More...
Posted 4 august 2010 23:23 from rusanu.com | (Comments Off)

How to change database mirroring encryption with minimal downtime

SQL Server Database Mirroring uses an encrypted connection to ship the data between the principal and the mirror. By default RC4 encryption is enabled and used. The endpoint can be configured to use AES encryption instead, or no encryption. The overhead Read More...
Posted 23 aprilie 2010 22:33 from rusanu.com | (Comments Off)

Using tables as Queues

A very common question asked on all programming forums is how to implement queues based on database tables. This is not a trivial question actually. Implementing a queue backed by a table is notoriously difficult, error prone and susceptible to deadlocks. Read More...
Posted 26 martie 2010 21:02 from rusanu.com | (Comments Off)

Performance comparison of varchar(max) vs. varchar(N)

The question of comparing the MAX types (VARCHAR, NVARCHAR, VARBINARY) with their non-max counterparts is often asked, but the answer usually gravitate around the storage differences. But I’d like to address the point that these types have inherent, Read More...
Posted 23 martie 2010 06:03 from rusanu.com | (Comments Off)

Dealing with Large Queues

On a project I’m currently involved with we have to handle a constant influx of audit messages for processing. The messages come from about 50 SQL Express instances located in data centers around the globe, delivered via Service Broker into a processing Read More...
Posted 9 martie 2010 10:10 from rusanu.com | (Comments Off)

DbccCommand Enumeration

The SMO libraries contain an enum for the DBCC commands: DbccCommand. But there is little explanation in the MSDN documentation what those commands are. I had a recent discussion with a developer who, understandably, expected a little cleaner explanation Read More...
Posted 23 februarie 2010 08:36 from rusanu.com | (Comments Off)
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