How to resolve Reporting Services Catalog Database File Existence Failed or Temporary Database File Existence failed

When you Uninstall SQl server some of the traces will be left behind one of them are Reporting serivces catalogs in order to fix this issue follow the screen shots below

Next to go to the Sql server root directory, by default

C:\Program Files\Microsoft SQL Server\MSSQL10_50.MSSQLSERVER\MSSQL\DATA

z

a

Files to be deleted

  • ReportServer.mdf
  • ReportServer_log.LDF
  • ReportServerTempDB.mdf
  • ReportServerTempDB_log.LDF.
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Implimenting Error Handling in SQL Server – Part 1

There are two types of Messages SQL Server returns

  1. Information Message
  2. Error Message

An informational Message as the name suggests SQL server sends the messages to the End user or client,

this can be anything including the output of DBCC commands or status of the server or it can also be a

output from the print command An Error message can be a warning message or error message from

SYS.MESSAGES catalog or from a RAISEEROR statement

As we go ahead we will be concentrating mostly on Error Messages in SQL server

There two types of Error Messages in SQL server

  1. System
  2. User Defined

if there is any exception during the execution,

The database engine picks up the information in the SYS.MESSAGES and sends it to the end user.

As there is need to customize the error messages so that errors are better understood at business

level these are called user defined error.

All the  System error messages and User defined error messages are stored in SYS.MESSAGES

SQL Server stores system and user-defined errors inside a catalog view called sys.messages.

This catalog contains all system error messages, which are available in many languages.

 

Each message has five properties arranged in columns:

■■ message_id:

This column stores the ID of a message and its value.  Together with language_id, this is unique across the instance. Messages with
IDs less than 50000 are system error messages.
■■ language_id:

This column indicates the language used in the message text, for example English or Spanish, as defined in the name column of the
sys.syslanguages system table. This is unique for a specified message_id.
■■ severity:

This column contains the severity level of the message. Whe you are creating errors, keep in mind that the severity must be the same for
all message languages within the same message_id.
■■ is_event_logged:

When you want to log the event when an error israised, set the value of this column equal to1. Like severity, this column must
be the same for all message languages within the same message_id.

■■ text: 

This column stores the text of the message. This text is written in the language indicated by the language_id property.

Severity Levels :  This indicates the severity of the error and this will help us the scope of the problem and how quick you need to respond

these levels are categorized into three main levels

  1.   Information Messages:  Level (0 to 10 )

Errors in this group are purely informational and are not severe. Status information or error reports are returned with a specific error code. SQL Server doesn’t use levels 1–9 these levels are available for user-defined errors.

2.     User Errors Level (11- 16)

These do not effect service or System or Server, most of these are corrected by the user and these are errors are raised when database Engine parses the query or Tsql statement for execution

3.  Software Errors (Levels 17–19):

Errors in this group are severe and require system administrator attention as well as yours. They are related to
problems in the Database Engine service and can’t be solved by users.

4.System Errors (Levels 20–25):

Errors in this group are critical since they indicate system problems. They are fatal errors that force the end of
the statement or batch in the Database Engine. Errors in this group record information about what occurred and then terminates. You must be aware that these errors can close the application connection to the instance of SQL Server. Error messages in this severity level group are written to the error log.

Mr  Pinal Dave had explained it in detail take a look at this post

http://blog.sqlauthority.com/2007/04/25/sql-server-error-messages-sysmessages-error-severity-level/

More detailed explanation from BOL

Severity Levels 0 through 19

Error messages with a severity level of 10 are informational. Error messages with severity levels from 11 through 16 are generated by user and can be corrected by the user. Severity levels from 17 and 18 are generated by resource or system errors; the user’s session is not interrupted.

Using sp_addmessage, user-defined messages with severities from 1 through 25 can be added to sysmessages. Only the system administrator can add messages with severities from 19 through 25.

Error messages with severity levels 17 and higher should be reported to the system administrator.

Severity Level 10: Status Information

Severity level 10 is an informational message and indicates a problem caused by mistakes in the information you have entered. Severity level 10 is not visible in SQL Server 7.0.

Severity Levels 11 through 16

These messages indicate errors that can be corrected by the user.

Severity Level 17: Insufficient Resources

These messages indicate that the statement caused SQL Server to run out of resources (such as locks or disk space for the database) or to exceed some limit set by the system administrator.

Severity Level 18: Nonfatal Internal Error Detected

These messages indicate that there is some type of internal software problem, but the statement finishes, and the connection to SQL Server is maintained. For example, a level 18 message occurs when the SQL Server query processor detects an internal error during query optimization.The system administrator should be informed every time a severity level 18 message occurs.

Severity Level 19: SQL Server Error in Resource

These messages indicate that some nonconfigurable internal limit has been exceeded and the current batch process is terminated. Level 19 errors occur rarely; however, they must be corrected by the system administrator or your primary support provider.The administrator should be informed every time a severity level 19 message occurs.

Severity Levels 20 through 25

Severity levels from 20 through 25 indicate system problems. These are fatal errors, which means that the process (the program code that accomplishes the task specified in your statement) is no longer running. The process freezes before it stops, records information about what occurred, and then terminates. The client connection to SQL Server closes, and depending on the problem, the client might not be able to reconnect.

Error messages with a severity level of 19 or higher stop the current batch. Errors messages with a severity level of 20 or higher are considered fatal errors and terminate the client connection. Errors messages in this range may affect all of the processes in the database, and may indicate that a database or object is damaged. Error messages with a severity level from 19 through 25 are written to the error log.

Severity Level 20: SQL Server Fatal Error in Current Process

These messages indicate that a statement has encountered a problem. Because the problem has affected only the current process, it is unlikely that the database itself has been damaged.

Severity Level 21: SQL Server Fatal Error in Database (dbid) Processes

These messages indicate that you have encountered a problem that affects all processes in the current database. However, it is unlikely that the database itself has been damaged.

Severity Level 22: SQL Server Fatal Error Table Integrity Suspect

These messages indicate that the table or index specified in the message has been damaged by a software or hardware problem.Level 22 errors occur rarely; however, if you should encounter one, run DBCC CHECKDB to determine if other objects in the database are also damaged. It is possible that the problem is in the cache only and not on the disk itself. If so, restarting SQL Server corrects the problem. To continue working, you must reconnect to SQL Server. Otherwise, use DBCC to repair the problem. In some cases, it may be necessary to restore the database.If restarting does not help, the problem is on the disk. Sometimes it can be solved by destroying the object specified in the error message. For example, if the message tells you that SQL Server has found a row with a length of 0 in a nonclustered index, delete the index and rebuild it.

Severity Level 23: SQL Server Fatal Error: Database Integrity Suspect

These messages indicate that the integrity of the entire database is suspect due to damage caused by a hardware or software problem.Level 23 errors occur rarely; however, if you should encounter one, run DBCC CHECKDB to determine the extent of the damage. It is possible that the problem is in the cache only and not on the disk itself. If so, restarting SQL Server corrects the problem. To continue working, you must reconnect to SQL Server. Otherwise, use DBCC to repair the problem. In some cases, it may be necessary to restore the database.

Severity Level 24: Hardware Error

These messages indicate some type of media failure. The system administrator might have to reload the database. It might also be necessary to call your hardware vendor.

How does the Buffer manager writes the data in the sql server

How does sql server writes the data , how does it enforces ACID property ,  why does  it use a LOG file ? what is write a head? What is a Dirty page ?

Are you looking answers for the above questions , then you don’t need to worry because you came to right place

 

Before answering the above questions , you need to know what is logical write and physical write

What is Logical write?

When the page is modified in the Buffer cache it is called a Logical write

What is Physical write?

When a page is written from a Buffer cache to a physical disk it is called a Physical write

 

How it works

when a user runs an update query after it is parsed successfully the query engine finds the efficient way to access the data by comparing the different execution plans, then these keys are passed to the  storage engine which finds the exact pages in the file and brings these pages into the buffer cache(Physical read) , once the pages are in the buffer cache , the data inside the page/s will be updated in the buffer cache(logical write), once these pages inside the buffer cache are updated the data is not directly written into the database file , first the updated pages are marked as dirty pages, a dirty page can under go any number of logical writes and for each logical write the logrecord is sent to the log cache as a log record , the log record is then inserted into the log file , after log record written into the disk(log file) the dirty page is then moved from buffer cache into the disk(data file) this is called flushing the page. SQL Server uses a technique known as write-ahead logging that prevents writing a dirty page before the associated log record is written to disk(data file)

 

When the buffer manager writes a page, it searches for adjacent dirty pages that can be included in a single gather-write operation. Adjacent pages have consecutive page IDs and are from the same file; the pages do not have to be contiguous in memory. The search continues both forward and backward until one of the following events occurs:

  • A clean page is found.
  • 32 pages have been found.
  • A dirty page is found whose log sequence number (LSN) has not yet been flushed in the log.
  • A page is found that cannot be immediately latched.

    In this way, the entire set of pages can be written to disk with a single gather-write operation.

 

Buffer management in SQL Server

 

Its very important to know how buffer manager works in the sql server to understand the query processing engine

Buffer management is a key component in achieving this efficiency. The buffer management component consists of two mechanisms:

  • The buffer manager to access and update database pages
  •  buffer cache (also called the buffer pool), to reduce database file I/O.

How Buffer management works in SQL server

  • Buffer cache is divided into  8 Kb pages
  • Buffer management performs two important functions
    • Reading data or index pages from the database disk files into the buffer cache
    • Writing modified pages back to disk
  • A page remains in the buffer cache until the buffer manager needs the buffer area to read in more data.
  •  Data is written back to disk only if it is modified. Data in the buffer cache can be modified multiple times before being written back to disk

    How is buffer cache is allocated:

When SQL Server starts, it computes the size of virtual address space for the buffer cache based on a number of parameters such as the amount of physical memory on the system, the configured number of maximum server threads, and various startup parameters

The two important counters for buffer management are BPOOL_COMMITTED & BPOOL_COMMIT_TARGET in the catalog view SYS.DM_OS_SYS_INFO

SQL Server reserves this computed amount of its process virtual address space (called the memory target) for the buffer cache, but it acquires (commits) only the required amount of physical memory for the current load

BPOOL_COMMITTED represents

Number of 8-KB buffers in the buffer pool. This amount represents committed physical memory in the buffer pool. Does not include reserved memory in the buffer pool.

BPOOL_COMMIT_TARGET (No pages SQL server acquired for buffer management but not commited) represents

Number of 8-KB buffers needed by the buffer pool. The target amount is calculated using a variety of inputs such as the current state of the system, including its load, the memory requested by current processes, the amount of memory installed on the computer, and configuration parameters. If the bpool_commit_target is larger than the bpool_committed value, the buffer pool will try to obtain additional memory. If the bpool_commit_target is smaller than the bpool_committed value, the buffer pool will shrink.

The time from sql server started and the buffer cache acquires memory target is called Ramp up

  •  single-page read request fills a single buffer page
  •  Ramp-up is expedited by transforming single-page read requests into aligned eight-page requests

Because the buffer manager uses most of the memory in the SQL Server process, it cooperates with the memory manager to allow other components to use its buffers. The buffer manager interacts primarily with the following components:

  • Resource manager to control overall memory usage and, in 32-bit platforms, to control address space usage.
  • Database manager and the SQL Server Operating System (SQLOS) for low-level file I/O operations.
  • Log manager for write-ahead logging.

Buffer manager features :

  • The buffer manager supports Hot Add Memory, which allows users to add physical memory without restarting the server.
  • The buffer manager supports large pages on 64-bit platforms. The page size is specific to the version of Windows
  • The buffer manager is non-uniform memory access (NUMA) aware

The buffer manager only performs reads and writes to the database. Other file and database operations such as open, close, extend, and shrink are performed by the database manager and file manager components.

Disk I/O operations by the buffer manager have the following characteristics:

  • All I/Os are performed asynchronously, which allows the calling thread to continue processing while the I/O operation takes place in the background.
  • All I/Os are issued in the calling threads unless the affinity I/O option is in use. The affinity I/O mask option binds SQL Server disk I/O to a specified subset of CPUs. In high-end SQL Server online transactional processing (OLTP) environments, this extension can enhance the performance of SQL Server threads issuing I/Os.
  • Multiple page I/Os are accomplished with scatter-gather I/O, which allows data to be transferred into or out of noncontiguous areas of memory. This means that SQL Server can quickly fill or flush the buffer cache while avoiding multiple physical I/O requests.

Long I/O Requests

The buffer manager reports on any I/O request that has been outstanding for at least 15 seconds. This helps the system administrator distinguish between SQL Server problems and I/O subsystem problems. Error message 833 is reported and appears in the SQL Server error log as follows:

SQL Server has encountered %d occurrence(s) of I/O requests taking longer than %d seconds to complete on file [%ls] in database [%ls] (%d). The OS file handle is 0x%p. The offset of the latest long I/O is: %#016I64x.

A long I/O may be either a read or a write; it is not currently indicated in the message. Long-I/O messages are warnings, not errors. They do not indicate problems with SQL Server. The messages are reported to help the system administrator find the cause of poor SQL Server response times more quickly, and to distinguish problems that are outside the control of SQL Server. As such, they do not require any action, but the system administrator should investigate why the I/O request took so long, and whether the time is justifiable.

Causes of Long-I/O Requests

A long-I/O message may indicate that an I/O is permanently blocked and will never complete (known as lost I/O), or merely that it just has not completed yet. It is not possible to tell from the message which scenario is the case, although a lost I/O will often lead to a latch time-out.

Long I/Os often indicate a SQL Server workload that is too intense for the disk subsystem. An inadequate disk subsystem may be indicated when:

  • Multiple long I/O messages appear in the error log during a heavy SQL Server workload.
  • Perfmon counters show long disk latencies, long disk queues, or no disk idle time.

Long I/Os may also be caused by a component in the I/O path (for example, a driver, controller, or firmware) continually postponing servicing an old I/O request in favor of servicing newer requests that are closer to the current position of the disk head. The common technique of processing requests in priority based upon which ones are closest to the current position of the read/write head is known as “elevator seeking.” This may be difficult to corroborate with the Windows System Monitor (PERFMON.EXE) tool because most I/Os are being serviced promptly. Long I/O requests can be aggravated by workloads that perform large amounts of sequential I/O, such as backup and restore, table scans, sorting, creating indexes, bulk loads, and zeroing out files.

Isolated long I/Os that do not appear related to any of the previous conditions may be caused by a hardware or driver problem. The system event log may contain a related event that helps to diagnose the problem.