Tài liệu MASTERING SQL SERVER 2000- P12 ppt

This page intentionally left blank Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. Administering SQL Server PART IV LEARN TO: • Perform basic administrative tasks • Automate administration • Provide security in SQL Server 2000 2627ch16.qxt 8/22/00 10:58 AM Page 571 Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. This page intentionally left blank Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. CHAPTER 16 Basic Administrative Tasks FEATURING: Backing Up Your Data 574 Restoring Databases 596 Devising a Backup Strategy 604 Maintaining Indexes 608 Reading the Logs 613 Copying Databases 614 Summary 620 2627ch16.qxt 8/22/00 10:58 AM Page 573 Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. I f you were to buy a brand-new car, how long do you think it would continue to run without any maintenance? It may last a few months, maybe even a year, before it finally breaks down and quits functioning altogether. If you want to keep your car running in top shape for years to come, you have to perform regu- lar maintenance, such as changing the oil, rotating the tires, etc. SQL Server is no dif- ferent; you must perform regular maintenance if you want to keep your server in top running condition. The first maintenance task we will explore is probably the most important: You must perform regular backups. Without a backup strategy, you can—no, you will—lose data. Therefore you will want to pay close attention as we discuss each of the four types of backup (full, differential, transaction log, and filegroup) and how to use each one. Another important topic that we will cover is how to read the SQL Server error logs and what to do with the information you find there. SQL Server keeps its own error logs apart from the Windows NT logs that you may be used to reading in Event Viewer, so this section of the book will serve you well. Finally we will delve into the depths of index maintenance. We created indexes in Chapter 12; now we need to know how to keep them running by performing regular maintenance on them. We’ll start by looking into backups. Backing Up Your Data A backup is a copy of your data that is stored somewhere other than the hard drive of your computer, usually on some type of tape (a lot like the kind you listen to), but a backup can also be stored on a hard drive on another computer connected over a local area network. Why would you want to keep a copy of your data in two places? There are many reasons. The first reason for keeping a backup is hardware failure. Computer hardware has a Mean Time Between Failures (MTBF) that is measured in hours. This means that every 4000 hours or so, a piece of hardware is going to fail, and there is little you can do about it. True, you could implement fault tolerance by providing duplicate hardware, but that is not a complete guarantee against data loss. So if you don’t want to lose your data when a hard disk goes bad, it is best to back up. Another reason that comes to mind is natural disaster. No matter how much redundant hardware you have in place, it is not likely to survive the wrath of a tor- nado, hurricane, earthquake, flood, or fire. To thwart the wrath of the elements, you need to back up your data. A final reason is provoked by all of the injustice we see in today’s world. Many employees are angry with their boss or the company in general, and the only way 2627ch16.qxt 8/22/00 10:58 AM Page 574 Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. 575 they see to get revenge is by destroying or maliciously updating sensitive data. This is the worst kind of data loss, and the only way to recover from it is by having a viable backup. Now that you have some very good reasons to back up your data, you need to know how to do it. We’ll look into four different types of backup that you can per- form to protect your data, but first you need to know how the backup process works. How Backups Work Some things are common to all types of backup. For instance, you may be wondering when you are going to be able to get your users off the database long enough to per- form a backup. Stop wondering—all backups in SQL Server are online backups, which means that your users can access the database while you are backing it up. How is this possible? Transaction logs make this possible. In Chapter 3, you learned that SQL Server issues checkpoints on databases to copy committed transactions from the transaction log to the database. The transaction log is a lot like a diary; in a diary, you put a date next to everything that happens to you. It might look as follows: 12-21-99 Bought a car 12-22-99 Drove new car to show off 12-23-99 Drove car into tree 12-24-99 Started looking for new car Much like a diary, a transaction log also puts a log sequence number (LSN) next to each line of the log. A transaction log would look as follows: 147 Begin Tran 1 148 Update Tran 1 149 Begin Tran 2 150 Update Tran 2 151 Commit Tran 1 152 Checkpoint 153 Update Tran 2 154 Commit Tran 2 When a backup is started, SQL Server records the current LSN. Then, once the backup is complete, SQL Server backs up all of the entries in the transaction log from the LSN it recorded at the start of the backup to the current LSN. Here’s an example of BACKING UP YOUR DATA Administering SQL Server PART IV 2627ch16.qxt 8/22/00 10:58 AM Page 575 Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. CHAPTER 16 • BASIC ADMINISTRATIVE TASKS 576 how it works: First SQL Server checkpoints the data and records the LSN of the oldest open transaction (in this case, 149 Begin Tran 2, because it was not committed before the checkpoint). Next, SQL Server backs up all of the pages of the database that actu- ally contain data (no need to back up the empty ones). Finally, SQL Server grabs all of the parts of the transaction log that were recorded during the backup process—that is, all of the lines of the transaction log with an LSN higher than the LSN recorded at the start of the backup session (in this case, 149 and above). In this way your users can still do whatever they want with the database while it is being backed up. To perform any type of backup, though, you need a place to store it. The medium that you will use to store a backup is called a backup device. Let’s see how to create them now. Creating a Backup Device Backups are stored on a physical backup media, which can be a tape drive or a hard disk (local or over a network connection). SQL Server is not aware of the various forms of media attached to your server, so you must inform SQL Server where to store the backups. That is what a backup device is for; it is a representation of the backup media. There are two types of backup devices to create: permanent and temporary. Temporary backup devices are created on the fly, when you perform the actual backup. They are very useful for making a copy of a database to send to another office so that they can have a complete copy of your data. Or you may want to consider using a temporary backup device to make a copy of your database for permanent off- site storage (usually for archiving). NOTE Although it is true that you could use replication (discussed in Chapter 27) to copy a database to a remote site, backing up to a temporary backup device may be faster if your remote site is connected via a slow WAN link (such as 56K frame relay). Permanent backup devices can be used over and over again, and you can even append data to them, making them the perfect device for regularly scheduled backups. Permanent backup devices are created before the backup is performed and, like tempo- rary devices, can be created on a local hard disk, on a remote hard disk over a local area network, or on a local tape drive. Let’s create a permanent backup device now: 1. Open Enterprise Manager by selecting it from the SQL Server 2000 group under Programs on the Start menu and expand your server, then Management. 2. Click Backup in the contents pane. 2627ch16.qxt 8/22/00 10:58 AM Page 576 Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. 577 3. On the Action menu, select New Backup Device. 4. In the Name box of the Backup Device Properties dialog box, enter NwindFull. Notice that the filename and path are filled in for you; make sure you have enough free space on the drive that SQL Server has selected. 5. Click OK to create the device. If you go to Windows Explorer and search for a file named NwindFull.bak right now, don’t be too surprised if you don’t find one. SQL Server hasn’t created a file just yet; it simply added a record to the sysdevices table in the master database telling SQL Server where to create the backup file the first time you perform a backup to the device. So don’t worry, it will be there as soon as you perform a backup. In fact, let’s work with full backups right now. TIP If you are using a tape drive as a backup medium, it must be physically attached to the SQL Server machine. The only way around this is to use a third-party backup solution. Performing a Full Backup Just as the name implies, a full backup is a backup of the entire database. It backs up the database files, the locations of those files, and portions of the transaction log (from the LSN recorded at the start of the backup to the LSN at the end of the backup). This is the first type of backup you need to perform in any backup strategy because all of the other backup types depend on the existence of a full backup. This means that you cannot perform a differential or transaction log backup if you have BACKING UP YOUR DATA Administering SQL Server PART IV 2627ch16.qxt 8/22/00 10:58 AM Page 577 Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. CHAPTER 16 • BASIC ADMINISTRATIVE TASKS 578 never performed a full backup. To create your baseline (which is what the full backup is called in a backup strategy), let’s back up the Northwind database to the permanent backup device you created in the last section of this chapter: 1. Open Enterprise Manager and expand your server, then databases. 2. Right-click Northwind and select Properties. 3. On the Options tab, clear the Select Into/Bulk Copy and Truncate Log on Checkpoint boxes so you can perform a transaction log backup later. 4. Click OK to apply the changes. 5. Select Northwind under Databases and on the Action menu, point to All Tasks and select Backup Database. 6. In the Backup dialog box, make sure Northwind is the selected database to back up and the name is Northwind Backup. 7. In the Description box, type Full Backup of Northwind. 8. Under Backup, select Database – Complete (this is the full backup). 9. Under Destination, click Add. 2627ch16.qxt 8/22/00 10:58 AM Page 578 Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. 579 10. In the Select Backup Destination box, click Backup Device, select NwindFull, and click OK. 11. In the Backup dialog box, under Overwrite, select Overwrite Existing Media. This will initialize a brand-new device or overwrite an existing one. 12. On the Options tab, select Verify Backup upon Completion; this will check the actual database against the backup copy to see whether they match after the backup is complete. BACKING UP YOUR DATA Administering SQL Server PART IV 2627ch16.qxt 8/22/00 10:58 AM Page 579 Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark. [...]... it to another location Finally, before SQL Server will allow you to restore a database, SQL Server performs a safety check to make sure you are not accidentally restoring the wrong database The first thing SQL Server does is compare the database name that is being restored with the name of the database recorded in the backup device If the two are different, SQL Server will not perform the restore This... let’s make one of the databases suspect so that you can see exactly what SQL Server does to restore it Specifically, let’s blow away Northwind: 1 Open the SQL Server Service Manager from the Start menu 2 Select the MSSQLServer service and click the Stop button (the red square) 3 You will be asked whether you wish to stop the MSSQLServer service and then whether you wish to stop all dependent services... 4 Find the filename northwnd.mdf (usually in C:\program files\microsoft sql server\ mssql\data\) 5 Rename the file northwnd.old 6 Find the file named northwnd.ldf and rename it northwndlog.old 7 From the Service Manager, restart the SQLServerAgent and MSSQLServer services 8 Open Enterprise Manager and expand databases under your server name Northwind should be gray and marked Suspect Please purchase... when restoring the differential backup, SQL Server will not allow you to restore any other backups; you have told SQL Server in effect that you are done restoring, so let everyone start using the database again If you have more than one file to restore, you need to specify NORECOVERY on all restores except the last one Another feature to point out is that SQL Server remembers where the original files... remove this watermark 597 PA R T IV Administering SQL Server 2627ch16.qxt 2627ch16.qxt 598 8/22/00 10:58 AM Page 598 CHAPTER 16 • BASIC ADMINISTRATIVE TASKS NOTE You needed to stop all of the SQL Server services because while they are running, all of the databases are considered open files, and you would not be able to work with them outside of SQL Server Now that you have a suspect database on your... partial restores work: 1 Open Query Analyzer by selecting it from the SQL Server 2000 group under Programs on the Start menu 2 Enter and execute the following code to restore the sales database to a new database named sales_part: RESTORE DATABASE sales_part1 FILEGROUP = ‘secondary’ FROM DISK=’F:\Program Files\Microsoft SQL Server\ MSSQL\BACKUP\NwindFull.BAK’ WITH FILE=6,RECOVERY,PARTIAL, MOVE ‘sales_data’... This means that if you backed up files from the D drive, SQL Server will restore them to the D drive This is great unless your D drive has completely failed and you need to move your database to the E drive You will also run into this problem if you have backed up a database on a server at the home office and need to restore the database to a server at a child office In this instance, you need to use... the last transaction log backup It is easier to understand the role of the transaction log backup if you think of the transaction log the way SQL Server does, as a separate object If you think of the transaction log as a separate object, it makes sense that SQL Server would require a backup of the database as well as the log Besides the fact that a transaction log is an entity unto itself, there is another... and select Restore Database 3 Notice here that SQL Server remembers where you backed everything up Make sure that all of the backups are checked 4 On the Options tab, select Leave Database Operational Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark 8/22/00 10:58 AM Page 599 RESTORING DATABASES 599 PA R T IV Administering SQL Server 2627ch16.qxt 5 Click OK to perform the... performed, but it is still a great deal smaller than the full backup, which makes a differential faster than a full backup SQL Server figures out which pages in the backup have changed by reading the last LSN of the last full backup and comparing it with the data pages in the database If SQL Server finds any updated data pages, it will back up the entire extent (eight contiguous pages) of data, rather than . over a network connection). SQL Server is not aware of the various forms of media attached to your server, so you must inform SQL Server where to store the. that we will cover is how to read the SQL Server error logs and what to do with the information you find there. SQL Server keeps its own error logs apart