EM408 Backup and Recovery of SQL Anywhere Tips and Techniques

EM408Backup and Recovery of SQL AnywhereTips and Techniques • Reg Domaratzki • Sustaining Engineering • iAnywhere Solutions • Reg.Domaratzki@sybase.com

Points of Persistent Data Automatic Recovery Backing Up Your Database Backup Considerations in a Replicating Environment Recovery from Media Failure Backup Strategies EM408 - Backup and Recovery of SQL Anywhere : Tips & Techniques

Unlike some DBMS systems, ASA relies on the operating system to manage the files associated with maintaining data Main Database File DBSpaces Transaction Log Mirror Transaction Log All of these files are read and written to disk based on the page size specified on the dbinit command line Points of Persistent Data

The name of the main database file is specified on the dbinit command line It may or may not contain the full path to the database file The main database file generally contains all the table pages and index pages associated with the database Main Database File

A DBSpace is another database file that also keeps table pages and index pages There are two main reasons that DBspaces are used Performance - Putting index pages and table pages on separate devices can often speed up transactions that require index balancing 2GB File Limit - On FAT file systems, ASA will only support a file up to 2GB in size The path name specified for the location of the DBSpace must be consistent if you move the database to another machine DBSpaces

The transaction log is stored in a separate file and is also specified on the dbinit command line All changes to the database are stored in the transaction log in the order that they occur The transaction log should reside on a different device than the database file By default, the transaction log is put on the same device and in the same directory as the database—this does not protect against media failure The Transaction Log

An identical copy of the transaction log Maintained at the same time as the transaction log Every time a database change is written to the transaction log, it is also written to the transaction log mirror file By default, a mirrored transaction log is not used Using a Transaction Log Mirror

Media failure on the device where the transaction log resides can result in you losing your current transaction log Because changes are written to the transaction log before they are written to the main database file, you can lose your most recent data if your transaction log is lost By mirroring your transaction log to a different device, you protect your most recent data in the case of media failure Because there is no strong I/O to network devices, we cannot guarantee recoverability of the database if a transaction log resides on a network device Why Use a Transaction Log Mirror?

The server checks that the transaction log and its mirror are identical by carrying out a full comparison of the two files on startup If the server finds that the transaction log and the mirror are identical up to the end of the shorter of the two files, the remainder of the longer file is copied into the shorter file If the check finds that the log and the mirror are different in the body of the shorter of the two, one of the two files is corrupt and the engine will shut down Validating the Transaction Log on Database Startup

Points of Persistent Data Automatic Recovery Backing Up Your Database Backup Considerations in a Replicating Environment Recovery from Media Failure Backup Strategies Where are we?

In order to ensure database recovery in the case of a system failure, ASA keeps two other logs internally in addition to the transaction log The Checkpoint Log The Rollback Log Automatic Recovery

A checkpoint is an event that causes all dirty pages in memory to be written to disk A database file is composed of pages Before a page is updated (made dirty), a copy of the original is always made The copied pages are place in the checkpoint log Following a checkpoint, the checkpoint log is deleted The checkpoint log is physically located within the main database file The checkpoint log

Also stored in the main database file There is a separate rollback log for each connection Every time a transaction is started, the rollback log will contain the SQL statements needed to undo the transaction in case a ROLLBACK command is executed The rollback log for a given connection is deleted once a COMMIT or ROLLBACK is executed The rollback log

Adaptive Server Anywhere automatically takes three steps to recover from a system failure: Restore all pages to the most recent checkpoint, using the checkpoint log Apply any changes made between the checkpoint and the system failure. These changes are in the transaction log Roll back all uncommitted transactions, using the rollback logs Step 3 may take a long time if there are long uncommitted transactions that have already done a great deal of work since the last checkpoint Steps to recover from a system failure

Backup Terminology Validating your Database Full Backups Incremental Backups Backing up your Database

Full backup Makes a copy of the database file and (optionally) a copy of the transaction log Incremental backup Makes a copy of only the transaction log Online backups Backups can be made without stopping the server Offline backups Database files are copied while the database server is not running Backup Terminology

Client-side Backup An external process connects to the database engine and copies the files to an alternate location Server-side Backups The database engine itself copies the files to an alternate location Image Backups Copies the database and/or transaction log to another directory Archive Backups Creates a single file holding all required backup information Can be a single file or a tape drive device name Backup Terminology

Before doing a full backup, it is a good idea to verify that the database file is not corrupt using dbvalid By default, all dbvalid does is to scan all the rows in all the tables and ensure that an index entry exists for each row You can increase the amount of work done by dbvalid by adding additional options WITH INDEX CHECK (-fi) will make sure that each entry in every index has a corresponding row in the table WITH DATA CHECK (-fd) will make sure that data in a row that may spill onto additional pages actually exists WITH FULL CHECK (-f) does an index check and a data check Check the validity of the database

Instead of backing up the database file and transaction log to another directory, all database files can be backed up into a single file that can be written directly to tape Only one file can be stored on each tape Meant for backing up very large databases Archive Backups

An offline backup can be made without using ASA by physically copying the database and log file to an alternate location You can also do a client-side full backup using the dbbackup command line utility and specifying the database file name in the connection parameters It is significantly faster to use the operating system to copy the files if you are performing an offline backup Performing an offline full backup

A client-side online full backup can be made using the dbbackup command line utility and specifying the server name and database name in the connection parameters dbbackup –c “eng=asa8;dbn=db1;uid=dba;pwd=sql” c:\backup A server-side online full backup can be performed using the BACKUP command when connected to the database BACKUP DATABASE TO ‘c:\backup’; Note that the directory ‘c:\backup’ in a client-side backup is relative to where dbbackup is run from, and in a server-side backup, the directory is relative to the database engine Performing an online full backup

If the database is not running, you can simply copy the transaction log to your alternate location You can also do a client-side incremental backup using the dbbackup command line utility and specifying the database file name in the connection parameters Again, it is faster to use the operating system copy commands to perform an offline backup Performing an offline incremental backup

A client-side online incremental backup can be made using the dbbackup command line utility dbbackup –t –c “eng=asa8;dbn=db1;uid=dba;pwd=sql” c:\backup A server-side online incremental backup can be performed using the BACKUP command BACKUP DATABASE TO ‘c:\backup’ TRANSACTION LOG ONLY; Performing an online incremental backup

Using operating system commands If the database engine was shut down cleanly, and the database engine isn’t running, you can delete or rename the current transaction log and transaction log mirror with no side effects The next time the database engine starts, since no log file currently exists, and new log file will be created with a starting log offset that matches with the end of the recently deleted/renamed log file Managing the transaction log

Using client-side backups -t : Only back up the transaction log -r : Rename and restart the current transaction log The current transaction log (after being backed up) is renamed to a file based on the current date and a new empty current log file is created -x : Delete and restart the current transaction log The current transaction log (after being backed up) is deleted and a new empty current log file is created -xo : Delete and restart the current transaction log without backup The current log file is simply deleted This limits your recoverability options -n : rename local backup of transaction log to match server When backing up the log file to the backup directory, use a file name that matches the renamed log file of the current transaction log This ensures that log files in your backup directory are not overwritten Managing the transaction log

Using server-side backups TRANSACTION LOG ONLY Equivalent to the –t switch on dbbackup TRANSACTION LOG RENAME Equivalent to the –r switch on dbbackup TRANSACTION LOG RENAME MATCH Equivalent to using the –r –n switches on dbbackup TRANSACTION LOG TRUNCATE Equivalent to the –x switch on dbbackup Managing the transaction log

There are two reasons why dbbackup may wait for all transactions to finish The current transaction log is being renamed A transaction cannot span to separate log files, so all transactions must be committed or rolled back for a log file rename to occur. The WAIT BEFORE START clause is used on server-side backups Using this clause ensures that there is nothing in the database file that will cause automatic recovery to occur when the database is started next Specifically, all the rollback logs must be empty, meaning that there are no active transactions) When does dbbackup wait for all transactions to finish?

Do not run dbvalid on a database file that you have just backed up unless you can guarantee that the database engine will not need to go through recovery on startup The WAIT BEFORE START option was used You did an offline backup During recovery, the engine will roll back transactions that were not committed, and will make changes to the database and log file This will prevent this database from being used in certain recovery situations (more on this later) If you have used the WAIT BEFORE START or done an offline backup, then you can start the database engine in read-only mode and run dbvalid Running dbvalid on backed up database files

If you back up on top of the previous backup, and you get a media failure in the middle of the backup, you are left with no backup at all You should also keep some of your full backups offsite to protect against fire, flood, earthquake, theft, or vandalism Keep several full backups

A live backup is an extra precaution you can take to protect your current log file A client-side connection is made using dbbackup -l dbbackup first takes a full copy of the current transaction log dbbackup will stay connected to the database engine and every time a new page is written to the current transaction log, the engine will also send a copy of this page to dbbackup Therefore, a duplicate copy of the current transaction log can be maintained on a separate machine Live Backups

In v7, you can now use event scheduling to automatically back up your database The next few slides show an implementation of a backup strategy Database file resides at c:\em408.db Transaction log resides at d:\em408.log Local backup directory is f:\ Network mapped drive “\\backup\loc” is an offsite machine used for backup redundancy A full backup is taken each Sunday Before the full backup, all the current files are archived so we don’t overwrite what might be the only good backup An incremental backup is taken each night 8 A.M. on Sunday and 3 A.M. each night were chosen to minimize the chances that there are open transactions at the time Scheduling Backups to Run

create event FullBackup schedule start time ‘9:00AM’ on (‘Sun’) handler begin backup database directory ‘f:\\' wait before start; xp_cmdshell(‘xcopy f:\*.* \\backup\loc /D /Q /Y’); end Scheduling a Full Backup

create event IncrementalBackup schedule start time ‘3:00AM' every 24 hours handler begin backup database directory ‘f:\\' transaction log only transaction log rename match; xp_cmdshell(‘xcopy f:\*.* \\backup\loc /D /Q /Y’); end Scheduling an Incremental Backup

create event CleanUp schedule start time ‘8:00AM’ on (‘Sun’) handler begin xp_cmdshell(‘del /Q /F f:\zip\backup.zip’); xp_cmdshell(‘pkzip -a f:\zip\backup.zip f:\*.*); xp_cmdshell(‘del /Q /F f:\*.*’); xp_cmdshell(‘del /Q /F \\backup\loc’); xp_cmdshell(‘copy f:\zip\backup.zip \\backup\loc’); end Scheduling Clean Up

Points of Persistent Data Automatic Recovery Backing Up Your Database Backup Considerations in a Replicating Environment Recovery from Media Failure Backup Strategies Overview

There are a few other things to consider in a replicating environment Protecting the current log files on the consolidated database Backing up old log files Backing up the messaging system dbremote -u Backup Considerations in a replicating environment

When dbremote runs, it will always scan the current transaction log If your current log file is lost, and dbremote has sent messages from a missing log file, you will have to re-extract all remote users that picked up the messages generated from the now missing log file It is extra important to make sure that there is a mirror log file on a separate device from that where the database file and log file reside This will protect you from media failure on a single device Protecting the Current Log File

In order to manage your log files, you will often rename and re-start your transaction logs Until every remote user has confirmed every transaction in a log file, you cannot delete the old logs, and dbremote will need to know where these old log files are located It is a good idea to backup these old log files to alternate media in case of media failure Keeping old log files should be considered completely separate from your backup and recovery procedures Just the old renamed log files cannot guarantee recoverability unless a valid backup strategy is also in place Backing up Old Log Files

There is no need to back up the messaging system The guaranteed delivery system that is implemented by dbremote will guarantee that any messages lost as a result of system failure or media failure will be resent Backing up the messaging system

Running dbremote with the -u option will force dbremote into only sending transactions that occur in the off-line logs Therefore, if the current transaction log (and mirror log) are both lost, you can guarantee that no remote users have received messages from the lost log and nobody will need to be re-extracted This will slow down the speed with which your remote sites receive data from he consolidated, but will guarantee that remotes need not be re-extracted should the current log be lost DBREMOTE -u

For the preceding section, the following naming conventions will be used The database file resides at c:\em408.db The transaction log resides at d:\em408.log The mirror transaction log resides at e:\em408.mlg The backup directory is located at f:\ A temporary recovery directory will be located at f:\recover ALL these directories are local to the machine Recovery naming conventions

Recovery from media failure requires you to keep the transaction log on a separate device from the database file Recovery depends on whether the media failure is on the device holding your database file or on the device holding your transaction log The first step in recovering from a media failure is to clean up, reformat, or replace the device that failed There are some special considerations if you are recovering a consolidated database Recovery from media failure

If your transaction log is still usable, but you have lost your database file, the recovery process depends on the number incremental backups you have taken since your last full backup Media failure on the database file

If you have not deleted or restarted the transaction log since the last full backup, the current transaction log contains everything since the last backup Move the current logs to the recovery directory MOVE d:\em408.log f:\recover MOVE e:\em408.mlg f:\recover Restore the most recent full backup to the production directories COPY f:\em408.db c:\ /Y COPY f:\em408.log d:\ /Y COPY f:\em408.log e:\em408.mlg /Y Apply the TWO transaction logs to the backed up database DBENG7 c:\em408.db –a d:\em408.log DBENG7 c:\em408.db –a f:\recover\em408.log If you have a single transaction log

DBENG7 c:\em408.db –a f:\recover\em408.log Cannot open transaction log file – Can’t use log file “f:\recover\em408.log” since the offsets don’t match the offsets in the database file This error is a result of having started the backed up version of the database and having automatic recovery occur on the backed up database prior to having tried to apply subsequent log files Failure to apply the current transaction log

If you have run incremental backups since the last full backup, each transaction log since the full backup needs to be applied in sequence to bring the database up to date Move the current logs to the recovery directory Restore the most recent full backup to the production directories Apply all the transaction logs to the backed up database in the order with which they were backed up DBENG7 c:\em408.db –a d:\em408.log DBENG7 c:\em408.db –a f:\01081100.log DBENG7 c:\em408.db –a f:\01081101.log DBENG7 c:\em408.db –a f:\01081200.log DBENG7 c:\em408.db –a f:\recover\em408.log If you have multiple transaction logs

If your database file is still usable but you have lost your current or mirror transaction log Copy the good transaction log to the location of the lost transaction log COPY e:\em408.mlg d:\em408.log If you have lost BOTH the current and mirror transaction logs Make a backup of the database file immediately COPY c:\em408.db f:\recover Erase the current transaction logs if they still exist DEL d:\em408.log e:\em408.mlg Restart the database with the -f switch DBENG7 –f c:\em408.db The server will restore the database to the most recent checkpoint and then roll back any transactions that were not committed at the time of the checkpoint Media failure on the transaction log

NEVER NEVER NEVER NEVER NEVER use the -f recovery switch on a replicating database WARNING!!!!

EM408 Backup and Recovery of SQL Anywhere Tips and Techniques