|
One type of database corruption that is reported to Technical Support is typically associated with Assertion Error 50213, "Page number on page does not match page requested". When running on an ASA 6 or 7, the assertion will likely be 200601, "Page for requested record not a table page or record not present on page." Most frequently, however, said database was created on version 5.x and became corrupted before upgrading the software. Occasionally other assertions are reported, depending on the operation that first fails.
Our Product Quality department has stated that they would prefer to receive all databases in-house that become corrupted on version of the software that is currently being developed (as of this writing, SSA 5.5.05, ASA 6.0.4, ASA 7.0.1) in order to investigate the causes and frequency of database corruption. In some cases, however, the procedure described below can be more expedient. Furthermore, if the you are running on software that is no longer being updated (typically the maintenance level currently being sold plus one level earlier), the usefulness of such information is limited.
In all cases of database corruption, the preferred resolution is to find a valid backup, and apply all of the log files since the time of the backup.
This type of corruption is particularly bothersome, however, because it only manifests itself when a particular database page is accessed. If the data on that page is rarely used, the corruption may well exist on many or all of the backups the customer has on hand.
It may be possible to recover the database with the following procedure, although it is likely that some data will be lost. It is up to the customer to determine the validity and completeness of the data in the recovered database.
You will want to use the dbunload command; therefore it is prudent to note the following dbunload switches:
(at the command prompt type: dbunload /? )
Usage: dbunload [switches] <directory> [table-name-list]
Switches (use specified lower-case letter, as shown):
Adaptive Server Anywhere 6 and 7 include additional switches, notably -an and -ac, which can be used to roll the entire recovery process into a single command line. However, when using these switches, if the reload fails, the whole recovery process needs to be started from scratch. For this reason, we will use a manual, three-step process that leaves data and command files even in the event of a partial failure.
Create a working directory (eg c:\working) and an unload directory (eg c:\unload). Placing these directories off the root will save wear and tear on the fingers. Copy the database and log files to the working directory. Open a command prompt in the working directory. Run the following command line. (In this example we are using the asademo.db which comes with ASA6)
dbunload -c "uid=dba;pwd=sql;dbf=c:\working\asademo.db" -u c:\unload
The output will resemble:
Unloading "DBA"."sales_order" into c:\unload\192.dat (relative to server)
Unloading "DBA"."sales_order_items" into c:\unload\193.dat (relative to server)
Unloading "DBA"."contact" into c:\unload\194.dat (relative to server)
Unloading "DBA"."customer" into c:\unload\195.dat (relative to server)
Unloading "DBA"."fin_code" into c:\unload\196.dat (relative to server)
Unloading "DBA"."fin_data" into c:\unload\197.dat (relative to server)
Unloading "DBA"."product" into c:\unload\198.dat (relative to server)
Unloading "DBA"."department" into c:\unload\199.dat (relative to server)
Unloading "DBA"."employee" into c:\unload\200.dat (relative to server)
In a technical support case, we would see an assertion error message in the above example at this point. Assume table "customer" gave an Assertion Error.
Type the following:
dbunload -c "uid=dba;pwd=sql;dbf=c:\working\asademo.db" -u c:\unload -e dba.customer
The output will resemble:
Unloading "DBA"."sales_order" into c:\unload\192.dat (relative to server)
Unloading "DBA"."sales_order_items" into c:\unload\193.dat (relative to server)
Unloading "DBA"."contact" into c:\unload\194.dat (relative to server)
Unloading "DBA"."fin_code" into c:\unload\196.dat (relative to server)
Unloading "DBA"."fin_data" into c:\unload\197.dat (relative to server)
Unloading "DBA"."product" into c:\unload\198.dat (relative to server)
Unloading "DBA"."department" into c:\unload\199.dat (relative to server)
Unloading "DBA"."employee" into c:\unload\200.dat (relative to server)
This will either complete successfully or yield another corrupt table. Rerun the process with a comma-separated list of tables to exclude until the unload completes successfully.
We will now have a series of *.DAT files with the data we need, and a file called reload.sql with the schema for the database, except for the corrupt tables. We need a complete schema for the database. Type the following in order to create RELOAD1.SQL:
dbunload" -c "uid=dba;pwd=sql;dbf=c:\working\as[1] [2] 下一页 | 
