[THIN] Re: IT Could happen to you...SQL Database Corruption 101
- From: "David Teague" <DavidT@xxxxxxxxxxxxxxx>
- To: <thin@xxxxxxxxxxxxx>
- Date: Wed, 1 Sep 2004 09:23:50 -0400
Jim,
I know a lot about administrating sql servers, all this is great
advice, remember the transaction logs are the important part! When I
setup a database for a customer depending on their needs I will back up
the transaction logs at least every 4 hours, and the database once a
day, sometimes less. I do this for two reason, 1st, the backup of the
transaction log, also cleans out the log so you do not run out of space,
also if you have to do a restore from a previous nights backup you will
at least a have some recent restores of your transaction logs to get you
close to when the database failed, four our customer's the database's
change by the minutes so this is important. Depending on your webpage
database I would at least back up the transaction log daily. I have
attached a sql script that can get you out of a bind if your transaction
log gets full, so you do not have to restore from backup to resolve that
issue. This works for both sql 7 and 2000.
David Teague
Support Anaylst
TMTsoftware
919-493-4700
-----Original Message-----
From: Jim Kenzig http://thin.net [mailto:jimkenz@xxxxxxxxxxxxxx]
Sent: Wednesday, September 01, 2004 8:53 AM
To: thin@xxxxxxxxxxxxx; windows2000@xxxxxxxxxxxxx
Subject: [THIN] IT Could happen to you...SQL Database Corruption 101
Hi All,
As some of you may or may not of noticed my web site the Thin.net had
some
"issues" yesterday. Issues which led me down an all night path of why
you
need to regularly backup the transaction logs of your SQL 2000 database.
First off all disclaimers on the Thin.net apply. I am a NOVICE SQL
admin, I
have had to learn SQL because it is showing up everyplace. (Now even in
Citrix) You need to know some basic backup procedures to save your soul.
Perform these functions at your own risk. I take no liability about what
you
do to your system by using this information. OK Here goes:
Apparently there are two files critical for you database. One has a .mdf
extension and the other has a .ldf extension. The transaction logs as I
understand it reside in the .ldf portion of your Database
My web site is completely backended with SQL via the use of Cold Fusion.
There are about 4 different databases that control different things
there. I
regularly back up the databases to a file on my drive and then back up
the
back up file onto my DLT Tape drive. I have always been able to
restore my
databases from backup by performing the following procedure:
Expand the server that contains the "Database" directory that has your
databases that need restored.
1. Right click on "Databases" < Select "New" < Restore Database
2. Under the "General" Tab < Select the radio button for "From Device"
a) Add device
b) browse to directory - only one database should be added since the
application will create a .mdf and .ldf file (logs) for each database.
Adding in the names of ALL databases will result in ONE .mdf and .ldf
file
shared for all of them.
c) after database is added in, click OK
3. Back on "General" tab, make sure "Database Complete" is selected.
4. Also check that the database name you are restoring is accurate in
text
field (located at top of menu).
5. Go to "Option" menu. At botton of menu, select "Leave Database
Operational. Do not restore Transition log." if you aren't restoring
logs
and only database.
6. Click OK A progress bar should appear on the screen indicating the
restore is in progress. Repeat these steps for each database that needs
to
be restored.
Now if you had the smarts to take your database offline and backup its
.ldf
and .mdf files you could of simply taken the database offline and
swapped
out these files into your database directory with the
corrupted ones and put the database back online. Or you could right
click on
the server and attach the database by selecting these files.
But what happens when your backup .bak file is too old or is corrupted
and
either the .mdf file or the .ldf file is corrupted. You pretty much
end up
SOL if you haven't been backing up something
Anyways here is what happened to me and it could very easily happen to
you.
The .ldf file ran out of space on my Ads database for some reason. This
database also controls some other stuff on my site and
it virtually broke my site by being down. I knew it was out of space
because that is what the error message said. It even told me how I could
try
and fix it. The error read: Error: 9002, Severity: 17, State: 6
The log file for database 'aspads' is full. Back up the transaction log
for
the database to free up some log space. Ok so I learned that there is a
tick box when you back up the database to clear out free space in the
transaction log. So I tried to just back up the transaction log to clear
it
and that did not work.
We'll I thought I had a good .bak file yesterday but it turns out that
my
backup job wasn't set up exactly right. My fault. After a bunch of
different restore attempts, I ended up going back a year where I did
have a
good backup to restore what I could and then enter the rest (til 3 am
this
morning) to get the database up to date.
Lesson learned:
Make sure that: BACKUP FREQUENTLY!
1. Your database .mdf and .ldf files are set up with enough space to
grow on
your drive. You can take your database offline, right click on
properties
for it and make changes to these in the appropriate fields and put the
database back online.
2. Backup the .bak files from your backup often.
3. Take the database offline and make a backup copy of the .ldf and .mdf
files so that you can return to a point in time if all else fails.
4. Look carefully at your maintenance plan. SET ONE UP IF YOU DON'T HAVE
ONE! SQL Server has a great wizard that sets it up for you. Be certain
that
the Transaction log is getting backed up and cleared of extra space by
right
clicking on your maintenance plan in the MMC and choosing properties and
then clicking on the Transaction Log Backup tab and checking the box to
BACK
UP THE TRANSACTION LOG AS PART OF THE MAINTENCE PLAN. I don't think this
is
chosen by default so you need to do this after you set up your maintence
plan. There is a similar choice if you do a manual backup.
By backing up the transaction log it will free up some space in it so
that
it doesn't run out of space and crash your database. IT CAN and DID
happen
to me.
Do this and you will save yourself a lot of headaches in the future.
Trust
me.
My only savior was that I was able to restore my database from an older
.bak
file using the above procedure.
Hope this helps someone out there. If you have anything to add let me
know.
I'll post this as an article on Ondemandaccess.com once I have all ideas
and
feedback.
Regards,
Jim Kenzig
http://thin.net
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