ISBN13 to ISBN10 Converter for SQL Server

October 24, 2014 | Blog Technical Solutions

ISBN13 -> ISBN10

Here’s a handy function for converting a 13-digit ISBN to its 10-digit equivalent in SQL Server T-SQL.

CREATE FUNCTION TO_ISBN10 ( @isbn varchar(13) )
    DECLARE @isbn10 varchar(10);
    DECLARE @forwards int;
    DECLARE @backwards int;
    DECLARE @check int;
    DECLARE @thisval int;

    SET @isbn10 =substring(@isbn,4,9);
    SET @forwards = 1;
    SET @backwards = 10;
    SET @check = 0;

    WHILE @forwards <= 9
        SET @thisval =cast(substring(@isbn10, @forwards, 1) AS INT)* @backwards;
        SET @check = @check + @thisval;
        SET @forwards = @forwards + 1;
        SET @backwards = @backwards - 1;

    SET @check = 11 -(@check % 11);

    IF @check = 10 begin
        SET @isbn10 = @isbn10 +'X';
        SET @isbn10 = @isbn10 +cast(@check AS VARCHAR(1));

    RETURN @isbn10;

Listing Outlook mailbox rules for all users

June 25, 2014 | Technical Solutions

Does your company use Outlook email forwarding? As your organisation has grown, have the rules become hard to manage?

We have a customer using Exchange Server for a few dozen users. They use mailbox rules so they can delegate various activities when staff are out of the office. Occasionally they lose track of what’s being forwarded, and it’s a pain to get this information from each user one by one. Here’s a little PowerShell script I threw together to automate it. I ran this on their server from the “Exchange Management Shell”. It’s my first PowerShell script ever; I’m used to Linux shell scripts and up till now haven’t made complex scripts under Windows. That may change:

PowerShell Script to list Outlook mailbox rules for users in an organisation

$users = get-mailbox

ForEach ($user in $users)
        $rules = get-InboxRule -Mailbox $
        if ($rules.length -gt 0) {
                echo ""
                echo $
                echo ""
                $rules | select name, priority, description | fl
                echo ""

Save this in a file with the extension “ps1” (that’s a one on the end) and run it from PowerShell to get the output – use > to redirect to a file if necessary. If you put the script in the current directory, you may need to explicitly specify the path, for example: .\run.ps1 > rules.txt Note that this only shows the server-side rules, such as placing messages in a folder, forwarding, etc. Anything that interacts with the client machine such as a popup will not appear in this report – this suits our customer because they want the rules to work when a user is not even logged in. The customer is pleased they can see the server-side rules in one report, and I’ve learned that it’s not just Linux that can support powerful scripting!

Backups affecting system performance – our LVM2 solution

April 4, 2014 | Technical Solutions


Our customer had a vendor product which used a MySQL database.  The nightly backup of the database was preventing users from accessing the data for the duration of the backup.  As the data grew, the backup was taking longer and longer, and this was causing problems with other system activity – timeouts and failures had become an issue.

There are various approaches to backing up MySQL which we don’t cover here.  In this case, it was not feasible to change the customer’s backup procedure at the time, so this workaround, which took just a couple of hours to implement and test, helped them avoid regular downtime for a few months until an alternative backup approach could be rolled out.

We reduced downtime from over an hour to a few seconds

Before we addressed the problem, our customer’s data would be inaccessible for at least one hour each night.  After we implemented our solution, the downtime was reduced to a few seconds.

If you are interested in reading the technical details of this solution, we share them below.  If you’d prefer to speak to us about a similar problem in your organisation, please fill in the contact form on the right and we will get in touch.


Ewan’s Technical Notes

A redeployment of the vendor software was already on the horizon, including database replication as the vendor’s preferred backup strategy. In the meantime, what was the most cost effective way to prevent the old backup from disabling the system?

LVM2 – Logical Volume Management

I had previously used LVM2 snapshots to perform low level file system backups on a running system. The commands are well documented elsewhere, so a summary should suffice: If a file system (volume) has been created in a volume group with enough free space left over, an instantaneous snapshot can be taken and maintained by LVM2, using copy-on-write.  My previous use of LVM2 was to create such snapshots and run “dump” on those to perform a backup, in the knowledge that if I’d got my sums right, the snapshot would remain valid long enough to complete the backup, without interrupting any continued attempts to change the real file system.

Of course, database backups should not normally be a simple backup of the file system. Even if a snapshot is taken to guarantee no changes to the data being backed up during the process, a restore does involve an element of recovery – to the database, it looks like the system was shut down uncleanly. How could the instant snapshot to be used to take a conventional database backup?

The solution was simple, and had been hinted at elsewhere in my Google searches: mount the LVM2 snapshot as a normal file system, and create a second MySQL configuration to allow it to be accessed, albeit through a non-standard MySQL port. Then a backup could be done by pointing “mysqldump” to this copy. After the backup, the second MySQL would be shut down, the file system unmounted and the snapshot deleted.

Digram of how we used LVM Snapshots to backup MySQL

Using LVM Snapshots to backup MySQL

So that the second MySQL would not “wake up” to a file system requiring recovery, there was the need to lock the tables just like the previous “mysqldump” would do – but only for long enough to create the LVM2 snapshot, which is just a few seconds. Reducing the system pause to such a short time meant there were no longer any timeouts or failures.

This change to the backups was quick to implement and bought us time to properly roll out new deployments of the vendor software with an entirely different mechanism for backups. Having previously enjoyed using LVM2 for more conventional uses, this was an interesting and novel use which gave us a few months to breathe more easily.