We need to prevent multi-user access to the SQL backend (Re: New GnuCash article on LWN)

[Per Kjeldaas]

Tao,

Your solution to block the whole database is good enough for me.

Thanks,
Per.

On May 19, 2010, at 2:26 PM, Tao Wang wrote:

> On Wed, May 19, 2010 at 6:58 PM, Christian Stimming <stimming at tuhh.de> wrote:
>> 
>> The article raises one valid serious concern: The database backend does
>> nothing to prevent multiple user access. This is bad because simultaneous
>> access to the SQL database from multiple users will almost surely cause data
>> loss. On the other hand, the technology term "SQL backend" will almost
>> surely raise the user expectation that multiple user access were possible,
>> so for sure people will give it a try. Since it will corrupt their data, we
>> need to build in some prevention measure - the equivalent of the "lock
>> file", but inside the SQL database. Ideas, anyone?
>> 
> 
> Create a table in database, and
> 
> 1) insert a entry contains a GUID of current user/process/computer
> when GnuCash is loading the database.
> 2) remove the entry when it exit.
> 3) Let user decide whether force to overwrite the entry the entry
> exist, such as last time GnuCash crashed, or there is another process
> is using it.
> 4) Read the entry everytime GnuCash is accessing the database, to make
> sure it's not overwrite by others.
> 
> Instead of the lock of whole database, another solution is recording
> locks of each entity/object in the table, everytime user trying to
> edit something, gnucash create a lock(a entry of the lock_table) on
> the object, and any other user trying to edit that object will get a
> warning, and will not be able to edit the object unless the previous
> user release the lock.
> 
> -- 
> Regards
> 
> Tao Wang
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