topic Re: Read-only replicated server difficulties in Alfresco Archive

Read-only replicated server difficulties

johnwalsh — Tue, 26 Feb 2008 16:18:53 GMT

Hi,I have two Alfresco servers, and am using rsync and mysql replication to replicate the master to the slave. The slave is set to read-only. I'm running into a series of bootstrap problems where I need to change Java bootstrap routines to not do the bootstrap operation if the instance is in read-on

Re: Read-only replicated server difficulties

johnwalsh — Wed, 27 Feb 2008 20:20:14 GMT

It looks to me like repository replication can't work. The wiki sure seems to state that it does, and I'd sure like to be wrong wrong:

My slave instance is now proceeding through the boot process as far as the ModuleComponentHelper where the custom modules are started up. (I have two custom modules.) That work is done within a transaction. The attempt to get a transaction was failing because I have transactions configured to readOnly. My code can't skip custom module startup and still behave as desired, so I changed RetryingTransactionHelper to return a read-only transaction instead of failing when a read-write transaction is requested but the RetryingTransactionHelper's readOnly flag is set to true. My hope was that no writes would be required for the slave Alfresco instance. Unfortunately, that's not true. The following line in ModuleComponentHelper.startModule() attempts to write to the database and fails:

registryService.addProperty(moduleKeyCurrentVersion, moduleNewVersion);‍

This makes it appear that the system has to be allowed to write to the database if you need to include custom modules. For reasons documented in my previous post (conflicting primary key values), the slave in a replicated system cannot be allowed to write to the database. These conflicting truths seem to imply that Alfresco repository replication can't work if you have custom modules.

Does anyone have it working? How did you address slave writes to the database with MySQL replication of the database?

I hope I'm missing something, because repository replication is a really desirable feature. Any help would be appreciated.

Thanks,
John

Re: Read-only replicated server difficulties

johnwalsh — Tue, 11 Mar 2008 03:51:23 GMT

I haven't gotten any further with this. Any help would really be appreciated.

Re: Read-only replicated server difficulties

cbosdonnat — Thu, 05 Jun 2008 06:15:44 GMT

Hi John,

Is there a simpler way to make Alfresco replication with a read-only slave work? Have others done this?

Yes there is an easier way to do this. Just have a look at this article I recently wrote:
http://cedric.bosdonnat.free.fr/wordpress/?p=87&lang_view=en

The principle is easy: just turn the transactions as read-only, but not using a config file. This way you can turn Alfresco in a read-only mode without having to restart it. Then all the problems of data written at the startup can be forgotten. To turn your Alfresco read-only or read-write is then only one HTTP request.

I hope this helps

Re: Read-only replicated server difficulties

johnwalsh — Thu, 05 Jun 2008 13:24:36 GMT

Cedric,

Awesome. Thanks. You can do a lot with Alfresco, if you know where to look for inspiration. Nice sleuthing!

Thanks again,
John

Re: Read-only replicated server difficulties

janv — Thu, 05 Jun 2008 16:24:22 GMT

For reference, it is also possible to use JMX to set read-only mode, if you're using 2.2, 2.9C-dev or HEAD.

Regards,
Jan

Re: Read-only replicated server difficulties

cbosdonnat — Fri, 06 Jun 2008 05:28:25 GMT

Hi Jan,

For reference, it is also possible to use JMX to set read-only mode, if you're using 2.2, 2.9C-dev or HEAD.

That reminds me to have a serious look at JMX… Thanks for the info.

Cedric