[Mulgara-dev] Autocommit off, session abandonment and database mirroring

[Paul Gearon]

Not knowing the specific code in question, I CAN tell you that it  
makes no sense for a transaction to be basing idle time on the time  
between issued queries.  Loading large quantities of data will also  
take a long time, and I know that we didn't timeout while this was  
happening.

Unfortunately, I know next to nothing about JOTM.  I quickly perused  
the code, and it appears that the timeout stuff is all handed off to  
a transactions coming from the org.objectweb.transaction area.  From  
the lack of anything else, it seems that this class is expected to  
throw an exception when a timeout occurs.  I also can't see where the  
transaction gets told that operations are occurring (hence resetting  
the timeout).  Hopefully Andrae can elucidate (as I'd like to know  
myself).

No, there is no mirroring in Mulgara.  This is something we hope to  
introduce at Fourth Codex (where I work).

In the meantime, I'd say the easiest way to make it work would be via  
a resolver that writes to a peer server at the same time (maybe the  
server names are configured in the system resolver.  Maybe it's just  
coded into a boot-time config file), and reads get handled via  
Piranha on Linux (http://sourceware.org/piranha/).

I'm not very helpful today, am I?  Sorry.  :-)

Paul

On Apr 6, 2007, at 1:54 PM, David Moll wrote:

> Gents,
>
>
>
> We (those of us at Viewpoint) have a question about some of the  
> documentation for Mulgara.  Specifically the part that says:
>
>
>
> If a session with autocommit set off is idle for a period greater  
> than three minutes, and a second session attempts a write, then a  
> rollback of the first session's uncommitted transactions occurs.  
> The first session's next iTQL command then reports an error  
> indicating that the transactions were lost.
>
>
>
> What does “idle” mean in this context?  We do have queries that  
> take much more than three minutes, especially deletes.  I can see  
> two possibilities.  “Idle” could mean that no new queries have  
> happened in three minutes, so the next session that sends a query  
> requiring a write lock will cause an abandonment of the first  
> session’s query.  The other possiblity is that “idle” means that  
> the metastore itself is idle, so if there is a query running which  
> takes 10 minutes to complete, it would not be in danger of being  
> abandoned until time t0 + 10 minutes + 3 minutes.
>
>
>
> Also, is there mirroring functionality in Mulgara?  Specifically,  
> we are looking to have two identical metastores set up so that if  
> the primary goes down when doing some particularly heinous iTQL  
> query (I know we have one that returns a 14MB XML string), we can  
> immediately switch to querying against the secondary without  
> skipping too many beats.  At the risk of making Paul weep, we are  
> still using TKS 2.1 for our live production server.  There is  
> active development in migrating that project to Mulgara, but we  
> haven’t gotten to that point yet.
>
>
>
> As always, thanks for listening,
>
>
>
> David Moll
>
> Software Engineer
>
> dmoll at www.viewpointusa.com
>
> Viewpoint Data Management LLC
>
>
>
>
>
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> Mulgara-dev at mulgara.org
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