[Pvfs2-developers] TroveMethod configuration parameter

[Sam Lang]

On Nov 28, 2006, at 9:01 AM, Phil Carns wrote:

> I have some questions about the TroveMethod parameter.
>
> It looks like it can be specified either in the <Defaults> section  
> or the <StorageHints> section.  I added some gossip prints to  
> Trove's initialize() and collection_lookup() functions to see what  
> these correspond to:
>
> - TroveMethod in <Defaults> toggles the value passed to initialize()
> - TroveMethod in <StorageHints> toggles the value passed to  
> collection_lookup()
>
> Both of these default to "dbpf" if not specified in the  
> configuration file.
>
> Is the collection_lookup() value (and therefore the <StorageHints>  
> section of the config file) the one that actually impacts I/O in  
> the server?  I am assuming so, because you may have multiple  
> collections and it makes sense to be able to specify a different  
> method for each one.
>
Hi Phil,

The main issue here is that the trove initialize doesn't know which  
method to use, so there needs to be a global default.  Each  
collection also gets its own method as you've noticed, so you can  
specify that on a per collection basis.


> The pvfs2-genconfig utility places TroveMethod option in the  
> <Defaults> section.  Is this intentional?  For example, if someone  
> edited a configuration file created by genconfig, they might try to  
> change the value of TroveMethod from "dbpf" to "alt-aio".  However,  
> it doesn't look like this would have any real impact.  It would  
> change the parameter to trove's initialize() function, but the  
> collection_lookup() would still default to the dbpf method.

Hmm.. that's true.  The config format and the trove interfaces don't  
match up real well.  Ideally, there wouldn't be a TroveMethod in the  
<Defaults> section at all, and the trove initialize would work on a  
per-collection basis, but right now we store collection info in both  
the config file and inside the collections database.  To be able to  
open and read from the collections database, we need a trove method.

Maybe it makes sense to use the default from the <Defaults> section  
if one isn't specified for that collection?  I'm not crazy about this  
solution but it seems like a reasonable alternative.

-sam

>
> -Phil
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