[ZODB-Dev] Relstorage Database Adapter

[Santi Camps]

On Wed, Nov 24, 2010 at 7:24 PM, Shane Hathaway <shane at hathawaymix.org>wrote:

> On 11/24/2010 05:17 AM, Santi Camps wrote:
>
>> Hi all
>>
>> I'm using relstorage for a long time with very good results.  Until
>> know, I also use database adapters like ZPsycopgDA to connect the same
>> SQL database and store information in other application tables.   I was
>> thinking to create a Relstorage Database Adapter able to do the work
>> using relstorage configuration and connections.   Some preliminary
>> simple tests seems to work:
>>
>> def execute_query(conn, cursor, *args, **kw):
>>     query = kw['query']
>>     cursor.execute(query);
>>     return cursor
>> query = 'SELECT COUNT(*) FROM kmkey_task'
>> rows = app._p_jar._storage._with_store(execute_query, query=query)
>> print rows.fetchone()
>>
>>
>> The question is, can I go on ?  Or use same connections than relstorage
>> could cause problems at ZODB level ?
>>
>
> Well, it doesn't look like you're using the two RelStorage connections the
> way they are intended to be used.  For the code snippet you gave, it's
> likely that you want to use the load connection rather than the store
> connection.
>
> The load connection ensures consistent reads.  RelStorage does a number of
> things to maintain that guarantee.  The load connection is never committed,
> only rolled back.
>
> The store connection is intended to be used only during transaction commit.
>  At the beginning of a commit (tpc_begin), RelStorage rolls back the store
> connection in order to get the most recent updates.  The store connection
> and load connection are often out of sync with each other, so code that uses
> the store connection should detect and handle conflicting updates.
>
> I suspect the load/store connection split is too complicated for most apps
> that just want to interact with the database, so I haven't exposed any
> documented API.  I considered making an API when I worked on
> repoze.pgtextindex, but I concluded that pgtextindex can be a bit lazy about
> consistency and therefore doesn't need all the extra complexity that reusing
> RelStorage connections would bring.
>
>
I understand it.   I will try to do it simpler:  create new connections
using relstorage connection string

Thanks a lot for your explanation.
-- 
Santi Camps
KMKey hacker (http://www.kmkey.com)
Earcon S.L. (http://www.earcon.com)
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