[ZODB-Dev] Re: so your coming from the rdbms world tutorial?

[Sean Allen]

On Mar 23, 2008, at 1:30 PM, Roché Compaan wrote:

> On Sun, 2008-03-23 at 11:38 -0400, Sean Allen wrote:
>> Can that be wrapped in a transaction so that if something goes wrong
>> with customer creation, the order gets rolled back as well?
>>
>> Or put higher level, do transactions only work within a single folder
>> or across folders?
>
> You can modify as many objects as you like in a transaction. Have you
> read the ZODB/ZEO programming guide yet?
>
> http://www.zope.org/Wikis/ZODB/guide/zodb.html

yes but the examples are always about objects in a single folder.
wasnt sure if different folders would have any impact.
i assumed not, but you know where assumptions get you.

>
>
>>>>> There is another good reason - it makes a lot more sense to
>>>>> distribute
>>>>> object creation to different containers in the ZODB to avoid write
>>>>> conflict errors.
>>>>
>>>> I think I understand this but can you elaborate?
>>>>
>>>> By 'distribute object creation to different containers' do you mean
>>>> store each
>>>> object in own folders?
>>>
>>> No that would lead to an unnecessary proliferation of folders and it
>>> wouldn't actually remove conflict errors.
>>>
>>> Conflicts errors occur when two concurrent transactions modify the
>>> same
>>> attribute. When you are putting objects in a folder you are
>>> essentially
>>> modifying the same attribute (unless you are using a btree). A good
>>> application design strategy for the ZODB is to ensure that  
>>> concurrent
>>> transactions are modifying attributes on different objects. If you  
>>> are
>>> putting all your orders in one folder you are increasing the chances
>>> of
>>> conflict errors.
>>>
>>
>> If you dont put all orders in a single folder, when it comes time to
>> search orders, how would you know where to find?
>>
>> Do you sequentially search the multiple folders for a given object?
>
> No. You index the order attributes that you want to search on and
> perform a search on the indexes. Have a look at zc.index and  
> zc.catalog
>
> http://svn.zope.org/zc.index/
> http://svn.zope.org/zc.catalog/
>
> I think you will also benefit a lot by looking at Zope as development
> platform. Have a look at the Zope3Book:
> http://wiki.zope.org/zope3/Zope3Book

I have not as it seemed rather Zope specific.
Are there particular parts I could zero in on as being particularly  
relevant?

When I review the index, there isnt anything that jumps out and says,
o read me. I have read the zodb/zeo guide as well as several other
things my googling turned up plus some misc other documents
from zope.org that seemed applicable.

The big problem I have is that all the zodb stuff i have found is
either very trivial or tied up zope. Zope by this point in time,
is a highly advanced and complicated system from the outside.
Having to slog through zope specific stuff trying to pick out
zodb details is frustrating.

If I go with zodb as a backend, I would intend to help others
who come in the future by providing more zodb specific
docs that arent at all tied to zope. ( I've actually come across
many blog point that make that specific point ).