[ZODB-Dev] RelStorage: Which tables to replicate?

[Russ Ferriday]

Stefan,
Thanks for opening this thread here. I'm not actually doing anything  
like this, but it's great to see you pushing the envelop. I have done  
a lot of work on replicated data, over the years, that's where the  
following comment comes from.

On 22 May 2008, at 10:36, Stefan H. Holek wrote:

> We have put up two boxes in a MySQL master-master replication setup  
> [1]. As long as we only write to one of the masters all is fine.  
> Writing to both masters (and expecting MySQL to sort it out) is  
> giving us trouble. We see things like:
>
> Last_Errno: 1062
> Last_Error: Error 'Duplicate entry '41860' for key 1' on query.
> Default database: 'prod_zodb'.
> Query: 'INSERT INTO new_oid VALUES ()'
I have not read the reference, but it seems that this scheme can never  
work without keys (OIDs) being qualified by which master they  
originated on. Otherwise one of the mySQLs would need to be  
responsible for handing out unique oids.  You need an OID origination  
namespace for each master.

On the other issue, no idea.

Best,

--r.

>
>
> and
>
> Last_Errno: 1050
> Last_Error: Error 'Table 'temp_store' already exists' on query.
> Default database: 'prod_zodb'.
> Query: 'CREATE TEMPORARY TABLE temp_store
>       (
>        zoid        BIGINT NOT NULL PRIMARY KEY,
>        prev_tid    BIGINT NOT NULL,
>        md5         CHAR(32),
>        state       LONGBLOB
>       ) ENGINE MyISAM'
>
> Stefan
>
> [1] http://www.howtoforge.com/mysql_master_master_replication
>
>
> On 20.05.2008, at 18:36, Shane Hathaway wrote:
>
>> That is mostly correct.  You need to replicate transaction,  
>> object_state, current_object, and do something with new_oid.  There  
>> is no requirement to replicate the other tables, since they are  
>> used only for packing, although replicating object_ref and  
>> object_refs_added may save some work.
>>
>> The new_oid table is special to the MySQL adapter.  RelStorage uses  
>> the new_oid table as a kind of sequence.  Like any sequence, it is  
>> intentionally non-transactional.  Perhaps there would be no ill  
>> effects in switching it to the InnoDB engine.
>>
>> Which MySQL replication method are you looking into?
>
> --
> Stefan H. Holek
> stefan at epy.co.at
>
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Russ Ferriday - Topia Systems - Open Source content management with  
Plone and Zope
russf at topia.com - office: +44 2076 1777588 - mobile: +44 7789 338868 -  
skype: ferriday

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