Thank you all,
It turned out that combining SELECT FOR UPDATE and isolation_level
SERIALIZABLE and pyramid_tm 0.8 produced the expected result. IOW:
everything is now working correctly:
The only change to history_meta.py we ended up doing was the following:
```
#attr['version'] = obj.version
session.query(obj.__class__).with_for_update().filter(obj.__class__.id
== obj.id).one() #S1
version_number =
session.query(obj.__class__.version).with_for_update().filter(obj.__class__.id
== obj.id).one() #2
attr['version'] = version_number
```
Though we haven't tested extensively, we suspect that between 'SELECT FOR
UPDATE' S1 and S2, only S1 is needed.
Thanks again.
On Thursday, December 4, 2014 8:55:59 PM UTC-6, kirk holland wrote:
>
> Hi,
>
> We were having a similar problem with history_meta, so we created
> history_meta_date (.py file attached). In our version, we use timestamps
> rather than sequence numbers to track history versions and don't need to
> worry about duplicate key problems. The "version_date" timestamps still
> provide sortability on version, but are infinitely less likely to have the
> same value issued to separate processes.
>
> Disclaimer: The attached file was developed in a hurry to solve an urgent
> problem, it has performed well for us, but probably hasn't gone through the
> testing rigours that this group might expect. Feel free to use/adapt it as
> necessary and if you have the time/inclination, post a more rigorous
> version for consideration as a formal recipe.
>
> Cheers
>
> ---------- Forwarded message ----------
> From: HP3 <henddher...@gmail.com <javascript:>>
> Date: 5 December 2014 at 10:36
> Subject: [sqlalchemy] history_meta.py IntegrityError: (IntegrityError)
> duplicate key value violates unique constraint "p2docs_history_pkey"
> To: sqlal...@googlegroups.com <javascript:>
>
>
> Hello all,
>
> We are facing a problem when using history_meta.py recipe.
>
> It seems like two concurrent transactions read the same (id,version) tuple
> at "#1" and then each one tries to insert a new row into the pbases_history
> table with the same pk (id, version) combination (see #2)
> By removing #2, the issue goes away but of course, there is no history
> kept anywhere.
>
>
>
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