c2c-oerpscenario team mailing list archive

[Raphaël Valyi - http://www.akretion.com <746620@xxxxxxxxxxxxxxxxxx>]

On Thu, Jun 2, 2011 at 12:33 PM, Olivier Dony (OpenERP) <
746620@xxxxxxxxxxxxxxxxxx> wrote:

> [...]
>
> For case 1, different strategies have different properties, as
> illustrated in the comparison I am attaching to this bug. Using SELECT
> FOR UPDATE with the NOWAIT flag is basically a pessimistic locking
> strategy with immediate conflict detection. This looks to me like the
> best strategy when you know all transactions are going to update the row
> in the same way, which is the case for ir.sequence. With this strategy
> you prevent transactions to even read the about-to-change value (making
> sure it cannot be used erroneously to produce a report, an email, etc.
> before detecting the conflict), and you also detect the conflict
> immediately, instead of waiting a bit to fail later anyway.
>


Olivier, sorry, I still don't get it:
if the sequence is locked by some batch (like the MRP), what is the benefit
of "not waiting even a second before failing".
Can you cite a use case where there is a benefit in not waiting even for a
second?

You say: " instead of waiting a bit to fail later anyway."
If take the MRP batch case or other batches like we have with
base_sale_multichannels,
there is often a commit after a record is processed, and I believe this is a
good practice as it would prevent a full roll back just because of some
specific record issue.
Since there are commit and since the batch spend time doing other things*
before locking the ir_sequence table, unless I miss something it means that
there are small time periods while the ir_sequence is not locked. Am I
wrong?
Then, unless I miss something, if we wait say up to 1 sec when requesting a
sequence number, wouldn't have get a chance to be able to get our sequence
number during those small periods it's not locked?
And overall, what is the benefit of waiting 0 millisecond before blowing
into a locked sequence table exception? Any use case where this really bring
value?

Thanks.

* I even consider very seriously to introduce some sleep(a few millisecs) at
least in base_sale_multi_channels import batches if that would help making
other process more fluid (and so may be we could optionally do it in the MRP
batch too).

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https://bugs.launchpad.net/bugs/746620

Title:
  Implementation of faster gap-tolerant sequences

Status in OpenERP Server:
  Confirmed

Bug description:
  OpenERP is classified as an Enterprise class software package. Meaning
  that more than one person, at least 2 should be able to use the system
  simultaneously. Like packers shipping products, taking orders,
  reserving products. I find that in fact, it is not possible for
  creation of stock moves simultaneously.

   Say I am importing orders from a shop. It is creating stock moves  because the order is paid. 
  At the same time I am shipping products which is normal for an ERP system.
  I might also import orders from a separate shop say a POS system.
  It is not possible!
  [2011-03-31 13:10:47,657][midwestsupplies] WARNING:stock.location:Failed attempt to reserve 1.0 x product 1669, li
  kely due to another transaction already in progress. Next attempt is likely to work. Detailed error available at D
  EBUG level.  
  OperationalError: could not obtain lock on row in relation "ir_sequence"
  Two different errors.
  I  can only perform one action at a time!
  What happens is that any time the program calls for a stock_move it will lock the stock_move table so no other process can access it which means that you cant do hardly anything unless its done individually. Now say with a MS system, or any Enterprise system would be able to handle many simultaneous actions but this program has a serious architecture flaw to not be able to support this.