Re: Attempted Simultaneous Access causes "Could not lock file"

Thanks for your thoughful response, Vincent.

Presently I have one of the perl programs running collecting data and
storing it in my MSAccess database. It has been running since 11PM last
night.

I just wrote another test perl program and pasted in the massive SELECT
statement from my C# aspx code into the perl test code. The perl test code
runs fine.

Can we infer from this test that there is nothing wrong with the perl code
and there is something in my C#/ASPX connection string that needs
adjustment?

I also tried convering my aspx from ole to odbc. This did not help. The
symptoms are the same: no problem as long as perl is not writing to the
database.

Is this behavior new? Hmmm.... I've never been able to make simultaneous
access work between C# and Perl.

Any thoughts?

Thanks,
Siegfried


"Vincent Johns" <vjohns@xxxxxxxxxxxxxxxxxx> wrote in message
news:Px90f.5917$zQ3.5819@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> Siegfried Heintze wrote:
>
> > Hmmm.... the ASP.NET application is only reading.
> >
> > I can have multiple perl programs writing to the database,
simultaneously. I
> > wrote both programs. One of the most important features of a database, I
> > thought, was simultaneous access by multiple processes.
>
> No. Any simultaneous "write" access is only to different parts of the
> same database, such as separate records. If two processes attempt
> simultaneous changes to the same field, someone's work is likely to be
> trashed -- the field will contain only one value at the end, regardless
> of how many processes tried to change it.
>
> In Access, multiple processes might access separate records, but any one
> record is modifiable by only one process at a time, and it must release
> the record before the other process can change it. (It often doesn't
> even make sense for the 2nd process to have read-only access to the
> record, as the fields could easily be inconsistent up to the time the
> 1st process finishes writing and releases the record lock.)
>
> > The perl code is just doing "INSERT"s and the ASP.NET is only doing
Selects.
> > Is there not some setting that needs to be adjusted to allow multiple
> > readers and writers?
>
> I don't know, but my guess is that Perl needs to explicitly release each
> record after it finishes writing that record. Perhaps it's neglecting
> to unlock records.
>
> Is all this behavior new? If it is, did you change some of the code
> just before you noticed it? You might want to return to a previous
> version to try to identify the cause of the problem.
>
> > I understand that the MSAccess GUI needs exclusive access when editing a
> > table definition, but I'm not doing that.
>
> It probably needs exclusive access to the entire Table if it's modifying
> the Table's structure! I'd want exclusive access to the entire database
> if I were doing that, and for long enough to check the results for
> accuracy and consistency.
>
> But for editing the contents of a set of records, you probably need
> exclusive access only to the records being modified. Are you defining
> transactions on which you may at times perform Commit or Rollback
> operations? Any resources (e.g. records in Tables) involved in those
> will temporarily belong exclusively to some process, I expect.
>
> If the ONLY operation that any process wants to perform is reading, then
> there shouldn't be any need for any exclusive access. But you said that
> the Perl code is writing, too, so it does need to exclude other
> processes. I think the main question is how it's accomplishing that,
> and under what conditions it allows other processes to read.
>
> > Thanks,
> > Siegfried
> >
> >
> > "Vincent Johns" <vjohns@xxxxxxxxxxxxxxxxxx> wrote in message
> > news:qk5%e.1297$4h2.97@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> >
> >>Siegfried Heintze wrote:
> >>
> >>
> >>>I have a screen scraper written in perl that populates the same
database
> >>>every night with new additional information.
> >>>
> >>>Why is it that when I try to simultaneously write to the database with
> >
> > perl
> >
> >>>and read it with my ASP.NET UI I get "could not lock file" from
ASP.NET?
> >>>
> >>>Thanks,
> >>>Siegfried
> >>
> >>I don't know the details of your system, but this behavior seems quite
> >>reasonable. If ASP.NET needs exclusive use of some resource (such as
> >>your database), and some other process currently has access to the
> >>resource, then ASP.NET should definitely have to wait until nobody else
> >>is using it. Maybe you can schedule the activities for different times.
> >>
> >> -- Vincent Johns <vjohns@xxxxxxxxxxxxxxxxxx>
> >> Please feel free to quote anything I say here.


.

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