concurrent access to dbms (was best way to store dbm records?)

[Michael B. Allen]

Shelve works great Tim, thanks. I have implemented this and it works very
well for my purposes.

I may have a different issue however. The docs on shelve(and I would imagine
dbm's in general) report that you cannot concurrently read from it if it is
open by a writer. If I have interpreted the docs correctly this is true even
if it is only open by a single writer.

Can I have may readers with one writer or might this corrupt the database?.
Or in the worst case will it mearly display possibly incomplete information
to a reader?

In my case I don't care if readers get realtime info. Can I just
periodically make a copy of the dbm for readers?

Also, how many records can I put in a dbm without taking a big performance
hit? 10000?

Thanks,
Mike


Tim Roberts wrote in message <9f2vtss06scg26psv7gvfv8agt68jc91h3 at 4ax.com>...
>"Michael B. Allen" <mballen at NOSPAM_erols.com> wrote:
>>Hi!
>>
>>I was wondering what the best/simplest way to store dbm records is? This
is
>>how I am currently adding records:
>>
>> # create dbm record
>> p = '102'
>> s = getfield(msg, 'from')
>> a = getfield(msg, 'authors')
>> v = getfield(msg, 'version')
>> d = getfield(msg, 'description')
>> x = getfield(msg, 'fixes')
>> o = getfield(msg, 'obsoletes')
>> r = getfield(msg, 'requires')
>> f = getfield(msg, 'flags')
>> dbmrecord = (a,v,d,x,o,r,f)
>> db[p] = `dbmrecord`
>
>A shelve can do this all for you.  A shelve is just a dbm that holds
>pickled objects.  Create a class to hold the data:
>
>  class EMailIndex:
>    self.key = ''
>    ...
>
>  fields =

>    'from',
>    'authors',
>    'version',
>    'description',
>    'fixes,'
>    'obsoletes',
>    'requires',
>    'flags'
>  )
>
>  idx = EMailIndex()
>  idx.key = '102'
>  for name in fields:
>    idx.__dict__[name] = getfield(msg, name)
>
>  db = Shelve.open( dbname, 'w' )
>  db[idx.key] = idx
>  db.close()
>
>Later, you can get the object back intact.
>
>  >>>db = Shelve.open( dbname, 'r' )
>  >>>xxx = db['102']
>  >>>xxx.authors
>  ds-0.1
>
>--
>- Tim Roberts, timr at probo.com
>  Providenza & Boekelheide, Inc.