Hi,

Christian Theune schrieb:
Hi,

On Feb 11, 2008, at 4:19 PM, Christian Theune wrote:
Context could be given as a reference date that is opaque to the
client
and can differ from storage to storage, a file pointer could serve
this
purpose. The API still might include the `length` of the data returned
to minimize round-trips.

Actually, a file position doesn't work either, because the storage
server can't know that much about what it is serving.

I would have thought that this wouldn't matter if we declare the context
`opaque`. As long as the storage can hand out a token that represents
context and that can be transferred through zrpc ...

I suspect the only sane approach is to make the storage server
maintain the iterator returned by the underlying storage on behalf of
the client.  This will cause resources to be allocated on the server
that might only be freed when the client disconnects.

Right, now this makes me feel uneasy. :)

We started sketching out what we need to do, but are blocked because we need to decide on the API

a) Do we want to change the iterator() method to not return an iterator but a list?

b) Can we add a new parameter to the iterator() method that limits the length of the list in addition to giving an upper bound through the stop argument?

Our proposal would be to:

def iterator(start=None, stop=None, count=None):
    """...

    If the count argument is not None, then iteration will end after at
    most `count` transactions.

    Returns a list of IStorageTransactionInformation objects.

    """


stop and count given together would limit the list to the condition that matches first.

Unfortunately this would mean:

a) a method called `iterator` does not return an iterator
b) an existing method changes its signature

The first effect is an argument for making ZEO work hard enough to pass the iterator through transparently.

The second effect (especially the count argument) is a functional requirement that we have, to be able to say `please give me 100 transactions` instead of providing a time frame with an unknown amount of transactions in it. This would be an argument for a new interface.

Anyway, we need to get consent first before going forward.

Christian

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