Re: 2 Macs -- 1 File
- From: zoara <me18@xxxxxxxxxxx>
- Date: 20 Jan 2011 16:09:06 GMT
David Empson <dempson@xxxxxxxxxxxxx> wrote:
zoara <me18@xxxxxxxxxxx> wrote:
Chris Ridd <chrisridd@xxxxxxx> wrote:
On 2011-01-18 15:11:46 +0000, zoara said:
What exactly doesn't Filemaker like about being opened via File Sharing? Or
is it just the possibility of having two concurrent users attempting to
access the database file?
Most databases hate that sort of thing. They assume they're the only
process writing to a given binary file (the DB), and will generally freak
out if something happens to it without them being involved.
But that problem isn't restricted to databases. Any file at all will
potentially suffer problems if two processes get to dick about without
knowing about each other or sharing a commonly-agreed method of interacting
with the file. Two versions of Photoshop editing the same image at the same
time is asking for trouble.
Sure, so you might overwrite editing changes in a single image file on
one computer with those made on another computer.
Yup. But not quite what I was thinking - see below.
Is there something worse than that going on with Filemaker?
Potential corruption of the entire database file if it is modified by
two computers at once, due to issue like rearranging data within the
file in different ways or moving indexes without knowledge of the other
copy. How much data do you want to risk?
Hmm. So... In the Photoshop case you just end up with an overwrite, but in
the Filemaker case you get complete corruption? Why? Seems like in one case
the data is atomic (you write it out all at once) whereas in the other it
isn't (you can write partial stuff back). In which case my example was
poor; I'd assumed Photoshop was non-atomic. So let's just assume I'd used
an example of an app that writes parts of files back and not the whole
thing at once; perhaps plists are a better example as they can be written
non-atomically. Can't they?
But my point was that you risk losing data, through whatever mechanism, if
you concurrently edit the same data with two apps that aren't aware of each
There is a secondary issue: FileMaker doesn't trust network file systems
for database access, due to the risk of loss of connection or buggy
network protocols, either of which could corrupt the database.
Aha. Now *that* I hadn't thought of. Shared file systems are riskier. Yup.
FileMaker Pro has its own networking protocol which is designed to
minimise or eliminate these risks.
You use it with two copies of FileMaker Pro: one hosting the dataabase
and sharing it to network clients, and the other connecting to the host
over the network. The host deals with contention issues (e.g. both users
can't modify the same record at the same time) and is responsible for
maintaning the internal structure of the database file. The client
doesn't get access to the raw file.
There is also a FileMaker Server product which is better for dealing
with a moderate to high number of users, and adds features like being
able to back up a live database.
All of those are how I would expect this sort of app to behave, but I was
coming at it from the other direction - why was it extra-unwise to point
two copies of Filemaker at the same file versus two copies of other types
email: nettid1 at fastmail dot fm
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