[pmwiki-users] Avoiding simultaneous edits

Patrick R. Michaud pmichaud at pobox.com
Wed Sep 20 11:06:16 CDT 2006

On Wed, Sep 20, 2006 at 09:09:40AM -0500, Ben Stallings wrote:
> I set up a wiki for a University class to use in their group projects, 
> at http://www.abundance-ecovillage.com/EnergyCourse .  
> They're having trouble now with simultaneous edits.  I had expected that 
> the wiki would tell them when they tried to overwrite each other's work 
> -- I've seen that message often enough just working on my own!  But it's 
> not doing that... it just cheerfully overwrites any changes that have 
> been made by other users.  My question: Is this due to...
> a) the fact that they're not using Author names
> b) the fact that they're on a Wi-Fi network and so all have the same IP 
> address
> c) the combination of a) and b)
> d) some bug (or new feature I was unaware of!) in version 2.1.24

I'm guessing

    e) the site isn't merging edits properly

The problem can't be (a), (b), or (c); PmWiki doesn't use author
names or IP addresses to determine when a simultaneous edit
occurs.  PmWiki uses timestamps embedded in the edit form to
figure out if a page has been modified while someone is editing it.

I went to the WikiSandbox on the site and tried doing a simultaneous
edit, and PmWiki correctly flagged my second post with the
simultaneous edit warning.  However, it *didn't* merge the changes
into the post, so if I were an author I would look over the
page, not see any conflicts, and just save it again (thus overwriting
previous authors' changes that occurred during my edit).

Is this running on a Windows platform?  You may need to install
the recipe at http://www.pmwiki.org/wiki/Cookbook/SimultaneousEdits
to enable merging since diff3 isn't present.

Is this running on a Unix platform?  You may need to check that
the diff3 program exists or that PmWiki is able to locate and
run it (PmWiki typically looks for /usr/bin/diff3).  If it's in
a different location, you'll want to set $SysMergeCmd appropriately;
if for some reason it cannot be executed (e.g., safe_mode is
enabled), then you might try the cookbook recipe above.

(The cookbook recipe can be a lot slower than the external
program, plus I'm a little concerned about the memory use of
the recipe.)

Hope this helps,


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