Hi Tim,

I've got a couple of questions regarding the locking:

1) I was wondering, if there were a number of users connected to a database,
and some were using opportunistic locking, and the others pesamistic
locking - what happens if two people using different locking methods try and
edit the same record?


2) If I use opportunistic locking - is there a way to notify a user that
someone else is editing the same record before they go into edit mode. (I
have a situation where we want to be able to use opportunistic locking so if
someone crashes out, it doesn't leave a record locked - however I also want
to warn a user if they start editing a record that is currently being edited
by another user - with the option to ignore, or cancel).

Thanks & Regards

Adam.

Adam,

<< 1) I was wondering, if there were a number of users connected to a
database, and some were using opportunistic locking, and the others
pesamistic locking - what happens if two people using different locking
methods try and
edit the same record? >>

They will both be allowed to edit the record, but the one using optimistic
locking will get an exception during the Post if the one using pessimistic
locking posted changes to the record.   If the one using optimistic locking
tries to Post the record while the one using pessimistic locking is still
editing the record, then the optimistic user will get a record lock
exception.   The bottom line is that optimistic locking user usually loses
to the pessmistic locking user in most cases.

<< 2) If I use opportunistic locking - is there a way to notify a user that
someone else is editing the same record before they go into edit mode. (I
have a situation where we want to be able to use opportunistic locking so if
someone crashes out, it doesn't leave a record locked - however I also want
to warn a user if they start editing a record that is currently being edited
by another user - with the option to ignore, or cancel). >>

The only way to know for sure is to try and lock the record, and then you
basically have pessimistic locking again.

The best way to solve the above is to set low connection timeout (but higher
than the ping interval used by the remote sessions) and dead session
expiration values on the database server and use pinging with the remote
sessions.    That way any dead sessions will get cleared rather quickly.

--
Tim Young
Elevate Software
www.elevatesoft.com

"Adam H." <ahairsub4@rREMOVEMEspamSTOPPER.jvxp.com> wrote in news:7E251F92-
4D3B-4B98-8F64-2B1ED7B90D33@news.elevatesoft.com:

>  is there a way to notify a user that
> someone else is editing the same record before they go into edit mode

One idea I've used for other purposes, but not for this:

if you use a positive integer as the primary key, then before you start
editing insert a copy of the record into the same table with the key
"negativised".

Before you allow anyone to modify a record, check whether the negative
record is there.

After you've posted or cancelled the update, remove the negative version.

free bonus:
If you add an extra field you can put the current user's name in there,
which can be used to remind them what they were doing if the PC crashed
while they were modifying the record.  The negative record's still there
when they open the table next time, and it's got their name in it...

2nd free bonus:
If you let them modify the negative version, updating it with EVERY field
change as they do it, and overwrite the positive one at the end, then they
get all their work-in-hand back after a crash.
--
Chris
(XP-Pro + Delphi 7 Architect + DBISAM 4.25 build 4 + EDB 1.04 build 3)

Hi Chris

You have some good suggestions there. Thanks for sharing them with us!

Best Regards

Adam.