Ed,
If you use the highest synchronization level (Serializable), then component
A locks the record when it reads it. Therefore component B can't read the
record from the database until A has completed its transaction and released
the lock.
Anne
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]
Sent: Sunday, April 04, 1999 5:47 PM
Subject: Lost Updates and EJB
Hi all,
I've been dusting off my old database book recently, and I've run into
an
interesting problem in transactions -- the Lost Update. A lost update
occurs in
a scenario such as the following. Assume two components A and B
concurrently
perform these operations:
1 Component A reads integer X from the database. The database now contains
X =
0.
2 Component B reads integer X from the database. The database now contains
X =
0.
3 Component A adds 10 to its copy of X, and persists it to the database.
The
database now contains X = 10.
4 Component B adds 10 to its copy of X, and persists it to the database.
The
database now contains X = 10.
Thus Component A's update has been lost.
Can someone reason to me which EJB transaction isolation level(s) explicitly
protect against Lost Updates, and how it protects against them?
Thanks
-Ed
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