Re: Locking/Concurrency Options

Question

Hi,
A really real life question. Just one question ... Did you check on the
performance? Cause what you end up here in option 2 is doubling the SQL in each
update.
Agree?
[email protected] wrote:
The options described in the recent messages are pretty well-known..
The way I look at it, unless you use some sort of active
locking/notification, you end up with one of two types of update:
Last Write Wins - No last-minute checking at all for timestamp
discrepencies, etc. Last update overwrites any previous changes.
First Write Wins - Check a timestamp or version number on the row and
disallow changes for subsequent users at commit time.
I ran in to a situation where we needed to simulate Last Write Wins on an
individual FIELD level, rather than row level.. In other words, two people
bring up the same Customer object on the screen, one person changes the
Phone Number and saves, and the other person updates the Zip Code and saves.
Both changes are reflected in the database.
Option 1:
When you make changes to attributes in the business object, keep track of
what you change and at commit time create a dynamic SQL statement which
updates only those columns in the table. Given that I dislike dynamic SQL
vehemently (has to do with Oracle parsing and the search/LRU algorithms in
the shared pool) I could not do it this way..
Option 2:
When you make changes to attributes in the business object, again keep track
of what you change. During commit, start a transaction and read the current
row "for update" in to a temporary object. Copy the modified data from the
real object in to the temporary object and write the temporary object back
out. Avoids dynamic SQL since both the select for update and the update
statement read/write every column and never change.
Comments?
Anyone have a better idea?
-Greg
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Answer 1

Hi again,
It is solved. I was getting a 0x24 error, which I couldn't see before because the report error was disable.
I've downloaded the Windows Vista Recovery Disc available [here|http://neosmart.net/blog/2008/windows-vista-recovery-disc-download/] and it recovered the system.
For safe I'm making a DVD recovery now. I didn't know this laptop had a recovery system only inside the HD.
Thanks