objectbridge-developers

[OJB-developers] Smart Updates

[Darren S. <dsy...@ci...>]

I seem to remember testing a version of Object Bridge 0.7.235 that performed
smart (or tuned) updates - only updating columns that had been modified.
The documentation which came with this version mentioned this feature in a
performance comparison with EJB.

I'm writing some test code with the 0.7.310 and I can't see any reference to
smart updates.  When I turn on SQL logging I only see a prepared statement
that updates all columns.

Have I missed anything ?


Thanks
Darren

Re: [OJB-developers] Smart Updates

[Thomas M. <tho...@ho...>]

Hi Darren,

Darren Syzling wrote:

> I seem to remember testing a version of Object Bridge 0.7.235 that performed
> smart (or tuned) updates - only updating columns that had been modified.
> The documentation which came with this version mentioned this feature in a
> performance comparison with EJB.
>


These "Smart Update" feature has been kicked out a long time ago. May be 
it was still mentioned in the performance comparison. (I kicked out this 
documents as it is over a year old and totally out of date).

At the time of "smart updates" OJB did even use prepared statements. We 
used dynamically generated SQL that was generated for each update. No 
parameter binding. No caching of prepared statement.

Now OJB is working with prepared statements and uses a caching mechanism 
for these statements.
This setup brings an enormous performance gain for most application 
scenarios against most RDBMS.

Of course it would even be better to still have a smart update 
mechanism. but this would require to cache much MUCH more statements.
For N columns there are (if I remember correctly) (2^N) - 1 possible.
For a table with 10 coulums we had to cache more then 1000 statement !

That's why I dropped this feature.
My performance tests showed that using the cached prepared statement 
instead of dynamic "smart updates" has a much better performance.

 
HTH,


Thomas

Re: [OJB-developers] Smart Updates

[Darren S. <dsy...@ci...>]

Thomas,

> These "Smart Update" feature has been kicked out a long time ago. May be
> it was still mentioned in the performance comparison. (I kicked out this
> documents as it is over a year old and totally out of date).

You're right I found no reference to the EJB comparison in the latest
distribution.

> Now OJB is working with prepared statements and uses a caching mechanism
> for these statements.
> This setup brings an enormous performance gain for most application
> scenarios against most RDBMS.

I suspected this may be the case but wanted to hear you say it :-)

> That's why I dropped this feature.
> My performance tests showed that using the cached prepared statement
> instead of dynamic "smart updates" has a much better performance.

Good, that's the kind of anecdotal evidence I was looking for.  If prepared
statements negate the performance improvement made by smart updates then for
the kind of work I'll be doing this should be fine.  If I find any problems
I'll report back...



Darren

[OJB-developers] How to map a float to MySql?

[<ri...@ya...>]

Hi,

How do you map a float value to a MySql table field?

The OJB documentation says that you should map float values to a REAL =
column
in the database, but MySql doesn't have that sort of data type.

First, I defined the MySql field as FLOAT(4,2).

Then I tried to map the float value to a REAL column, in the mapping.xml =
file,
but OJB expects a double value:

[ojb.broker.accesslayer.RsIterator] ERROR: null
java.lang.Double
at =
ojb.broker.accesslayer.RowReaderDefaultImpl.readObjectFrom(RowReaderDefau=
ltI
mpl.java:77)
...

I've tried to map it to a FLOAT column in the mapping.xml file, but I =
receive
the same exception: OJB is expecting a double.

For all these changes, my database field was defined as FLOAT(4,2). =
Should I
change this?

Has anybody mapped a float to a MySql database?

Thanks in advance.

Ricardo Arguello