JDBC - multiple database

[cmk128]

Hi
If i invoke a select statement through JDBC, can JDBC send that to
two different databases and combine the results for me?

thanks
from Peter ([email protected])

 

[hvt]

Hi
If i invoke a select statement through JDBC, can JDBC send that to
two different databases and combine the results for me?

thanks
from Peter ([email protected])

yep, this cud be done though u need to maintain two diff connection
and statement instances to invoke jdbc query on two different
databases.

 

[Lew]

yep, this cud be done though u need to maintain two diff connection

Please don't use such terse abbreviations. "Cud" is regurgitated grass that
cattle chew. "diff" is a UNIX utility. "u" is a type of turn made by an
automobile.

and statement instances to invoke jdbc query on two different
databases.

That really depends on what you mean by the word "database". For example, in
systems that have a "CREATE DATABASE" command you might be able to access more
than one "DATABASE" through a single connection. Such systems refer to tables
with a "database.table" syntax. You can even refer to multiple "DATABASEs" in
the same SQL statement.

- Lew

 

[Guest]

If i invoke a select statement through JDBC, can JDBC send that to
two different databases and combine the results for me?

Only if the the database server the statement is connected to
via a connection supports the usage of remote/linked database
servers in its SQL dialect.

Arne

 

[hvt]

Please don't use such terse abbreviations. "Cud" is regurgitated grass that
cattle chew. "diff" is a UNIX utility. "u" is a type of turn made by an
automobile.


That really depends on what you mean by the word "database". For example, in
systems that have a "CREATE DATABASE" command you might be able to access more
than one "DATABASE" through a single connection. Such systems refer to tables
with a "database.table" syntax. You can even refer to multiple "DATABASEs" in
the same SQL statement.

- Lew

lew thx fr ur suggestion and all those dictionary explanations!!!

 

[Lew]

lew thx fr ur suggestion and all those dictionary explanations!!!

THX is a format for home stereo sound.
<http://www.practical-home-theater-guide.com/thx-home-cinema.html>

Seriously, it is a good idea to practice using full words and good grammar.
here It will help you when you want to impress folks in the work world. Also
it is much easier on other people in the newsgroup, especially the
international community who may not have the immersion in American-style
cell-phone textspeak
<http://en.wikipedia.org/wiki/Newspeak>
to help them read your posts.

If your goal is to communicate. If not, then gradually you might find less and
less useful response as people give up trying to adapt to the difficult text.


Dz th hp u?

Gosh, even I don't know what I just said. ;-) LOLLIGAG. WTF?

<http://en.wikipedia.org/wiki/Leetspeak>

- Lew

 

[Martin Gregorie]

Please don't use such terse abbreviations. "Cud" is regurgitated grass
that cattle chew. "diff" is a UNIX utility. "u" is a type of turn made
by an automobile.


That really depends on what you mean by the word "database". For
example, in systems that have a "CREATE DATABASE" command you might be
able to access more than one "DATABASE" through a single connection.
Such systems refer to tables with a "database.table" syntax. You can
even refer to multiple "DATABASEs" in the same SQL statement.

'hvt' is dead wrong if transaction integrity is important to the OP.

Unless you're using a transaction manager you can't guarantee that work
units on the separate databases are all either committed or rolled back.
Examples of this sort of framework are Pathway for HP's Guardian NonStop
OS, BEA's Weblogic and IBM's MQ series.

I don't think there's any such mechanism built into Java though I'll be
happy to hear that I'm wrong.

 

[hvt]

THX is a format for home stereo sound.
<http://www.practical-home-theater-guide.com/thx-home-cinema.html>

Seriously, it is a good idea to practice using full words and good grammar.
here It will help you when you want to impress folks in the work world. Also
it is much easier on other people in the newsgroup, especially the
international community who may not have the immersion in American-style
cell-phone textspeak
<http://en.wikipedia.org/wiki/Newspeak>
to help them read your posts.

If your goal is to communicate. If not, then gradually you might find less and
less useful response as people give up trying to adapt to the difficult text.

Dz th hp u?

Gosh, even I don't know what I just said. ;-) LOLLIGAG. WTF?

<http://en.wikipedia.org/wiki/Leetspeak>

- Lew

lew i appreciate your and other group members concern over language
used in the forum.

Martin, as the question was posted:
can JDBC send that to two different databases...
this can be done by maintaining two different connection/statement
object. I 've tried this for searching Weblogic portal repository and
local application data through Lucene. Weblogic maintains it's portal
repository data in pointbase (default database) and local application
data was maintained in Oracle9i.
If you see any problem in this please clarify.

Now seeing this as how feasible is this approach for processing data
through multiple databases, a solid framework is required (completely
agree).

 

[Guest]

Unless you're using a transaction manager you can't guarantee that work
units on the separate databases are all either committed or rolled back.
Examples of this sort of framework are Pathway for HP's Guardian NonStop
OS, BEA's Weblogic and IBM's MQ series.

I don't think there's any such mechanism built into Java though I'll be
happy to hear that I'm wrong.

All J2EE app servers has a built in transaction manager that can
handle multiple XA compliant databases.

Arne

 

[Martin Gregorie]

Martin, as the question was posted:
can JDBC send that to two different databases...
this can be done by maintaining two different connection/statement
object. I 've tried this for searching Weblogic portal repository and
local application data through Lucene. Weblogic maintains it's portal
repository data in pointbase (default database) and local application
data was maintained in Oracle9i.
If you see any problem in this please clarify.

There's no problem with simply connecting to two or more databases as
long as you're only reading them and you have no need for data
consistency between the databases.

However, if you're updating tables in one or more databases or if
updates applied to one database are dependent on the content of other
databases you have a potential problem. You can't guarantee that all
updates are either committed or rolled back without using a transaction
manager to enforce consistency across all the databases.

The downside is that a transaction within the transaction manager will
hold locks in all the databases your transaction accesses until all
databases have successfully committed the transaction. If such a
transaction is long running it can have a major impact on the
performance and response times of the underlying databases.

Note that the consistency issue arising from just connecting to several
databases (i.e. not using a transaction manager) can be a problem for BI
applications despite them being read-only: if one database is updated
while you're retrieving data it could make the data set you're analyzing
inconsistent. Visualize the situation where online stock control is
being used, but supplier and customer accounts are only updated
periodically: there's no way a BI application will get a consistent
snapshot during the day. This the reason many organizations use data
warehouses to support their BI systems. Once data is extracted from the
operational databases and loaded into a data warehouse you know its
consistent and will remain so until the next snapshot is extracted.

HTH

 

[Martin Gregorie]

All J2EE app servers has a built in transaction manager that can
handle multiple XA compliant databases.

Thanks for the information. I've used transaction managers but not app
servers so wasn't certain if they did the transaction management bit.

IOW, if the OP is updating multiple databases in Java, he should only do
it with the aid of an app server.