oracle dblink

Hi,
How dblinks work internally? If there is one dblink and more request at one time then ,is it shared among the requests and requests are queued or mulitple instances are created one for each request?
It would be great If I could find material which says wbout oracle dblink basics, creation , usage and management.

Thanks & Regards
Alok
asharma2Asked:
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asimkovskyConnect With a Mentor Commented:
Actually, a db link is NOT a pipe or a constant direct connection from one database to another. All it does is make the local external TNS connection available to sessions internal to the database. The local database server acts as the client while the remote database acts as a server.  For each connection request, you get a separate connection, just like Oracle clients connecting to an Oracle database.

For detailed information on how to administer db links, you can check the Oracle Administrator's Guide or the Net8 Administrator's Guide.


Andrew
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konektorCommented:
1 db session to your database using dblink = 1 session in remote DB
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asharma2Author Commented:
If we use dblink for any online querying So do you see any performace problem , as for each request it will have to open a new session .I will tell you where I am comig from is...I have a local DB with few load and a remote DB with lot of tables.Remote DB  is providing views to which I can query for my purpose.So I am just comparing options of either opening a JDBC connection directly to remote DB or access that through dblink through jdbc on local DB.

could you please tell me pros and cons of dblink in this regard.

Thanks & Regards
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BajwaConnect With a Mentor Commented:
"If we use dblink for any online querying So do you see any performace problem , as for each request
it will have to open a new session ."

Performance depends upon.

1.  How many queries?  
2.  Big queries or short queries.
3.  Queries are optimized/tuned.
4.  Database/Instance is optimized/tuned.
5.  Hardware (network,machines).


"I will tell you where I am comig from is...I have a local DB with few load and a remote DB with lot of tables.Remote DB  is providing views to which I can query for my
purpose.  So I am just comparing options of either opening a JDBC connection directly to remote DB or
access that through dblink through jdbc on local DB."

Well.. JDBC is more robust (i.e. once coded you do not need to maintain links,etc)., but there is overhead.  If there are few queries I will go for DBlink otherwise JDBC.

DBlink is easy to create.
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asharma2Author Commented:
There can be lot of queries, as it's going to be an enquiry system.There can be 50 simultaneous queries at one time.. though all these are just select statements and there can be any number of queries in a day by a user.
What problems do you perceive when there are more number of queries in dblink?
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MoondancerCommented:
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anand_2000vCommented:
No comment has been added lately, so it's time to clean up this TA.
I will leave a recommendation in the Cleanup topic area that this question is:
points to be split between asimkovsky and Bajwa
Please leave any comments here within the next seven days.

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