LOBs & DBLink
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  1. #1
    Join Date
    Oct 2001
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    Question LOBs & DBLink

    Hai.
    Can we use DBLink to access/edit, I mean to SELECT or INSERT a BLOB table in the remote database?

    We are using Oracle9i. If not, then what is the workarund for this problem?


    regards,
    Dileep.

  2. #2
    Join Date
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    No, you can not use BLOBs over database links.

    Workarounds? Perhaps you could make use of snapshots (LOBs can be replicated in snapshots).
    Jurij Modic
    ASCII a stupid question, get a stupid ANSI
    24 hours in a day .... 24 beer in a case .... coincidence?

  3. #3
    Join Date
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    INSERT & SELECT of LOBS are no problem via dblink.

  4. #4
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    Quote Originally Posted by ebrian
    INSERT & SELECT of LOBS are no problem via dblink.
    In 9i? I don't think so. Would you care to demonstrate how would you select LOB columns *directly* from the remote table over database link on 9i?

    In 10gRel2 you can access remote LOBs, but only through OCI, JDBC, and PL/SQL interfaces, not directly with SQL.
    Jurij Modic
    ASCII a stupid question, get a stupid ANSI
    24 hours in a day .... 24 beer in a case .... coincidence?

  5. #5
    Join Date
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    Hai.
    I'm getting confused here. One says SELECT/INSERT is not possible using DBLinks and other says its possible.

    Please let me know which is right?

    regards,
    Dileep Tallam.

  6. #6
    Join Date
    Jan 2001
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    3,131
    Test it,and tell us.
    I remember when this place was cool.

  7. #7
    Join Date
    Oct 2001
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    Doha, Qatar
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    Hai everybody.
    I have tried by creating dblinks on two databases pointing to eachother. I created one table each on each database with same names test1. Please see the following:

    SQL>create user test1 identified by test1;

    SQL>grant connect, resource to test1;

    SQL>alter user test1 default tablespace users;

    SQL>conn test1/test1

    SQL>create sequence photonum;

    SQL>create table photoalbm (photoid number(5), photo blob);

    SQL>create or replace trigger photoid
    before insert on photoalbm
    for each row
    begin
    select photonum.nextval into :new.photoid from dual;
    end;
    /

    SQL>create view v_photoalbm
    as select photoid, dbms_lob.getlength(photo) photo from photoalbm;

    SQL>create database link testlk
    connect to test1 identified by test1
    using 'INTDAG';

    SQL> select photoid, dbms_lob.getlength(photo)
    from photoalbm@testlk;
    select photoid, dbms_lob.getlength(photo)
    *
    ERROR at line 1:
    ORA-22992: cannot use LOB locators selected from remote tables


    Now, I tried using the view instead of table directly.

    SQL> insert into photoalbm
    select * from v_photoalbm@testlk;
    2 select * from v_photoalbm@testlk
    *
    ERROR at line 2:
    ORA-00942: table or view does not exist
    ORA-02063: preceding line from TESTLK


    Again I tried using the table name:

    SQL> insert into photoalbm
    select * from photoalbm@testlk;

    0 rows created.


    Nothing works. I created a view and tried to access the view instead of table according to one of the Asktom post.....

    Please let me know........

    regards,
    Dileep Tallam.

  8. #8
    Join Date
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    Doha, Qatar
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    Hai Jurij Modic,
    Also, You said that there is no way in Oracle9i to SELECT/INSERT BLOBS in remote database using DBLink. Its possible in Oracle10g but through OCI, JDBC and PL/SQL and not using SQL statements. Could you let let me know more about this.

    Ofcourse some one said to use Snapshots, but again they are readonly. I mean we can only SELECT from them and no INSERT/UPDATE is possible if we use SNAPSHOTS. Am I right?


    regards,
    Dileep Tallam.

  9. #9
    Join Date
    Mar 2004
    Location
    DC,USA
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    650
    Its possible over dblink.

    For this you need the Transparent Gateway connection which almost supports all the functionality over db's using dblink. To install this needs separate Oracle license.

    The other way is Generic connectivity which has limitations, still you can do most with an ODBC drivers installed which has capability to support multiple active ODBC cursors.

    On most Oracle server you have the generic connectivity. Check your db what way it connects to remote db. Main restrictions of using Generic connectivity is "BLOB/CLOB data cannot be read through passthrough queries", "cannot involve in 2 phase commit". For further ref: Metalink

    I have a remote database with blob column tables and they populate the local db through triggers, procedures, and ofcourse dblink. I have a licensed TG connection.

    Hope this helps the DBA community.
    "What is past is PROLOGUE"

  10. #10
    Join Date
    Oct 2001
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    Doha, Qatar
    Posts
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    Hai Basan.
    I dont have much information about Transparent Gateways. I know that they are used to connect to other database from Oracle transperantly or so. Is it possible to use Transparent Gateway to connect to Oracle DB from another Oracle DB? I have never seen even while installing the Oracle S/W this option. I only see Transparent Gateways for DB2, MS-SQL Server etc.

    Please let me know more about this.

    Also, How to check whether my database is using Generic Connectivity or not?

    Also, you said that you are able to access LOBS using PL/SQL, TRIGGERS etc using DBLinks. Are you able to use direct SQL also to SELECT data from remote Database using DBLink?


    regards,
    Dileep Tallam.

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