Is there a way to find the details of the databases accessing our Oracle database using the DB links? Dba_db_links holds the information about the DB links that we have in our database to access other databases, but is there a similar kind of table from where we can find the DB links accessing our database or is that getting recorded some where?
Thanks in Advance.
I agree with Justin, that there's no way to determine an explicit list of all databases that have database links into a given database.
However, it is possible to monitor active database links. You can use the following query to see what sessions are via database links and from which databases:
-- who is querying via dblink?
-- Courtesy of Tom Kyte, via AskTom
-- this script can be used at both ends of the database link
-- to match up which session on the remote database started
-- the local transaction
-- the GTXID will match for those sessions
-- just run the script on both databases
Select /*+ ORDERED */
substr(s.ksusemnm,1,10)||'-'|| substr(s.ksusepid,1,10) "ORIGIN",
substr(g.K2GTITID_ORA,1,35) "GTXID",
substr(s.indx,1,4)||'.'|| substr(s.ksuseser,1,5) "LSESSION" ,
s2.username,
substr(
decode(bitand(ksuseidl,11),
1,'ACTIVE',
0, decode( bitand(ksuseflg,4096) , 0,'INACTIVE','CACHED'),
2,'SNIPED',
3,'SNIPED',
'KILLED'
),1,1
) "S",
substr(w.event,1,10) "WAITING"
from x$k2gte g, x$ktcxb t, x$ksuse s, v$session_wait w, v$session s2
where g.K2GTDXCB =t.ktcxbxba
and g.K2GTDSES=t.ktcxbses
and s.addr=g.K2GTDSES
and w.sid=s.indx
and s2.sid = w.sid;
Hope that helps.
When you create a database link in database A that points at database B, there is no notification sent to database B so there is no data dictionary table in B that will tell you that A has a link to it. As far as B is concerned, database A is simply another client that periodically opens a connection to the database.
Generally, when A wants to create a database link to B, a user will be created in B for this purpose (assuming the database link uses a fixed user rather than the current user) since you don't want the password for this account to expire regularly and you don't want the database link to be broken if a particular human leaves the company and has his or her accounts removed. You can audit connections on B, either for the particular accounts that have been created for database links or across all users, and then look through the audit logs to identify connections that are coming from servers that house other databases.
You might be looking out for this.
Step 1: Check the hash_value of the session in X database.
select sql_hash_value from v$session where sid=&sid;
Step 2: Check the full SQL of the session in X database where the SQL is fired.
select sql_fulltext from v$sql where hash_value=&hash_value;
Step 3: Make a note of all the DB links invloved in the SQL and identify the hosts for those DB links.
select * from dba_db_links where db_link like upper('&db_link');
Step 4: In each host (say only one remote host, pointing to database Y) and database X itself, fire the above query (Tom Kyte's) to gather the session details of sessions coming from remote DBs.
Step 5: In database X, check the SID of interest and its corresponding GTXID. Look for the same GTXID in the remote host Y.
Step 6: Get the session ID from the database Y for this GTXID and check the session waits or other details.
Related
I've been looking for answer to this but I can't seem to find the right answer online and my problem goes like this.
I'm trying to query a set of records from another table which is in an another database installed in a different machine. To make it clearer:
My stored procedure is running on IP: 192.168.XX.X1. I get to retrieve all the information I need in this server but I have another set of information or records that can only be retrieved from IP: 192.168.XX.X2.
I was thinking to achieve something like:
DECLARE
-- given that both queries will only return 1 record
CURSOR IS curSample1
SELECT * FROM Database1.Table1;
colSample curSample1%ROWTYPE;
CURSOR IS curSample2
SELECT * FROM Database2.Table1;
colSample curSample2%ROWTYPE;
vText1 VARCHAR(20);
vText2 VARCHAR(20);
BEGIN
OPEN curSample1;
LOOP
FETCH curSample1 INTO colSample1;
EXIT WHEN curSample1%NOTFOUND;
vText1 := colSample1.Column1;
END LOOP;
CLOSE curSample1;
OPEN curSample2;
LOOP
FETCH curSample2 INTO colSample2;
EXIT WHEN curSample2%NOTFOUND;
vText2 := colSample2.Column2;
END LOOP;
CLOSE curSample2;
dbms_output.put_line(vText1 || ',' || vText2);
END;
Any help you could provide will be much appreciated. Thank you very much.
Note: I'm trying this approach as this is the only way we could possibly do it as of now. Thanks again.
You will have to create a db link between your database 1 and database 2. For creating a database link it is not required to have both databases on the same server. Since in your case the databases are on different server you can start with the following steps.
You need a tns entry (pointing to database 2) in the tnsnames.ora file on your database 1 server. You can check if you have this entry by connecting to SQLPLUS from your database 1 machine to database 2.
sqlplus <username>/<password>#<tnsnames of database2>
If you are able to connect from your database 1 server then you can proceed with the following steps for creating the db link.
CREATE DATABASE LINK <dblink_name> CONNECT TO <username> IDENTIFIED BY <password> USING <tnsnames of database2>
Post this you can test your database link by running the following SQL command.
select * from Table#<dblink_name>;
as i know you cannot query data cross database directly.
1,maybe you can use DBlink or DataSync to let the data which in other database can be query.
2,instead of pl/sql procedure, use other development language to do cross DB process is a good idea(ex independent java program).
3,instead of pl/sql procedure, use Oracle Java Procedure to do this.
I have many procedures for which i am using the same db link and this procedure can be executed at different time or some of the procedure runs at the same time depending on the scheduler job. This procedure used to fetch the data from remote database and insert the data in my local database. As i dont want to left open the db connection after execution of every procedure because it produces the load on the database connection which might impact on query cost and query execution time. Thats why i am using dbms_session to close the database link at the end of each and every procedure.
DBMS_SESSION.CLOSE_DATABASE_LINK
But i dont know whether this results any issue while fetching the data for some of the procedure which executes at the same time. As the dbms session close the db link connection for some of the procedures and at the same time if any of the procedure try to acess the db link and it might not fetch the data or results in any error. Will this situation arises while using
DBMS_SESSION.CLOSE_DATABASE_LINK ?
Following are the ways links could be closed:
A. Only session which opened the database link can close it..
Database link are closed when the session is closed...
select * from dba_DB_LINKS will show database links created
V$DBLINK will lists all open/active database links in your session,..
For an indication on how long the dblink has been open, run:
select t.addr, s.sid, s.username, s.machine, s.status,
(sysdate - to_date(t.start_time, 'MM/DD/YY HH24:MI:SS')) * 24 as hours_active
from v$transaction t, v$session s
where t.addr = s.taddr;
How to know if a transaction is local or distributed?
Check v$global_transaction
B. Using ALTER SESSION or explicitly using command:
alter session close database link <name>;
or use the following package:
dbms_session.close_database_link(<name>);
C. It is also posible to set idle_time limit to user under which connects dblink.
On the server side of dblink (target of dblink) issue:
create profile pidle limit idle_time 5; -- 5 minutes
alter user test profile pidle; -- user under which connects dblink
alter system set resource_limit=true; -- must be set to work idle_time limit
(or add resource_limit=true to init.ora or both)
Please note that even though it looks very similar, it's not a duplicate question with this link:
How to list active / open connections in Oracle?
I'm not asking about the number of sessions, but connections. I'm aware that I can query the v$session view, but I don't know how many connections are being used there. If there is a way to derive from it, please enlighten me.
EDIT:
I'm asking about the physical database connection to the database.
Bit confused with your statement I'm not asking about the number of sessions, but connections.
Conceptually both are same. Every active session will correspond to a underlying active connection to the database.
Now, if you meant to know the max allowed connection limit then Documentation says
Maximum number of connections (system and application) across all
databases in an instance = 2048
To know the allowed session configured to your database, you can query v$parameter view like
SELECT name, value
FROM v$parameter
WHERE name = 'sessions'
If you want to know the Active session at any instance Out of total configured to allow then you can query v$session view using the Status column like
SELECT COUNT(*)
FROM v$session
WHERE STATUS = 'ACTIVE'
You may want to refer this post How to check the maximum number of allowed connections to an Oracle database?
I'm using Oracle SQL Developer version 4.02.15.21.
I need to write a query that accesses multiple databases. All that I'm trying to do is get a list of all the IDs present in "TableX" (There is an instance of Table1 in each of these databases, but with different values) in each database and union all of the results together into one big list.
My problem comes with accessing more than 4 databases -- I get this error: ORA-02020: too many database links in use. I cannot change the INIT.ORA file's open_links maximum limit.
So I've tried dynamically opening/closing these links:
SELECT Local.PUID FROM TableX Local
UNION ALL
----
SELECT Xdb1.PUID FROM TableX#db1 Xdb1;
ALTER SESSION CLOSE DATABASE LINK db1
UNION ALL
----
SELECT Xdb2.PUID FROM TableX#db2 Xdb2;
ALTER SESSION CLOSE DATABASE LINK db2
UNION ALL
----
SELECT Xdb3.PUID FROM TableX#db3 Xdb3;
ALTER SESSION CLOSE DATABASE LINK db3
UNION ALL
----
SELECT Xdb4.PUID FROM TableX#db4 Xdb4;
ALTER SESSION CLOSE DATABASE LINK db4
UNION ALL
----
SELECT Xdb5.PUID FROM TableX#db5 Xdb5;
ALTER SESSION CLOSE DATABASE LINK db5
However this produces 'ORA-02081: database link is not open.' On whichever db is being closed out last.
Can someone please suggest an alternative or adjustment to the above?
Please provide a small sample of your suggestion with syntactically correct SQL if possible.
If you can't change the open_links setting, you cannot have a single query that selects from all the databases you want to query.
If your requirement is to query a large number of databases via database links, it seems highly reasonable to change the open_links setting. If you have one set of people telling you that you need to do X (query data from a large number of tables) and another set of people telling you that you cannot do X, it almost always makes sense to have those two sets of people talk and figure out which imperative wins.
If we can solve the problem without writing a single query, then you have options. You can write a bit of PL/SQL, for example, that selects the data from each table in turn and does something with it. Depending on the number of database links involved, it may make sense to write a loop that generates a dynamic SQL statement for each database link, executes the SQL, and then closes the database link.
If you want need to provide a user with the ability to run a single query that returns all the data, you can write a pipelined table function that implements this sort of loop with dynamic SQL and then let the user query the pipelined table function. This isn't really a single query that fetches the data from all the tables. But it is as close as you're likely to get without modifying the open_links limit.
I have 2 connections with different tables in sqldeveloper.
let's say:
ConnectionA with tables: A,B,C
ConnectionB with tables: D,E,F
Now I want to have a query that looks like this:
select aa.name,dd.id
from A aa,D dd;
How can i do this?
If you want to query objects in two different databases using a single SQL statement, you would need to create a database link between the two databases. A database link is an object that resides in the database and is independent of the query tool. In database A, for example, you could create the database link
CREATE DATABASE LINK to_b
CONNECT TO username IDENTIFIED BY password
USING tns_alias_on_a_pointing_to_b
And then when you connect to A, you could do something like
SELECT aa.name, dd.id
FROM a aa,
d#to_b dd
WHERE aa.some_key = dd.some_key
Apparently TOAD Data Point supports Cross-Connection Queries , see:
http://dev.toadfordataanalyst.com/webhelp/Content/Query_Builder/Create_CrossConnection_Queries.htm
Also Oracle SQL Developer seems to support something similar. (see this blog post: Cross Connection Queries)
I found this helpful and to the point of the OP question for Oracle 11g rel 2 and later: http://www.dba-oracle.com/t_how_create_database_link.htm . Basically, right-click on the connection in the Connections pane in SQL Developer, click Properties, and you get the hostname, port, and service name that you can plug into the "USING" part of the CREATE DATABASE LINK statement. Whether you put in Service Name or SID I assume depends on which you used in your connection. example:
create public database link
mylink
connect to
remote_username
identified by
mypassword
using 'myserver:1521/MYSID';