I would like to create a cached copy of a table via dblink in oracle. The story is the following:
I have two tables (employee, work) which are joined via a third table (emloyee_work) in a remote database. The reason for that is to decouple the connection between the two entities so that they are not able to be connected directly.
To handle the data easily we have a view that connects the tables via the join table. One can argue that this is the same as having the join table in the same database as the other two but that in not the point right now.
On a new site, the db link latency is very high which causes a major drop in performance since for every select the view is built and a select is executed for each employee through the db link.
The structure has relative high read count and low write count.
The question is whether there is a possibility to "mirror" or copy the remote join table to the local database? This copy should be temporary and should not be persisted.
This way the view would be executed on the local copy.
EDIT: Oracle version is 11gR2
You could use refreshed on demand materialized views.
See also this link where they talk about implementing a materialized view over a dblink.
Since you are using Oracle 11g, you may create an ad-hoc, RAM-based Materialized View.
Related
I want to ask you if there is a solution to auto-synchronize a table ,e.g., every one minute based on view created in oracle.
This view is using data from another table. I've created a trigger but I noticed a big slowness in database whenever a user update a column or insert a row.
Furthermore, I've tested to create a job schedule on the specified table (Which I wanted to be synchronized with the view), however we don't have the privilege to do this.
Is there any other way to keep data updated between the table and the view ?
PS : I'm using toad for oracle V 12.9.0.71
A materialized view in Oracle is a database object that contains the results of a query. They are local copies of data located remotely, or are used to create summary tables based on aggregations of a table's data. Materialized views, which store data based on remote tables, are also known as snapshots.
Example:
SQL> CREATE MATERIALIZED VIEW mv_emp_pk
REFRESH FAST START WITH SYSDATE
NEXT SYSDATE + 1/48
WITH PRIMARY KEY
AS SELECT * FROM emp#remote_db;
You can use cronjob or dbms_jobs to schedule a snapshot.
I have the following scenario and need to solve it in ORACLE:
Table A is on a DB-server
Table B is on a different server
Table A will be populated with data.
Whenever something is inserted to Table A, i want to copy it to Table B.
Table B nearly has similar columns, but sometimes I just want to get
the content from 2 columns from tableA and concatenate it and save it to
Table B.
I am not very familiar with ORACLE, but after researching on GOOGLE
some say that you can do it with TRIGGERS or VIEWS, how would you do it?
So in general, there is a table which will be populated and its content
should be copien to a different table.
This is the solution I came up so far
create public database link
other_db
connect to
user
identified by
pw
using 'tns-entry';
CREATE TRIGGER modify_remote_my_table
AFTER INSERT ON my_table
BEGIN INSERT INTO ....?
END;
/
How can I select the latest row that was inserted?
If the databases of these two tables are in two different servers, then you will need a database link (db-link) to be created in Table A schema so that it can access(read/write) the Table B data using db-link.
Step 1: Create a database link in Table A server db pointing to Table B server DB
Step 2: Create a trigger for Table A, which helps in inserting data to the table B using database link. You can customize ( concatenate the values) inside the trigger before inserting it into table B.
This link should help you
http://searchoracle.techtarget.com/tip/How-to-create-a-database-link-in-Oracle
Yes you can do this with triggers. But there may be a few disadvantages.
What if database B is not available? -> Exception handling in you trigger.
What if database B was not available for 2h? You inserted data into database A which is now missing in database B. -> Do crazy things with temporarily inserting it into a cache table in database A.
Performance. Well, the performance for inserting a lot of data will be ugly. Each time you insert data, Oracle will start the PL/SQL engine to insert the data into the remote database.
Maybe you could think about using MViews (Materialized Views) to replicate the data via database link. Later you can build your queries so that they access tables from database B and add the required data from database A by joining the MViews.
You can also use fast refresh to replicate the data (almost) realtime.
From perspective of an Oracle Database Admin this would make a lot more sense than the trigger approach.
try this code
database links are considered rather insecure and oracle own options are having licences associated these days, some of the other options are deprecated as well.
https://gist.github.com/anonymous/e3051239ba401e416565cdd912e0de8c
uses ora_rowscn to sync tables across two different oracle databases.
We have a legacy app that I am rewriting in .net. All of our databases are oracle and make use of database links. Is there any way for Entity Framework 6 to generate models based on tables located on a different database?
Currently the legacy app gets data from table like this
SELECT * FROM emp#foo2;
where its db connection is to database foo that has a database link to the database foo2.
I would like to reproduce this using EF6. So far all I have found regarding this is this question.
You can do two things that EF 4 or higher will work with:
CREATE VIEW EMP as SELECT * FROM emp#foo2;
CREATE MATERIALIZED VIEW EMP as SELECT * FROM emp#foo2;
LOBS are not accessible across a database link without some contorted PL/SQL processing to read the LOB piece by piece.
I believe fast refresh does not work across database links so you must consider the size of the table on the linked database. If you are refreshing a million rows you may find the time to do this is an issue. Most large tables are full of tombstone data that never changes so a timestamp column with the last modified date could help you create a package that only picks out the changed data.
If you are doing complicated joins for either ensure that Oracle considers the column that would be the primary key as not null.
You can add a primary key on views and materialized view but it must be disabled. See here for details.
I have a question: I have a table (say tableA) in a database (say dbA) and I need to mirror tableA as another table (say tableB) in another database (say dbB).
I know this can be done via (materialised) view or via informatica. But by problem is that I need to sync DDL as well. For example if a column is added in tableA, the column should automatically reflect in tableB.
Can this be done anyway directly via oracle or Informatica.
(or I will have to write a procedure to sync table on basis of all_tab_cols).
Yes, you could:
create another database as a logical standby database with Data Guard
use Oracle Streams
I would use (2) if you just need a single table in the other database or (1) if you need an entire schema (or more).
Good afternoon,
I have 3 databases; the SIDs are config, prod1 and prod2.
I am using Materialized Views to replicate data on 11 tables in the config database onto the other two databases. The Materialized Views are currently refreshing every five seconds but it would be ideal if they were updated on commit.
I came across this website that explains that when replicating from a remote database that on commit is not supported.
This is what I was expecting to work
CREATE MATERIALIZED VIEW "schema"."table" USING INDEX REFRESH FORCE ON COMMIT AS select column1 from schema.table#config;
The method "refresh fast on demand with primary key" is suggested in the link but obviously this is on demand. I am wondering what ideas anyone may have in order to get a refresh-on-commit environment running if possible?
Thanks
You can't create a materialized view refreshed on commit from a remote table. From the documentation:
Restrictions on Refreshing ON COMMIT
This clause is not supported for materialized views containing object types or Oracle-supplied types.
This clause is not supported for materialized views with remote tables.
The reason is that the database link is defined in the "child" database, not in the "parent" database. Therefore, the parent database can't possibly trigger or modify anything in the child database on its own.
If you want a 100% real-time copy of a table, I suggest a view.
If you want to replicate the data on commit, you could modify your DML procedures so that they update the children remote tables at the same time.