I am currently working on migrating SQL Server database to Postgres. I found that there is a provision in Postgres to cluster table based on an index which is similar to clustered indexes in Microsoft SQL Server. However the clustering of table is done only one time as per Postgres documentation. And also it is found that we need to exclusively execute the command 'Cluster' on table periodically if we require for each new update or insert operations on the table.
So, I am thinking about adding a trigger that issues 'CLUSTER' command on that particular table based on an index so that the result would be similar to clustered index in MS SQL.
Can anyone have idea if there are any problems in adding trigger for clustering table for each and every update/insert operation?
Related
I'm working on improving Oracle tables' performances.
The table that I have been working on created with 'monitoring' and 'logging' clause. These two, decreasing performance of query and I need to change monitoring to nomonitoring(without dropping tables).
This is working well:
alter table some_table nologging
But to alter monitoring to nomonitoring I use;
alter table some_table nomonitoring
query executes without any errors but there is no change in table structure.
I've been researching on internet for days and also as I saw here there is no such topic for my specific problem.
Thanks in advance.
The monitoring/nomonitoring options are deprecated and are no longer used in Oracle.
Quote from the Oracle 11.2 manual
Formerly, you enabled DBMS_STATS to automatically gather statistics for a table by specifying the MONITORING keyword in the CREATE (or ALTER) TABLE statement. Starting with Oracle Database 11g, the MONITORING and NOMONITORING keywords have been deprecated and statistics are collected automatically. If you do specify these keywords, they are ignored.
(Emphasis mine)
Is there a way to replicate data(like triggers or jobs) from oracle tables to postgres tables and vice versa(for different set of tables) without using external tools? Just one way replication for both the scenarios.
Just a hint:
You can think of create a DB link from Oracle to Postgres which is called heterogeneous connectivity which makes it possible to select data from Postgres with a select statement in Oracle.
Then use materialized views to schedule and store the results of those selects.
As you don't want to use any external tool otherwise the solution should have been much simpler
for 20 tables I need to replicate data from oracle to postgres. For 40 different tables, I need to replicate from postgres to oracle.
I could imagine the following setup:
For the Oracles tables that need to be accessible from Postgres, simply create foreign tables inside the Postgres server. They appear to be "local" tables in the Postgres server, but the FDW ("foreign data wrapper") will forward any request to the Oracle server. So no replication required. Whether or not this will be fast enough depends on how you access the tables. Some operations (WHERE clause, ORDER BY etc) can be pushed down to the Oracle server, some will be done by the Postgres server after all the rows have been fechted.
For the Postgres tables that need to be replicated to Oracle you could have a similar setup: create a foreign table that points to the target table in Oracle. Then create triggers on the Postgres table that will update the foreign table, thus sending the changes to Oracle.
This could all be managed on the Postgres side.
Am new to hiberante JPA. I am working on oracle to postgres migration and we are not using aws dms service for data migration. We would like to move ahead with Java for copying tables which have more than 1 million records. I have problem for below scenario.
Table A - Oracle
Table B - PostGres
Am extracting records from Oracle using ScrollableResults. Once i have the data from Oracle, i need to loop up a value in postgres database for data from Oracle before performing insert into postgres database.
I thought first #ColumnTransformer will help but it is not helping as i dont know how to reference data from oracle on ColumnTransformer expression.
So finally went ahead with writing normal insert query with values and subquery for lookup. Also set hibernate.jdbc.batch_size to 100.
I executed the program in this way and it took 5 mins for 10k records which i feel is slow.
is there any other solution for this problem to improve the performance.
Thanks for all your help
I found the solution. I solved it by storing postgres lookup table in list object then performing search in lookup table list object before performing insert. Now the speed is good.
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.
I just created a new table on 11gR2 and loaded it with data with no index. After the loading was completed, I created several indexes on the new table including primary constraint.
CREATE TABLE xxxx (col1 varchar2(20), ...., coln varhcar2(10));
INSERT INTO xxxx SELECT * FROM another_table;
ALTER TABLE xxxx ADD CONSTRAINT xxxc PRIMARY KEY(col_list);
CREATE INDEX xxxx_idx1 ON xxxx (col3,col4);
AT this point do I still need to use DBMS_STATS.GATHER_TABLE_STATS(v_owner,'XXXX') to gather table stats?
If yes, why? since Oracle says in docs "Oracle Database now automatically collects statistics during index creation and rebuild".
I don't want to wait for automatic stats gathering over night because I need to report the actual size of the table and its index immediately after the above operations. I think running DBMS_STATS.GATHER_TABLE_STATS may give me a more accurate usage data. I could be wrong though.
Thanks in advance,
In Oracle 11gR2 you still need to gather table statistics. I guess you read documentation for Oracle 12c, which automatically collects the statistics but only for direct path inserts, which is not your case, your insert is conventional. Also if you gather statistics (with default options) for brand new table that hasn't been used for queries no histograms will be generated.
Index statistics are gathered when index is built so it's not needed to gather its statistics explicitly. When you later gather table statistics you should use the DBMS_STATS.GATHER_TABLE_STATS option cascade => false so that index statistics aren't gathered twice.
You can simply check the statistics using
SELECT * FROM ALL_TAB_COL_STATISTICS WHERE TABLE_NAME = 'XXXX';