I use postgresql. I have many databases in a server. There is one database which I use the most say 'main'. This 'main' has many tables inside it. And also other databases have many tables inside them.
What I want to do is, whenever a new row is inserted into 'main.users' table I wish to insert the same data into 'users' table of other databases. How shall I do it in postgresql? Similarly I wish to do the same for all actions like UPDATE, DELETE etc.,
I had gone through the "logical replication" concept as suggested by you. In my case I know the source db name up front and I will come to know the target db name as part of the query. So it is going to be dynamic.
How to achieve this? is there any db concept available in postgresql? Or I welcome all other possible ways as well. Please share me some idea on this.
If this is all on the same Postgres instance (aka "cluster"), then I would recommend to use a foreign table to access the tables from the "main" database in the other databases.
Those foreign tables look like "local" tables inside each database, but access the original data in the source database directly, so there is no need to synchronize anything.
Upgrade to a recent PostgreSQL release and use logical replication.
Add a trigger on the table in the master database that uses dblink to access and write the other databases.
Be sure to consider what should be done if the row alreasdy exists remotely, or if the rome server is unreachable.
Also not that updates propogated usign dblink are not rolled back if the inboking transaction is rolled back
Related
I'm using the Oracle foreign data wrapper and would like to have local copies of some of my foreign tables locally. Is there another option than having materialized views and refreshing them manually?
Not really, unless you want to add functionality in Oracle:
If you add a trigger on the Oracle table that records all data modifications in another table, you could define a foreign table on that table. Then you can regularly run a function in PostgreSQL that takes the changes since you checked last time and applies them to a PostgreSQL table.
If you understand how “materialized view logs” work in Oracle (I don't, and I think the documentation doesn't tell), you could define a foreign table on that and use it like above. That might be cheaper.
Both of these ideas would still require you to regularly run something in PostgreSQL, but you might be cheaper. Perhaps (if you have the money) you could use Oracle Heterogenous Services to modify a PostgreSQL table whenever something changes in an Oracle table.
i would like to import all data of a existing table of one database to a new table present inside different database in postgres, any suggestions will be helpful.
The easiest way would be to pg_dump the table and pg_restore in the target database.
In case it is not an option, you should definitely take a look a postgres_fdw (Foreign Data Wrapper), which allows you to access data from different databases - even from different machines. It is slightly more complex than the traditional export/import approach, but it creates a direct connection to the foreign table.
Take a look at this example.
I have a large postgresql database, and I want to track all it's tables if a change has been made.
The reason for that is that I can't know a relation between two different tables in the database.
I googled about it but I couldn't find anything helpful.
So how can I know if a change has been made to a table ?
There isn't currently a global audit function in PostgreSQL.
It'll be possible to build one using the new logical changeset extraction feature in 9.4, and I know some people are working on that.
In the mean time, you need to add some form of audit trigger to every table.
I am new to the PostgreSQL database. What my visual c++ application needs to do is to create multiple tables and add/retrieve data from them.
Each session of my application should create a new and distinct database. I can use the current date and time for a unique database name.
There should also be an option to delete all the databases.
I have worked out how to connect to a database, create tables, and add data to tables. I am not sure how to make a new database for each run or how to retrieve number and name of databases if user want to clear all databases.
Please help.
See the libpq examples in the documentation. The example program shows you how to list databases, and in general how to execute commands against the database. The example code there is trivial to adapt to creating and dropping databases.
Creating a database is a simple CREATE DATABASE SQL statement, same as any other libpq operation. You must connect to a temporary database (usually template1) to issue the CREATE DATABASE, then disconnect and make a new connection to the database you just created.
Rather than creating new databases, consider creating new schema instead. Much less hassle, since all you need to do is change the search_path or prefix your table references, you don't have to disconnect and reconnect to change schemas. See the documentation on schemas.
I question the wisdom of your design, though. It is rarely a good idea for applications to be creating and dropping databases (or tables, except temporary tables) as a normal part of their operation. Maybe if you elaborated on why you want to do this, we can come up with solutions that may be easier and/or perform better than your current approach.
I have a report in SQL server and I am migrating this to Oracle.
The approach I used in SQL server is load sum(sales) , person for given month into temporary tables (hash tables) and use this table to join with other transaction tables show the details, but when it comes to oracle I am not sure if I can use the same method here, because hash tables (temporary tables in SQL server) are specific to session and might not create any problem with output, please advise if there is anything in oracle which is analogous to that.
I came to know there are global temp tables in oracle, do they work in the manner I mentinoed above, also
If a user has no create/drop table privileges can they still use gloabal temp tables?
please help me.
You'll have to show some code or atleast some pseudo-code of how your process runs for anyone to help you. Having said that...
One thing that is different in oracle compared to temporary tables in other databases is that you do not create them each time you need them. You create them once and the data in the table is present either until you commit/rollback (transaction based) or until you end your session (session-based global temporary tables). Also, The data in a temporary table is visible only to the session that inserts the data into the table..
If you are generating the output files once and you don't need that data later, then Global temporary tables would probably fit in cleanly, with some minor changes.
Since you do not create the temporary tables each time you use them, you don't need the create/drop privilege. All you'd need is the insert/read privilege. Just read will not help because you cannot read another session's data anyways, so there is no use for it.