I have a Mysql server(node A) in galera cluster 1 and a Mysql server (node B) in galera cluster 2.
Node A and node B are indifferent cluster so they have completely different write nodes.
I'm trying to join tables in node A with those tables in node B use FederatedX engine.
But found these words in MariaDB's Knowledge Base about the FederatedX's limitations.
There is no way for the handler to know if the foreign database or table has changed. The reason for this is that this database has to work like a data file that would never be written to by anything other than the database. The integrity of the data in the local table could be breached if there was any change to the foreign database.
These nodes are in different clusters,so it must be update by other write nodes.
But I need to figure out the way to join Tables in different nodes.
Some website says that federated tables will use remote server's data.
It sounds like that I don't have to worry about it... But I'mnot quite sure.
So...my question is...Does Federated tables in different clusters will work?
Thanks a lot.
Related
I have a database D1 on the cluster C1 and I have a bunch of (maybe 100) principals defined on D1. Now assume that I also have another database D2 on the cluster C2. Also I am admin on both the databases. Is there any way I can just script out all my service principals and execute that script in one shot against D2 and thus achieve migration of all the principals? If not, is there any other way of achieving this, other than explicitly granting permission to each one of the principals against the database D2? (that will be like executing a hundred commands)
There's no current way of exporting/importing database-level principals from one database to another.
One option for you to consider is writing a simple app/script (using Kusto's API) that:
Lists all principals using .show database ['database_name'] principals
Generates a list of .add database ['database_name'] <role> (<principal>) commands based on 1. (or a single command per role, were is a comma-separated list of principals)
Runs all commands from 2.
I have a specific architecture to set up with postgresql.
I have a system that is based on two databases N and N+1.
The database N is available for clients in read only mode, and the database N+1 is available for modification for clients.
The client can also send two commands to the system:
An "apply" command: all the modifications made on the N+1 db are kept and the new state of the system is a readonly db with N+1 data and a N+2 db with same data available for writes.
A "reset" command: the N+1 db is dropped and a new copy of the N database is made for writes access for the users.
My first idea was to keep two databases in an instance of postgresql and perform pg_dump and pg_restore command on apply or reset command, and rename the database for the apply(N+1 -> N). The db can possibly reach the size of 8 Go, so I am currently performing test of such dump&restore on a Centos 6.7 vm.
Then I looked to the pg_basebackup command, to set up a hot standby database that will be the readonly one. The problem is that such an architecture is based on the idea of data replication from a master to a slave, and that is something I don't want since the client can ask a reset command that will drop the N+1 db.
The thing is I don't know if a system based on daily dump/restore is viable or not, or if there is with postgresql a simple way to handle two databases with the same schema and "detect and apply" the differences between the two: with that ability, I will be able , on apply command, to copy from N+1 to N only the difference, and the contrary with a reset command.
Any idea ?
I have two postgresql databases, one on my local machine and one on a remote machine. If I'm connected to the local database (with psql), how do I execute a statement that inserts rows into a table on the remote database by selecting rows from a table on the local database? (I've seen this asked a handful of times, like here, here and here, but I haven't yet found a satisfactory answer or anyone saying definitively that it's not possible).
Specifically, assume I have tables remotetable and localtable, each with a single column columnA. I can run this statement successfully:
select dblink_exec('myconnection', 'insert into remotetable (columnA) values (1);');
but what I want to do is this:
select dblink_exec('myconnection', 'insert into remotetable (columnA) select columnA from localtable;');
But this fails with: relation "localtable" does not exist, presumably because localtable does not exist on the remote database.
Is it possible to do what I'm trying to do? If so, how do I indicate that localtable is, in fact, local? All of the examples I've seen for dblink-exec show inserts with static values, not with the results of a local query.
Note: I know how to query data from a remote table and insert into a local table, but I'm trying to move data in the other direction.
If so, how do I indicate that localtable is, in fact, local?
It's not possible because dblink acts as an SQL client to the remote server. That's why the queries sent through dblink_exec must be self-contained: they can do no more than any other query sent by any SQL application. Every object in the query is local to it from the server's perspective.
That is, unless you use another functionality, a Foreign-Data Wrapper with the postgres_fdw driver. This is a more sophisticated way to achieve server-to-server querying in which the SQL engine itself has this notion of foreign and local tables.
According to one of my posts (below) it seems that there is no such thing as a database in Oracle. What we call database in MySQL and MS-SQL is called schema in Oracle.
If that is the case, then why do the oracle docs mention the create database statement ?
For the record, I am using Oracle 11g and oracle SQL Developer GUI tool.
Post-
How to create a small and simple database using Oracle 11 g and SQL Developer?
The create database statement from oracle docs is given below. If there is no database concept, then how did this command come into the picture ?
CREATE DATABASE
CREATE DATABASE [ database ]
{ USER SYS IDENTIFIED BY password
| USER SYSTEM IDENTIFIED BY password
| CONTROLFILE REUSE
| MAXDATAFILES integer
| MAXINSTANCES integer
| CHARACTER SET charset
| NATIONAL CHARACTER SET charset
| SET DEFAULT
{ BIGFILE | SMALLFILE } TABLESPACE
| database_logging_clauses
| tablespace_clauses
| set_time_zone_clause
}... ;
There is concept of a "database" in Oracle. What the term "database" means in Oracle terms is different than what the term means in MySQL or SQL Server.
Since you are using the express edition, Oracle automatically runs the CREATE DATABASE statement as part of the installation process. You can only have 1 express edition database on a single machine. If you are installing a different edition, you can choose whether to have the installer create a database as part of the installation process or whether to do that manually via the CREATE DATABASE statement later. If you are just learning Oracle, you're much better off letting Oracle create the database for you at installation time-- you can only create the database via command-line tools (not SQL Developer) and it is rare that someone just starting out would need to tweak the database settings in a way that the installer didn't prmopt you for.
In Oracle, a "database" is a set of data files that includes the data files for the SYS and SYSTEM schemas which contain all the Oracle data dictionary tables, the data files for the TEMP tablespace where sorts and other temporary operations occur, and the data files for whatever schemas you want to create. In SQL Server and other RDBMSs, these would be separate "databases". In SQL Server, you have a master database, a tempdb database, additional database for different products (i.e. msdb for the SQL Server Agent), and then additional user-defined databases. In Oracle, these would all be separate schemas in a larger container that Oracle refers to as a "database".
Occasionally, a DBA will want to run multiple Oracle databases on the same server-- most commonly when there are different packaged applications that have different requirements about database versions or parameters. If you want to run application A that requires an 11.2 database and application B that doesn't support 11.2 yet, you would need to have two different databases on the server. The DBA could create a separate database and a separate instance but that doubles the memory requirements, doubles the number of background processes required to run the database, and generally makes things less scalable. It's necessary if you really want to run different versions of the database simultaneously but it's not ideal.
The person who answered your original question is correct. The DDL (Data Definition Language) above prepares a space for schemas, which is analogous to MySQL's 'database'. The above statement defines characteristics of the schemas, such as timezone, MBs of space for tables, encoding characterset, root account, etc. You would then issue DDL statements such as those in your other post to create schemas, which define what each user can see.
Hi:
In our new application we have to use the oracle as the db,and we use mysql/sqlserver before,when I come to oracle I am confused by its concepts,for exmaple,the table space,the object,the schema table,index, procedure, database link,...:(
And the schema is closed to the user,I can not make it.
Since when we use the mysql,I just know that one database contain as many tables,and contain as many users,user have different authentication for different table.
But in oracle,everything is different.
Anyone can tell me some basic concepts of oracle,and some quick start docs?
Oracle has specific meanings for commonly-used terms, and you're right, it is confusing. I'll build a hierarchy of terms from the bottom up:
Database - In Oracle, the database is the collection of files that make up your overall collection of data. To get a handle on what Oracle means, picture the database management system (dbms) in a non-running state. All those files are your "database."
Instance - When you start the Oracle software, all those files become active, things get loaded into memory, and there's an entity to which you can connect. Many people would use the term "database" to describe a running dbms, but, once everything is up-and-running, Oracle calls it an, "instance."
Tablespace - A abstraction that allows you to think about a chunk of storage without worrying about the physical details. When you create a user, you ask Oracle to put that user's data in a specific tablespace. Oracle manages storage via the tablespace metaphor.
Data file - The physical files that actually store the data. Data files are grouped into tablespaces. If you use all the storage you have allocated to a user, or group of users, you add data files (or make the existing files bigger) to the tablespace they're configured to use.
User - An abstraction that encapsulates the privileges, authentication information, and default storage areas for an account that can log on to an Oracle instance.
Schema - The tables, indices, constraints, triggers, etc. that are owned by a particular user. There is a one-to-one correspondence between users and schemas. The schema has the same name as the user. The difference between the two is that the user concept is all about account information, while the schema concept deals with logical database objects.
This is a very simplified list of terms. There are different states of "running" for an Oracle instance, for example, and it's easy to get into very nuanced discussions of what things mean. Here's a practical exercise that will let you put your hands on these things, and will make the distinctions clearer:
Start an already-created Oracle instance. This step will transform a group of files, or as Oracle would say, a database, into a running Oracle instance.
Create a tablespace with the CREATE TABLESPACE command. You'll have to specify some data files to put into the tablespace, as well as some storage parameters.
Create a user with the CREATE USER command. You'll see that the items you have to specify have to do with passwords, privileges, quotas, and the like. Specify that the user's data be stored in the tablespace you created in step 2.
Connect to the Oracle using the credentials you created with the new user from step 3. Type, "SELECT * FROM CAT". Nothing should come back yet. Your user has a schema, but it's empty.
Run a CREATE TABLE command. INSERT some data into the table. The schema now contains some objects.
table spaces: these are basically
storage definitions. when defining a
table or index, etc., you can specify
storage options simply by putting
your table in a specific table_space
table, index, procedure: these are pretty much the same
user, schema: explained well before
database link: you can join table A in instance A and table B in instance B using a - database link between the two instances (while logged in on of them)
object: has properties (like a columns in a table) and methods that operate on those poperties (pretty much like in OO design); these are not widely used
A few links:
Start page for 11g rel 2 docs http://www.oracle.com/pls/db112/homepage
Database concepts, Table of contents http://download.oracle.com/docs/cd/E11882_01/server.112/e16508/toc.htm