I want to know the difference between TABLE and a TABLESPACE in db2-luw.
The tablespace is where tables gets stored.
It links the physical storage layer (files on disks) and the logical storage layer (tables, indexes).
You can assign each table to a tablespace to control the physical storage layout (for example to put some tables on faster or more redundant disks, or to stripe tables across disks).
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I'm managing a PostgreSQL database server for some users who need to create temporary tables. One user accidentally sent a query with ridiculously many outer joins, and that completely filled the disk up.
PostgreSQL has a temp_file_limit parameter but it seems to me that it is not relevant:
It should be noted that disk space used for explicit temporary tables, as opposed to temporary files used behind-the-scenes in query execution, does not count against this limit.
Is there a way then to put a limit on the size on disk of "explicit" temporary tables? Or limit the row count? What's the best approach to prevent this?
The only way to limit a table's size in PostgreSQL is to put it in a tablespace on a file system of an appropriate size.
Since temporary tables are created in the default tablespace of the database you are connected to, you have to place your database in that size restricted tablespace. To keep your regular tables from being limited in the same way, you'd have to explicitly create them in a different, less limited tablespace. Make sure that your user has no permissions on that less limited tablespace.
This is a rather unappealing solution, so maybe you should rethink your requirement. After all, the user could just as well fill up the disk by inserting the data into a permanent table.
I want to ask if its possible that a situation where the main table is in a different tablespace from the index if it affects performance.
i have a senario where a large table 250GB is in a tablespace and the indexes (3) with an average size of 40GB is in default tablespace. could this be the reason why queries are slow
No, unless one of these tablespaces is on slow storage.
I've been trying postgres with a program that fetches data and puts it into the DB.
Right now the tablespace has filled the available space.
How can I cleanup the db in order to reduce it.
If I delete records, will the disk space be released?
Since I'd want to keep this under control, how can I say to postgres tablespace not to autoextend but to have a specific maximum sze?
Thanks
What is the hierarchy of Database related objects in postgres SQL?
Should it be like, table space must be created at instance level unlike other RDBMS(where we have table space under database).
If so we create the table space at instance level, what is the purpose of database? and what is difference between table space and database on postgres server?
An instance (in PostgreSQL called cluster) is a data directory initialized with initdb with a PostgreSQL server process.
A tablespace is a directory outside the data directory where objects can also be stored. Tablespaces are useful for certain corner cases like distributing I/O or limiting space for a subset of the data.
A database is a container for objects with permissions, organized in schemas.
The difference is that tablespaces are a physical concept, it defines a space where the data are stored, while databases are a logical concept about how data are organized, what they mean, how they are related, who is allowed to access them and so on.
The two concepts are orthogonal.
A database can have tables in several tablespaces, and a tablespace can contain data from several databases.
Database is where you organize all your objects. Tablespace is just storage space for those object.
You can storage your db object in different Tablespace. For example one table is storage in a Tablespace in diskA but another Table use a Tablespace in diskB to improve the performance. Or maybe you need a tablespace for big tables and dont mind use a slow big HDD for those objects.
I am using PostgreSQL and I want to add a new data files to existing tablespace ( like in oracle )
I could not found any description on this on PostgreSQL documentation.
How to do this ?
PotgreSQL works different than Oracle. It has a much simpler concept for data storage. Data blocks, extents and segments don't exist. In the same spirit, a tablespace is not split into multiple data files. You just create the tablespace and PostgreSQL creates the necessary files to store the data.
When creating a tablespace, you can provide a location, where PostgreSQL should store the data:
CREATE TABLESPACE dbspace LOCATION '/data/dbs';
This works similar to bigfile tablespaces in Oracle, where you also don't have to manage data files.