PostgreSQL automatically creates indexes for PRIMARY KEY and every UNIQUE constraints of a table. Login to a database in PostgreSQL terminal and type \d table_name. All stored indexes will be visualized. If there is a clustered index then it will also be identified.
- PostgreSQL - Unique Indexes
- Such constraints are implemented with unique indexes in PostgreSQL
- Consequently, the target side of a foreign key is automatically indexed
- Re: Performace comparison of indexes over timestamp fields
- List missing indexes on foreign keys
- Re: When is PostgreSQL 8.3 slated for release
- Converting unique index into primary key
- Difference between PRIMARY KEY index and UNIQUE-NOT NULL index
- Primary keys are auto indexed, but foreign keys are not
- To create a INDEX
Completely copying a postgres table with SQL
Thanks for the reply, that's what I was looking for. I just wasn't sure if there was another compelling advantage to use primary keys instead of a unique index.
The use of indexes to enforce unique constraints could be considered an implementation detail that should not be accessed directly. One should, however, be aware that there's no need to manually create indexes on unique columns; doing so would just duplicate the automatically-created index.
- Feed for question 'Postgres and Indexes on Foreign Keys and Primary Keys'
- I just wasn't sure if there was another compelling advantage to use primary keys instead of a unique index
- How and why to add primary keys to my SQL database table when I already have an index
- Thus, it is not necessary to create an index explicitly for primary key columns
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Currently we have primary keys on tables that have significant amounts of updates performed on them, as a result the primary key indexes are becoming significantly bloated. There are other indexes (read this post here) on the tables that also become bloated as a result of this, but these are automatically rebuild periodically by the application (using the concurrently flag) when read usage is expected to be very low.
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PostgreSQL (https://yamamotonight-m.ru/hack/?patch=1446) automatically creates a unique index (https://yamamotonight-m.ru/content/uploads/files/download/index-on-primary-key-postgresql.zip) when a unique constraint or primary (https://yamamotonight-m.ru/hack/?patch=1325) key is defined for a table. The index covers the columns that make up the primary key or unique constraint (a multicolumn index, if appropriate), and is the mechanism that enforces the constraint.
Yes I am using that option for one of my POstgres 9/1 database and it works well. But its still an issue with Foreign keys, which you need to drop and recreate. Also I use Slony for replication and it uses the primary key to check repl.
So, the benefit is no in size of index (1MB is ~ 0/3% of the index size). But, it makes it possible to include data for columns that can't normally be included, because they lack appropriate access method (btree in my example).
In PostgreSQL, There is no concept like: Table Primary Key means default Cluster Index of that table
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PostgreSQL automatically creates an index (https://yamamotonight-m.ru/hack/?patch=1152) for each unique constraint and primary key constraint to enforce uniqueness. Because this is not always needed, and there are many choices available on how to index, declaration of a foreign key constraint does not automatically create an index on the referencing columns.
Indexes with INCLUDE columns and their support in B-tree This patch introduces INCLUDE clause to index definition. This clausespecifies a list of columns which will be included as a non-key part inthe index. The INCLUDE columns exist solely to allow more queries tobenefit from index-only scans. Also, such columns don't need to haveappropriate operator classes. Expressions are not supported as INCLUDEcolumns since they cannot be used in index-only scans. Index access methods supporting INCLUDE are indicated by amcaninclude flagin IndexAmRoutine. For now, only B-tree indexes support INCLUDE clause. In B-tree indexes INCLUDE columns are truncated from pivot index tuples(tuples located in non-leaf pages and high keys). Therefore, B-tree indexesnow might have variable number of attributes.
DBSync for MS Access & Po synchronizes and converts data from MS Access to PostgreSQL server databases and from PostgreSQL to Access with synchronization. It helps to keep your databases up-to-date when moving to PostgreSQL. Features are data export/import, database synchronization, high-speed synchronization via command line and GUI, built-in scheduler. This data synchronization tool allows you to convert foreign keys, indexes and Primary (https://yamamotonight-m.ru/hack/?patch=7806) keys.
How to Setup Slony Replication Using PgAdmin
Then PostgreSQL has to check if the foreign key constraint is still satisfied. It does so by searching if there are rows in the source table that would become orphaned by the data modification. Without an index (check it out), this requires a sequential scan of the source table.
Copy a table in postgres
Not sure those are relevant here since they're mostly used for full text search, but I also hear that they're good at dealing with duplicate keys. Would either a GIN/GiST index help here?
When an index is declared unique, multiple table rows with equal indexed values are not allowed. Null values are not considered equal. A multicolumn unique index will only reject cases where all indexed columns are equal in multiple rows.
This is required so that there is always a well-defined row to which the foreign key points. The index also comes handy if you want to find the row in the target table that matches a row in the source table.
Is there a performance difference between joining on two indexed tables vs a foreign key
Create Paths on the master to both slaves, and on each slave back to the master. Create the paths under each node on the master, using the connection strings specified in the slon config files. Note that future restructuring of the cluster may require additional paths to be defined.