Perhaps you want to use the ctid. You can query it like any other column:
http://www.postgresql.org/docs/9.0/static/ddl-system-columns.html
The ctid is not permanent. An alternative is to create tables with OID values.
From: pgsql-general-owner@xxxxxxxxxxxxxx [mailto:pgsql-general-owner@xxxxxxxxxxxxxx]
On Behalf Of Konstantin Izmailov
Sent: Tuesday, November 30, 2010 9:50 PM
To: pgsql-general@xxxxxxxxxxxxxx
Subject: Does Postgres support bookmarks (tuples ids)?
Dear experts,
I've noticed that commercial databases (e.g. SQLServer) and some open source databases (e.g. Cubrid) support so called "bookmarks".
As far as I understood, a bookmark allows quickly jump to a row for retrieval or modification.
Here is scenario that I'm trying to deal with:
A BI/ETL application is querying the Postgres database. The queries return lots of rows (36 mil), each is about 1KB or larger.
So I'm using DECLARE CURSOR/FETCH to read the rows into a buffer (size is 10000 rows, and I'm freeing memory for oldest rows).
The application may alter or re-read some previously read rows by the row index.
Problem is: if a row is not in the buffer (freed) the application cannot resolve row index into row itself.
I considered using a unique key to located the row, but unfortunately some queries do no allows determining the most unique key.
I'm thinking, is it possible to retrieve/alter row by its index after a Postgres Cursor have read the row?
The application allows a customer to define DB Schema as well as the queries, so my code does not have a prior knowledge about DB and queries.
It is supposed to provide a certain API with functions based on row indexes. The API was initially designed for SQLServer, so the goal is to migrate the application from SQLServer to Postgres.
Would you recommend a solution?
Thank you
Konstantin
