Thanks for the reply Tom. As far as I know, the TID of a row can change over time (e.g. when the row is updated). Isn't it so? If so, it wont solve my problem.
It says here (http://www.postgresql.org/docs/9.0/static/ddl-system-columns.html) that "The OID, or even better a user-defined serial number, should be used to identify logical rows.", so I thought I can use OID. You are right as OIDs are 32-bit ints, so they will wrap-around at some point. The reason why I don't want to use a SERIAL user-column is that I want the process to be transparent to the user. What I want accomplished is the following. I want to trace all accesses (read/update/insert) to rows. If a row was accessed twice, it should appear twice in the trace. Later (offline), I want to analyze the trace to find some patterns, and after deducing some results from the pattern, I should be able to access the original rows in the database. For example, if my pattern-analysis says that row x is "best", I should be able to read x from the DB. Hence, a tuple should uniquely be identifiable (have same ID) in the DB and in the trace. What would you suggest for such a scenario? Thanks for the help. On Thu, Sep 1, 2011 at 10:03 PM, Tom Lane <t...@sss.pgh.pa.us> wrote: > Fazool <fazoolm...@gmail.com> writes: >> I am implementing some functionality into Postgresql, where I want to >> track which row was accessed by a user query. I am implementing the >> functionality inside Postgres, so that there are no changes required >> on client side (e.g. re-writing queries). >> Rows are identified by OIDs, and I have set default_with_oids=true, so >> that all tables are created with OIDs. > > It's a serious, serious error to suppose that OIDs are adequate > identifiers for rows in user tables. > > We use OIDs to identify rows in system catalogs. We can get away with > that, more or less, because (a) system catalogs are not likely to > contain billions of rows, and (b) we place a unique index on OID on > every system catalog that has OIDs. Neither of these statements is > very tenable for user tables. > > You haven't said anything about what it is you actually need to > accomplish here, but can you use TIDs as row identifiers? What's > the required lifetime of the identifiers? > > regards, tom lane > -- Sent via pgsql-hackers mailing list (email@example.com) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers