Re: Vacuum DB in Postgres Vs similar concept in other RDBMS

harpreet(dot)dhaliwal01(at)gmail(dot)com ("Harpreet Dhaliwal") writes:
> I was just wondering if Vacuum Db in postgresql is somehow superior
> to the ones that we have in other RDBMS.

The thing that is more akin to VACUUM, in Oracle's case, is the
rollback segment. In Oracle, Rollback segments are areas in your
database which are used to temporarily save the previous values when
some updates are going on.

In the case of Oracle, if a transaction rolls back, it has to go and
do some work to clean up after the dead transaction.

This is not *exactly* like PostgreSQL's notion of vacuuming, but
that's the nearest equivalent that Oracle has.

The Oracle InnoDB product also has the notion of rollback segments; if
you use InnoDB tables with MySQL, the rollback functionality has much
the same behaviour as Oracle.

Note that in the case of PostgreSQL, the MVCC behaviour (which
requires VACUUMing) has the merit that COMMIT and ROLLBACK both have
near-zero costs; in either case, the cost is merely to mark the
transaction as either committed or failed. Data doesn't have to be
touched at time of COMMIT/ROLLBACK; any costs that need to be paid are
deferred to VACUUM time.
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