Re: MVCC cons

On 8/14/07, RPK <rpk(dot)general(at)gmail(dot)com> wrote:
>
> I want to know whether MVCC has cons also. Is it heavy on resources? How
> PGSQL MVCC relates with SQL Server 2005 new Snapshot Isolation.

Of course it does. There ain't no such thing as a free lunch, after all.

PostgreSQL's mvcc implementation means that a row that gets updated a
lot may have many dead rows in the database, and if you don't run
vacuum often enough, or have enough space allocated in your free space
map, your tables can become bloated.

In a worst case scenario, a highly updated table may get so big that
normal vacuuming cannot salvage it and you would have to either
reindex or perform a vacuum full on it.