Laurent,
As your question is not SQL-specific, I am posting my reply to
pgsql-novice instead of pgsql-sql.
> I would like to know some things like :
> How do you calculate the length of a record in a table ?
For an estimate: INT4 = 4 bytes
VARCHAR (30) = 30bytes + 2 bytes = 32bytes
Look in the interactive docs under "data types" for the byte-storage
requirements for other data types. Then do some arithmatic.
> How do you estimate the access time to a data in a table ?
That is dependant on so many factors: Disk storage size, speed and
configuration, your PostgreSQL runtime settings, processor type,
speed, what else is running on the system and its resource usage ...
etc.
> How many records can i insert in this database (before the system
> falls down) ?
See the litany above. It's the same answer. Our current highest
actual reported number of records in any one table is 300 million.
But you'd better have the right hardware and configuration for that.
> If you had to insert a multimedia file (.wav) in this database, would
> you do it or not ?
I would save it as a file and store a link in the database. But not
everyone agrees with me about that.
> And where can i find these information ? (i read FAQ and technotes,
> no
> results...)
If you want direct answers, you will need to hire a consultant. The
online documentation has all of the data you need to figure out the
above on your own, but it takes significant calculation and testing.
To summarize: PostgreSQL is fully configurable. As a result, nobody
can tell the limits of your Postgres database without examining your
actual system and experimenting with Postgres settings.
-Josh Berkus