Disk access with fsync on.

Hi,

I would like to know the disk access mechanism for writing data with
default fsync "on".
I am using libpq client library to insert data to db server.
The insert query is typically done as a transaction with fsync "on"
i.e.:

begin;
insert into <tablename> values<values>;
end;

My query is how does it translate to disk access.
Does each insert writes to disk or to memory segment and a consolidated
write to disk, based on segment full or timeout.

I am using Postgres 7.4.5 on Sun Solaris 8.

Thanks,
-Rajan

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