Re: Database writing architecture

pablo_at_mew.corp.sgi.com (Pablo Sanchez) wrote:
>
>In article <316D6BD4.41C67EA6_at_exu.ericsson.se>, Gerald Ward <exuward_at_exu.ericsson.se> writes:
>
>We had a guy named Francisco Casas who used to post here and he made
>the claim that *any* DBMS must use raw partitions if you want
>integrity.

I have great respect for Francisco Casas but I have to disagree with this alleged claim of his. A DBMS can use filesystems and preserve data integrity if it uses the *write-through mode* in writes. Both Unix and NT support the write-through mode in writes. But this approach has its drawbacks:

(1) In Unix, the write with write-through is synchronous. It is

    actually called "synchronous write" in Unix. This can create     io blocking situations for multithreaded DBMS and slow down     performance considerably.

(2) Large files have to use indirect pointers to reach most actual

    data blocks. This indirect access can slow down performance     when the file size is large (say, GB and up.)

Filesystem-based database used to have the advantage of being able to do large block io. But now Sybase 11 lets you do large block io (up to 16k) on raw devices. So whether that old performance advantage of file over raw device still exists or not is unclear.

Paul Chen, Ph.D.
Surfing the net from home.
Disclaimer: My opinions only! Received on Sat Apr 13 1996 - 00:00:00 CEST