Re: RX2800 sporadic disk I/O slowdowns

On 10/20/2024 8:28 PM, Lawrence D'Oliveiro wrote:

On Sun, 20 Oct 2024 20:13:50 -0400, Arne Vajhøj wrote:

On 10/20/2024 8:06 PM, Lawrence D'Oliveiro wrote:

On Sun, 20 Oct 2024 19:08:41 -0400, Arne Vajhøj wrote:

Let me try again.
>
DB write to plates & system crash => OK but slow

>
The DB knows how to make this fast. Remember its cache is faster than
any disk controller.

>
This is where the DB is writing to plates.
>
You can add a fourth scenario:
>
DB write to DB cache & system crash => guaranteed problem with
transaction

 Transaction resilience is a standard thing with databases (and journalling
filesystems) going back decades.

Yes.
But they can't do miracles.
To be sure to come up ok after a system crash it is either write to
plates or write to a cache that will survive the system crash (raid
controller cache with battery backup).

Some DBMSes don’t even want to work through filesystems, they would rather
manage the raw storage themselves. This is why POSIX async I/O exists
<https://manpages.debian.org/7/aio.7.en.html>.

Yes. That is to avoid any dangerous OS/filesystem cache (and possible
for better performance).
Arne