[Info-vax] RX2800 sporadic disk I/O slowdowns

[Arne Vajhøj]

On 10/21/2024 8:35 AM, Simon Clubley wrote:
> On 2024-10-19, Lawrence D'Oliveiro <ldo at nz.invalid> wrote:
>> On Sat, 19 Oct 2024 21:52:16 -0400, Arne Vajhøj wrote:
>>> The context is one where data loss is not acceptable.
>>
>> Data loss is unavoidable. If the power goes out, all computations in
>> progress get lost. There?s no way around that.
> 
> Bollocks. It's called checkpointing and restart points for compute
> based operations. It's called transaction recovery for I/O based
> operations.

I read his comments as being about what happens between
checkpoints/commits.

It is not possible to recover that. But it is not
desirable to recover that, because that would be
an inconsistent state.

begin
update accounts set amount = amount - ? where id = ?
 >>>> here <<<<
update accounts set amount = amount + ? where id = ?
commit

or:

checkpoint m
m.accounts[id_a] -= xframt
 >>>> here <<<<
m.accounts[id_b] += xframt
checkpoint m

is really the same.

Arne