[Info-vax] Databases versus RMS

[Jan-Erik Soderholm]

Johnny Billquist wrote 2012-04-18 19:53:
> On 2012-04-18 15:43, Bob Koehler wrote:
>> In article<jmm94e$atj$1 at Iltempo.Update.UU.SE>, Johnny
>> Billquist<bqt at softjar.se> writes:
>>>
>>> Even beyond any language issue, or RMS details, the OS can cache and
>>> defer actual writes to the disk without you ever knowing about it. Not
>>> to mention that disks also cache things...
>>>
>>
>> OS cache? Are you dreaming UNIX? VMS has never cahced any data I
>> cared about without my explicitly telling it to do so.
>
> Really? I find it hard to believe. RSX have done caching of things from the
> disk at that low level since day one. F11ACP do some caching for the
> system, keeping the most recently referenced directories around in a cache
> in the ACP.
>
> Newer versions of RSX also do caching of individual blocks fully
> transparent at the OS level. It's selectable if you want writes to be
> write-back or write-through.
>
> That VMS would have none of this sounds unlikely, as well as very bad for
> performance.
>
>> Disks that cache should use a non-volatile memory to do so, or
>> contain internal power storage sufficient to flush the cache.
>
> Right. But that is still a cache that can cause surprising results,
> although I freely admit that the caches in the disks are normally very
> reliable.
>
> Johnny
>

You are mixing read and write cache. Make sure you are talking
about the same thing before arguing... :-)