[Info-vax] Databases versus RMS

[VAXman- at SendSpamHere.ORG]

In article <jmm94e$atj$1 at Iltempo.Update.UU.SE>, Johnny Billquist <bqt at softjar.se> writes:
>On 2012-04-18 12:51, Dirk Munk wrote:
>> VAXman- @SendSpamHere.ORG wrote:
>>> In article<4f8dc739$0$1688$c3e8da3$50776f34 at news.astraweb.com>, JF
>>> Mezei<jfmezei.spamnot at vaxination.ca> writes:
>>>> {...snip...}
>>>>
>>>>> And, generaly speaking, Rdb is more "safe" then a plain RMS
>>>>> based "database".
>>>>
>>>> An RMS write tends to result in an immediate physical write to disk.
>>>> (unless hidden by a storage array which delays writes).
>>>
>>> That's not true!
>>>
>> Indeed it is not. Cobol for instance has the deferred write option.
>
>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...

Ignoring writeback caching, when the $QIO has completed the data should
be on the disk or, at least, in the hands of a storage controller; what
happens to it from that point on is not a VMS issue per se.  The answer
I posted was directed directly at the comment about RMS and immediately
writing to disk.  There are way too may details in RMS that made that a
completely wrong statement.  MBC, MBF, WBH, process and global buffers,
etc.  I've been dealing with all of this for more than 2 years whilst I
have been working on CDC.  I'm thankful that RMS does do all of this or
it would have been impossible (short of performing extra I/O, both ugly
and a performance issue) to obtain a before image!  

-- 
VAXman- A Bored Certified VMS Kernel Mode Hacker    VAXman(at)TMESIS(dot)ORG

Well I speak to machines with the voice of humanity.