[Info-vax] Databases versus RMS

[Richard B. Gilbert]

On 4/17/2012 7:48 PM, Arne Vajhøj wrote:
> On 4/17/2012 3:40 PM, JF Mezei wrote:
>> Jan-Erik Soderholm wrote:
>>
>>> One DBMS is not like every other DMBS. I have have had a Rdb database
>>> "break" due to a simple power failure.
>>
>> Are there options which make a database more robust, but many database
>> admins, being too inexperienced, don't think about them ?
>
> Usually the default setup is good enough to lose data.
>
>> or are some
>> database systems, being "free/opensourced" just too easy to get majorly
>> screwed up because of a power failure ?
>
> Opn source and close source database use the same techniques.
>
>> I am moving an RMS/All-in-1 application over to my mac using mysql, PHP
>> and HTML. And it appears one can set up a mysql datbaase without any
>> locking, and some of the indexing seems very primitive (there are
>> different indexing engines).
>
> MySQL has locking.
>
> And its indexing are very standard.
>
> I guess that you are talking about the different database
> engines.
>
> You should go for InnoDB engine.
>
> It is also default in latest MySQL versions.
>
>> I can understand one or two records being corrupt because an update was
>> only half written, but should that prevent the rest of the database
>> from running ?
>
> It should not.
>
>>> 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).
>
> RMS has buffering options as well.
>
>> The reason I am askig is to know whether the "industry" has accepted
>> those risks of hiding physical disks behind storage arrays that may not
>> write right away and behind database engines that not only delay writes
>> and cache stuff on their own, but can also get corrupt because of a
>> power failure.
>
> You can get RAID controllers with huge caches, but those comes
> with battery backup.
>
> So those should be pretty well protected against power
> failure.
>
> Arne
>
>

Just how many hours or minutes are those battery backups going to last?
I'd say ten or fifteen minutes.  If you can't bring up your emergency
generators or get a clean shutdown before the batteries run down. . . .