[Info-vax] Databases versus RMS

[Dirk Munk]

Richard B. Gilbert wrote:
> 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. . . .
>

Many hours, sometimes even a few days. Usually the disks are not powered 
by the batteries, only the RAM memory of the cache.