[Info-vax] Oracle Database vs Oracle/Rdb

[Richard Maher]

On 28/06/2019 9:22 pm, Jan-Erik Söderholm wrote:
> Den 2019-06-28 kl. 15:08, skrev Bob Koehler:
>> In article <qf35cn$1hq7$1 at gioia.aioe.org>, 
>> =?UTF-8?Q?Arne_Vajh=c3=b8j?= <arne at vajhoej.dk> writes:
>>> On 6/27/2019 3:11 PM, Craig A. Berry wrote:
>>>>
>>>> I think databases often use storage-backed global sections or 
>>>> equivalent
>>>> for a lot of their I/O so that the OS is just dealing with whole pages
>>>> that get swapped out to disk using memory management primitives.
>>>
>>> That is probably the most efficient.
>>>
>>> But how do they know if the data are actually written to disk?
>>>
>>
>>     I've used such global sections for inter-process communication many
>>     times.  But I think a DBMS does want to know data are on the disk.
>>     I don't know of any way to force that.  As long as the power stays on
>>     and the OS doesn't crash, it will happen eventually, but I would not
>>     want to buy a DBMS that relies on those.
>>
> 
> What is important is that the transaction journal is written
> with committed transactions. Then you can lose the actual
> database data update since it can (will) be rolled forward from
> the journal when the database restarts.
> 
> Rdb tries to write “dirty” pages (pages in cache that has been
> updated from what is on disk) in batches to optimize the I/O.
> On single node (non-clusered) setups, different user processes
> can transfer pages between local buffers in-memory. In clusters
> the pages still have top go down to disk first and re-read.
> 
> But yes, as others also said, modern storage systems has made
> many of the trimming knobs less important, as long as you do
> not go with the defaults for some simple things such as DB page
> size which are way too low for modern storage systems.

An noteworthy distinction between Rdb and Classic here is that Rdb's I/O 
reducing cache management options are restricted to single-node 
scenarios. Oracle's version of the lock manager allows their 
cache-fusion to transfer large amounts of data inter cluster along with 
the lock value block.

Me? I say converting legacy systems to Oracle from Rdb is not worth it 
but with Oracle now providing total cloud DBA support, I'd put new 
system databases there.