On 07/30/1999 09:34 -0700, Roeland M.J. Meyer wrote:
>> > Actually, it might be useful to consider several different
>> > cases (you mentioned
>> > 1 and 4, but there are a couple other common cases):
>> > 1) RDBMS raw block device usage
>> > 2) small-file file system (i.e. news server)
>> > 3) large-file file system (i.e. images, archives, data
>> > warehousing, ftp servers)
>> > 4) general purpose file system (somewhere between 2 and 3)
>> >
>>
>> Data warehousing is the RDBMS case, usually done with exactly the same
>> hardware and software, but different optimizations. The schemas are, of
>> course much different (star queries are a PITA!). Much of it depends on
>> how the RDBMS is implemented. However, I don't think anyone does RAW
Don't know about under Linux, but I know of a number of sites still using
raw for databases (granted, I don't think any of them are on Oracle, they're
all either Sybase or Informix).
>> anymore. Image archives, for anyone doing a production implementation,
>> isuslaly served up as BLOBs, under an RDBMS (back to the RDBMS case).
I wasn't thinking of images only in the graphical sense - we've got a server
where we keep large images of databases (kind of a fast rollback/recovery
solution - don't ask).
>> This gives us case 1 and 2 as special/rare-use cases and drops RDBMS and
>> FTP servers into case 3.
>>
>> What do you think?
Another way of looking at it is:
1) constant (or near constant, anyway) medium IO block size mostly
sequential access (corresponds to 1 above)
2) small random access (corresponds to 2 above)
3) large sequential access (3 above)
4) random size random access (4 above)
I guess I might concur that 1 may have features in common with any of 2-4,
depending on what exactly the DBMS is doing - small vs large tables,
small vs large updates, etc. Where 1 tends to be different, is in the
fact that the kernel buffer cache is usually bypassed in this case, so
the characteristic I/O patterns may be significantly different because
of the use of different caching and write gathering algorithms. I don't
know if there's a big enough difference to worry about, but I don't know
there isn't either. That's why I always recommend benchmarking several
different configs.
I still think 2-4 are sufficiently different, though - 2 and 3 are very
optimized for particular purposes, and 4 is less optimized, just designed
so that everything works as well as can be expected.
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