Re: Data Storage Issue (Basic Issue)

Lew <>
Sat, 10 May 2008 10:02:02 -0400
Eric Sosman wrote:

    It might be a good idea to learn more about the
anecdote before drawing too many conclusions ... Just
a few quick observations:

    1) The anecdote does not reveal what was measured. This
       five-to-one difference might have been in latency,
       throughput, capacity, license price, or debugging time.

Transactions per minute in a Java Enterprise application hitting an Oracle
back end. It was a saturation test, so exact boundaries aren't available and
I don't have access to the hard data anyway.

    2) The anecdote does not reveal which configuration had
       the better result on the measured quantity, only that
       a difference existed. The final score may have been
       ten to two, but which team won?

Oracle with its direct disk management vs. Oracle working with the file
system. Direct disk management sped up the database throughput by a factor
that they could tell was above five to one, but not by how much.

    3) The anecdote tells us only that the test was "large-
       scale," but nothing else. A few weeks ago near where
       I live, a "large-scale" test called the Boston Marathon
       demonstrated conclusively that wheelchairs are faster
       than motorcycles (even though the motorcycles had a
       head start, the wheelchairs were first to the finish).

Terabyte-order data, on the order of hundreds of thousands of documents per
hour processed through an enterprise application with relevant data extracted
and stored in the database.

    4) The fact (if we assume its existence) that some database
       performed better without a file system than with one does
       not prove that the file system performs poorly. It might
       well be that the database in question does things dumbly
       and forces the file system to do a lot of needless work.

In this case, no. If you read up on Oracle's direct-disk management it is not
dumb, nor is its file-system interaction. None of the big players are stupid
with file-system access, be they Oracle, DB2, Postgres or whomever. You can
pose it as a theoretical risk, but if you pick a reputable product it won't be
an issue at all in real life. No need to panic.

    I'd suggest that you not dismiss Lew's anecdote, but that
you examine its actual information content before forming firm
opinions about file systems vs. raw devices.

Which is exactly why I presented it as an anecdote. Still, seeing it work
like that even in one case is very indicative, wouldn't you agree?


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