[Darshan-users] Interpretting Darshan rport
carns at mcs.anl.gov
Wed Sep 9 20:23:45 CDT 2015
Thanks for pointing that out Frederico - that is indeed exactly where
the terminology came from!
On 09/09/2015 05:48 PM, Padua, Federico wrote:
> Hi Richard,
> Hi Shane,
> if I may add something just to give some credits, one of the original definitions and distinctions between consecutive and sequential access appears in the early paper in 1996 titled:
> File-Access Characteristics of Parallel Scientific Workloads,
> also known as Charisma project.
> Probably some work before that had defined it but I don’t know it, that’s the “oldest” I’m aware of...
> The definition is also mentioned here (same project, same authors):
> From what it appears from the Darshan plots, they use this convention as Shean well explained.
>> On 09 Sep 2015, at 13:44, Shane Snyder <ssnyder at mcs.anl.gov> wrote:
>> Hi Richard,
>> Sequential describes I/O accesses that are just at any offset greater than the immediately preceding I/O operation. For instance, say I write 100 bytes at offset 0, then my next access is a read at offset 500 -- that would be a sequential access.
>> Consecutive is more strict in that it requires that the current operation be at the offset immediately following the end of the preceding access's end. An example would be if I write 100 bytes at offset 0, then read at offset 100, instead. So, all consecutive accesses are also sequential but not vice versa.
>> Note that there is no distinction between the types of the 2 operations. If the current operation is a write, we don't care if the previous operation was a read or a write, just the ending offset of it.
>> I should probably mention that we have fixed this graph to be more clear in the new development branch of darshan we are preparing to release, as it has been a source of confusion for a number of people.
>> On 09/09/2015 03:23 PM, Hedges, Richard M. wrote:
>>> In the default report, the fourth plot (labelled ?I/O Pattern”) distinguishes between ”Consecutive” and “Sequential” . Could someone explain the distinction for me?
>>> - Richard
>>> Richard Hedges
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