tail

[dn]

On 25/04/2022 04.21, pjfarley3 at earthlink.net wrote:
>> -----Original Message-----
>> From: dn <PythonList at DancesWithMice.info>
>> Sent: Saturday, April 23, 2022 6:05 PM
>> To: python-list at python.org
>> Subject: Re: tail
>>
> <Snipped> 
>> NB quite a few of IBM's (extensively researched) algorithms which formed utility
>> program[me]s on mainframes, made similar such algorithmic choices, in the
>> pursuit of efficiencies.
> 
> WRT the mentioned IBM utility program[me]s, the non-Posix part of the IBM mainframe file system has always provided record-managed storage since the late 1960's (as opposed to the byte-managed storage of *ix systems) so searching for line endings was (and is) irrelevant and unnecessary in that environment.  That operating system also provides basic "kernel-level" read-backwards API's for the record-managed file system, so there was never any need to build reverse-read into your code for that environment.
> 
> The byte-managed file storage used by the Posix kernel running under the actually-in-charge IBM mainframe operating system is, of course, subject to the same constraints and (in)efficiencies discussed in this thread.


Thanks for the clarification (and @wlfraed's addition).

Apologies if misunderstood. The above comment was about utilities which
would choose between algorithms, based on some rapid, initial,
assessment of the task. It was not about 'tail' utility/ies specifically
- and I don't recall using a 'tail' on mainframes, but...

Thus, the observation that the OP may find that a serial,
read-the-entire-file approach is faster is some situations (relatively
short files). Conversely, with longer files, some sort of 'last chunk'
approach would be superior.
-- 
Regards,
=dn