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Re: When a hashed pathname is deleted, search PATH

From: Chris Down
Subject: Re: When a hashed pathname is deleted, search PATH
Date: Wed, 19 Mar 2014 20:24:56 +0800
User-agent: Mutt/1.5.23 (2014-03-12)

Linda Walsh writes:
> If this was a reactor control program, that's one thing, but in
> deciding what solution to implement to save some small lookup time or
> throw it away, an 90% solution is probably fine.  It's called a
> heuristic.  AI machines use them.  Thinking people use them.  Why
> should bash be different?

You don't use heuristics when you have access to the underlying
mechanisms, that's an extremely poor way to program, and an extremely
good way to accrue technical debt.

> Fixing it isn't about 0/100% fixed, but a combination of actual cost,
> (measurable impact), user perception, and programmer cost to implement
> something that works for most.
> As you drive up the 'perfection rate' or 'uptime' to another 9 (i.e. 90%
> to 99, or 99 to 99.9%) the costs usually go up exponentially.
> If it costs 1 day to implement an 90% algorithm, a 99% algorithm
> easily be a 1-3 month project depending on how you measure.
> 99.9 could could involve a year or more.

If this has been your experience, then you have been working in
environments which I would suggest are not representative of typical
software development. The time cost involved in maintaining large
systems is not directly related to the suitability for use -- quite the

> If you have a machine that can't do a path lookup in <.1 seconds,
> Then walking a PATH env var to do multiple path lookups is gonna hurt
> that many times more.  If your system is so slow that everything is bad,
> then having hashing turned on at all seems a rather unimportant issue.

Proposing solutions based entirely upon speculation about the
environments of the user base of a program that is shipped with almost
all consumer/server Linux distributions is myopic. To state that such a
situation must also require that the system is generally unsuited for
hashing (as opposed to, for example, just having a particularly high
load at one point in time) is to extrapolate far beyond reasonable
bounds of assumption.

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