Re: pg11+: pg_ls_*dir LIMIT 1: temporary files .. not closed at end-of-transaction

From: Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr>
To: Justin Pryzby <pryzby(at)telsasoft(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-hackers(at)postgresql(dot)org, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, David Steele <david(at)pgmasters(dot)net>, "Bossart, Nathan" <bossartn(at)amazon(dot)com>, Thomas Munro <thomas(dot)munro(at)gmail(dot)com>
Subject: Re: pg11+: pg_ls_*dir LIMIT 1: temporary files .. not closed at end-of-transaction
Date: 2020-03-30 05:16:17
Message-ID: alpine.DEB.2.21.2003300704430.16227@pseudo
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Hello Justin,

>> Well, the following comment says "ignore anything but regular files",
>> so I'm supposing that that is the behavior that we actually want here
>> and failed to implement correctly. There might be scope for
>> additional directory-reading functions, but I'd think you'd want
>> more information (such as the file type) returned from anything
>> that doesn't act this way.
>
> Maybe pg_stat_file() deserves similar attention ? Right now, it'll fail on a
> broken link. If we changed it to lstat(), then it'd work, but it'd also show
> metadata for the *link* rather than its target.

Yep. I think this traditional answer is the rational answer.

As I wrote about an earlier version of the patch, ISTM that instead of
reinventing, extending, adapting various ls variants (with/without
metadata, which show only files, which shows target of links, which shows
directory, etc.) we would just need *one* postgres "ls" implementation
which would be like "ls -la arg" (returns file type, dates), and then
everything else is a wrapper around that with appropriate filtering that
can be done at the SQL level, like you started with recurse.

It would reduce the amount of C code and I find the SQL-level approach
quite elegant.

--
Fabien.

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