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Subject: Re: pgsql: Add kqueue(2) support to the WaitEventSet API.
From: Mark Dilger <mark.dilger@enterprisedb.com>
In-Reply-To: <18091.1582259407@sss.pgh.pa.us>
Date: Mon, 24 Feb 2020 10:29:51 -0800
Cc: Thomas Munro <thomas.munro@gmail.com>,
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To: Tom Lane <tgl@sss.pgh.pa.us>
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> On Feb 20, 2020, at 8:30 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>=20
> This idea doesn't fix every possible problem.  For instance, if you
> have a plperlu function that wants to open a bunch of files, I don't
> see any easy way to ensure we release VFDs to make that possible.
> But it's sure an improvement on the status quo.

I understand that you were using plperlu just as an example, but it got =
me thinking.  Could we ship a wrapper using perl's tie() mechanism to =
call a new spi function to report when a file handle is opened and when =
it is closed?  Most plperlu functions would not participate, since =
developers will not necessarily know to use the wrapper, but at least =
they could learn about the wrapper and use it as a work-around if this =
becomes a problem for them.  Perhaps the same spi function could be used =
by other procedural languages.

I can't see this solution working unless the backend can cleanup =
properly under exceptional conditions, and decrement the counter of used =
file handles appropriately.  But that's the same requirement that =
postgres_fdw would also have, right?  Would the same mechanism work for =
both?

I imagine something like <PgPerluSafe>::IO::File and =
<PgPerluSafe>::File::Temp which could be thin wrappers around IO::File =
and File::Temp that automatically do the tie()ing for you. (Replace =
<PgPerluSafe> with whichever name seems best.)

Is this too convoluted to be worth the bother?

=E2=80=94
Mark Dilger
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company