Re: POC: Cleaning up orphaned files using undo logs

From: Andres Freund <andres(at)anarazel(dot)de>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Thomas Munro <thomas(dot)munro(at)gmail(dot)com>, Dilip Kumar <dilipbalaut(at)gmail(dot)com>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Dmitry Dolgov <9erthalion6(at)gmail(dot)com>, Kuntal Ghosh <kuntalghosh(dot)2007(at)gmail(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: POC: Cleaning up orphaned files using undo logs
Date: 2019-08-05 16:42:16
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On 2019-08-05 11:25:10 -0400, Robert Haas wrote:
> The obvious thing to do seems to be to have UndoLogControl objects own
> SmgrRelations. That would be something of a novelty, since it looks
> like currently only a Relation ever owns an SMgrRelation, but the smgr
> infrastructure seems to have been set up in a generic way so as to
> permit that sort of thing, so it seems like it should be workable.

Yea, I think that'd be a good step.

I'm not 100% convinced it's quite enough, due to the way the undo smgr
only ever has a single file descriptor open, and that undo log segments
are fairly small, and that there'll often be multiple persistence levels
active at the same time. But the undo fd handling is probably a separate
concern than from who owns the smgr relations.

> I think this kind of design would address your concerns about using
> the unowned list, too, since the UndoLogControl objects would be
> owning the SMgrRelations.


> How does all that sound?

A good move in the right direction, imo.


Andres Freund

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