Re: [HACKERS] Custom compression methods

On Thu, Oct 8, 2020 at 5:54 PM Tomas Vondra
 wrote:
> And is the oidvector actually needed? If we have the extra catalog,
> can't we track this simply using the regular dependencies? So we'd have
> the attcompression OID of the current compression method, and the
> preserved values would be tracked in pg_depend.

If we go that route, we have to be sure that no such dependencies can
exist for any other reason. Otherwise, there would be confusion about
whether the dependency was there because values of that type were
being preserved in the table, or whether it was for the hypothetical
other reason. Now, admittedly, I can't quite think how that would
happen. For example, if the attribute default expression somehow
embedded a reference to a compression AM, that wouldn't cause this
problem, because the dependency would be on the attribute default
rather than the attribute itself. So maybe it's fine.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
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