From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Andrew Dunstan <andrew(at)dunslane(dot)net> |
Cc: | Данил Столповских <danil(dot)stolpovskikh(at)gmail(dot)com>, pgsql-hackers(at)postgresql(dot)org, o(dot)tselebrovskiy(at)postgrespro(dot)ru, d(dot)frolov(at)postgrespro(dot)ru |
Subject: | Re: Allow deleting enumerated values from an existing enumerated data type |
Date: | 2023-09-28 18:46:22 |
Message-ID: | 1081742.1695926782@sss.pgh.pa.us |
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Lists: | pgsql-hackers |
Andrew Dunstan <andrew(at)dunslane(dot)net> writes:
> I wonder if we could have a boolean flag in pg_enum, indicating that
> setting an enum to that value was forbidden.
Yeah, but that still offers no coherent solution to the problem of
what happens if there's a table that already contains such a value.
It doesn't seem terribly useful to forbid new entries if you can't
get rid of old ones.
Admittedly, a DISABLE flag would at least offer a chance at a
race-condition-free scan to verify that no such values remain
in tables. But as somebody already mentioned upthread, that
wouldn't guarantee that the value doesn't appear in non-leaf
index pages. So basically you could never get rid of the pg_enum
row, short of a full dump and restore.
We went through all these points years ago when the enum feature
was first developed, as I recall. Nobody thought that the ability
to remove an enum value was worth the amount of complexity it'd
entail.
regards, tom lane
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