From: Tom Lane <tgl@sss.pgh.pa.us>
To: Vitaly Ustinov <vitaly@ustinov.ca>
Cc: Peter Eisentraut <peter.eisentraut@enterprisedb.com>
Cc: pgsql-bugs@lists.postgresql.org, "David G. Johnston" <david.g.johnston@gmail.com>
Subject: Re: Generated column is not updated (Postgres 13)
Date: Thu, 20 May 2021 17:09:08 -0400
Message-ID: <3795805.1621544948@sss.pgh.pa.us> (raw)
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Vitaly Ustinov <vitaly@ustinov.ca> writes:
> In a BEFORE trigger (PL/pgSQL) I can access not yet computed generated
> columns via the "NEW" whole-row var. I can read from it (NULL), and I
> can write to it, but the assigned value will be ignored.
NEW is not really a whole-row var in the sense that we're discussing
here. In any case, yes, nodeModifyTable runs computation of generated
columns after firing BEFORE triggers. I suppose that's to prevent
the triggers from interfering with those values.
> Is it okay with you that the patch 0002 introduces some inconsistency with that?
In what way would this introduce (new) inconsistency? I didn't move
the computation of those values from where they were. Moreover, so
far as I can see, ATRewriteTable doesn't fire BEFORE triggers at all.
BTW, while looking around nodeModifyTable, I noted some other gaps in our
support for "tableoid" in GENERATED expressions: the FDW code paths in
ExecInsert and ExecUpdate fail to fill tts_tableOid till after running
ExecComputeStoredGenerated. So they have the same bug that 0001 fixes
in ATRewriteTable. It can be fixed the same way, ie move the code
that fills tts_tableOid; but I remain very concerned about how many
other gaps there are.
regards, tom lane
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To: pgsql-bugs@postgresql.org
Cc: tgl@sss.pgh.pa.us, vitaly@ustinov.ca, peter.eisentraut@enterprisedb.com, david.g.johnston@gmail.com
Subject: Re: Generated column is not updated (Postgres 13)
In-Reply-To: <3795805.1621544948@sss.pgh.pa.us>
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