Feedback-ID: ia2694551:Fastmail
Date: Wed, 6 Sep 2023 17:01:06 +0200
From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Amit Langote <amitlangote09@gmail.com>
Cc: Erik Rijkers <er@xs4all.nl>, jian he <jian.universality@gmail.com>, 
	Andrew Dunstan <andrew@dunslane.net>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: remaining sql/json patches
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0001 is quite mysterious to me.  I've been reading it but I'm not sure I
grok it, so I don't have anything too intelligent to say about it at
this point.  But here are my thoughts anyway.

Assert()ing that a pointer is not null, and in the next line
dereferencing that pointer, is useless: the process would crash anyway
at the time of dereference, so the Assert() adds no value.  Better to
leave the assert out.  (This appears both in ExecExprEnableErrorSafe and
ExecExprDisableErrorSafe).

Is it not a problem to set just the node type, and not reset the
contents of the node to zeroes, in ExecExprEnableErrorSafe?  I'm not
sure if it's possible to enable error-safe on a node two times with an
error reported in between; would that result in the escontext filled
with junk the second time around?  That might be dangerous.  Maybe a
simple cross-check is to verify (assert) in ExecExprEnableErrorSafe()
that the struct is already all-zeroes, so that if this happens, we'll
get reports about it.  (After all, there are very few nodes that handle
the SOFT_ERROR_OCCURRED case).

Do we need to have the ->details_wanted flag turned on?  Maybe if we're
having ExecExprEnableErrorSafe() as a generic tool, it should receive
the boolean to use as an argument.

Why palloc the escontext always, and not just when
ExecExprEnableErrorSafe is called?  (At Disable time, just memset it to
zero, and next time it is enabled for that node, we don't need to
allocate it again, just set the nodetype.)

ExecExprEnableErrorSafe() is a strange name for this operation.  Maybe
you mean ExecExprEnableSoftErrors()?  Maybe it'd be better to leave it
as NULL initially, so that for the majority of cases we don't even
allocate it.

In 0002 you're adding soft-error support for a bunch of existing
operations, in addition to introducing SQL/JSON query functions.  Maybe
the soft-error stuff should be done separately in a preparatory patch.

I think functions such as populate_array_element() that can now save
soft errors and which currently do not have a return value, should
acquire a convention to let caller know that things failed: maybe return
false if SOFT_ERROR_OCCURRED().  Otherwise it appears that, for instance
populate_array_dim_jsonb() can return happily if an error occurs when
parsing the last element in the array.  Splitting 0002 to have a
preparatory patch where all such soft-error-saving changes are
introduced separately would help review that this is indeed being
handled by all their callers.

-- 
Álvaro Herrera        Breisgau, Deutschland  —  https://www.EnterpriseDB.com/
"Por suerte hoy explotó el califont porque si no me habría muerto
 de aburrido"  (Papelucho)