Date: Mon, 16 Mar 2020 11:17:33 -0300
From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Amit Kapila <amit.kapila16@gmail.com>
Cc: Justin Pryzby <pryzby@telsasoft.com>,
	Masahiko Sawada <masahiko.sawada@2ndquadrant.com>,
	Andres Freund <andres@anarazel.de>,
	Michael Paquier <michael@paquier.xyz>,
	pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: error context for vacuum to include block number
Message-ID: <20200316141733.GA14437@alvherre.pgsql>
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On 2020-Mar-16, Amit Kapila wrote:

> 2.
> + /* Setup error traceback support for ereport() */
> + update_vacuum_error_cbarg(vacrelstats, VACUUM_ERRCB_PHASE_SCAN_HEAP,
> + InvalidBlockNumber, NULL);
> + errcallback.callback = vacuum_error_callback;
> + errcallback.arg = vacrelstats;
> + errcallback.previous = error_context_stack;
> + error_context_stack = &errcallback;
> ..
> ..
> + /* Init vacrelstats for use as error callback by parallel worker: */
> + vacrelstats.relnamespace = get_namespace_name(RelationGetNamespace(onerel));
> + vacrelstats.relname = pstrdup(RelationGetRelationName(onerel));
> + vacrelstats.indname = NULL;
> + vacrelstats.phase = VACUUM_ERRCB_PHASE_UNKNOWN; /* Not yet processing */
> +
> + /* Setup error traceback support for ereport() */
> + errcallback.callback = vacuum_error_callback;
> + errcallback.arg = &vacrelstats;
> + errcallback.previous = error_context_stack;
> + error_context_stack = &errcallback;
> +
> 
> I think the code can be bit simplified if we have a function
> setup_vacuum_error_ctx which takes necessary parameters and fill the
> required vacrelstats params, setup errcallback.  Then we can use
> update_vacuum_error_cbarg at required places.

Heh, he had that and I took it away -- it looked unnatural.  I thought
changing error_context_stack inside such a function, then resetting it
back to "previous" outside the function, was too leaky an abstraction.

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services