Horton

Re: support for MERGE

Alvaro Herrera <alvherre@alvh.no-ip.org>

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From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Japin Li <japinli@hotmail.com>
Cc: Erik Rijkers <er@xs4all.nl>, Andrew Dunstan <andrew@dunslane.net>, Simon Riggs <simon.riggs@enterprisedb.com>, Tomas Vondra <tomas.vondra@enterprisedb.com>, Zhihong Yu <zyu@yugabyte.com>, Daniel Westermann <dwe@dbi-services.com>, Amit Langote <amitlangote09@gmail.com>, Justin Pryzby <pryzby@telsasoft.com>, Pavan Deolasee <pavan.deolasee@gmail.com>, pgsql-hackers@lists.postgresql.org
Date: 2022-01-20T21:02:22Z
Lists: pgsql-hackers 
On 2022-Jan-17, Japin Li wrote:

> So for NOT MATCHED, we are expected not use the target table columns.
> 
> The code comes from execMerge.c says:
> 
>     /*
>      * Make source tuple available to ExecQual and ExecProject. We don't need
>      * the target tuple, since the WHEN quals and the targetlist can't refer to
>      * the target columns.
>      */
>     econtext->ecxt_scantuple = NULL;
>     econtext->ecxt_innertuple = slot;
>     econtext->ecxt_outertuple = NULL;
> 
> It will set econtext->ecxt_scantuple to NULL, which leads the crash.

Right.  So this was broken by the fact that I recently allowed MATCHED
actions to target DO NOTHING; previously, only NOT MATCHED actions could
do so.  So the bug was present, but it wasn't accessible.

> Should we setNamespaceVisibilityForRTE() for CMD_NOTHING?  I try to set it
> and it works as expected.  OTOH, the system attributes from target table
> also cannot be accessible.  I'm not sure the v6 patch how to implement this
> limitation.

I changed this block so that it depends on whether the clause is MATCHED
or NOT MATCHED, rather than the action.  I think it was pretty
nonsensical for it to be keyed on action type, and it made the code
needlessly longer.

Thank you!

-- 
Álvaro Herrera              Valdivia, Chile  —  https://www.EnterpriseDB.com/
"All rings of power are equal,
But some rings of power are more equal than others."
                                 (George Orwell's The Lord of the Rings)

Commits

  1. Doc fixes for MERGE statement

  2. MERGE docs adjustments

  3. Link to MVCC docs in MERGE docs

  4. Fix EXPLAIN MERGE output when no tuples are processed

  5. Make EXPLAIN MERGE output format more compact

  6. Add support for MERGE SQL command

  7. Split ExecUpdate and ExecDelete into reusable pieces

  8. Add API of sorts for transition table handling in trigger.c

  9. Represent Lists as expansible arrays, not chains of cons-cells.