Horton

Re: support for MERGE

Zhihong Yu <zyu@yugabyte.com>

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From: Zhihong Yu <zyu@yugabyte.com>
To: Álvaro Herrera <alvherre@alvh.no-ip.org>
Cc: Andres Freund <andres@anarazel.de>, "pgsql-hackers@lists.postgresql.org" <pgsql-hackers@lists.postgresql.org>, Simon Riggs <simon.riggs@enterprisedb.com>, Tomas Vondra <tomas.vondra@enterprisedb.com>, Daniel Westermann <dwe@dbi-services.com>, Amit Langote <amitlangote09@gmail.com>, Justin Pryzby <pryzby@telsasoft.com>, Japin Li <japinli@hotmail.com>, Erik Rijkers <er@xs4all.nl>, Jaime Casanova <jcasanov@systemguards.com.ec>
Date: 2022-03-07T22:53:15Z
Lists: pgsql-hackers 
On Mon, Mar 7, 2022 at 12:04 PM Álvaro Herrera <alvherre@alvh.no-ip.org>
wrote:

> On Mon, Mar 7, 2022, at 4:59 PM, Álvaro Herrera wrote:
>
> I attach v13 here.  This version includes a 0002 that's does the split of
> nodeModifyTable.c routines, then 0003 implements MERGE on top of that.
> 0001 is as before.
>
>
> In 0002, I've opted to have two separate structs.  One is the
> ModifyTableContext, as before, but I've removed 'tupleid' and 'oldtuple'
> (the specification of the tuple to delete/update) because it makes
> ExecCrossPartitionUpdate cleaner if we pass them separately.  The second
> struct is UpdateContext, which is used inside ExecUpdate as output data
> from its subroutines.  This is also for the benefit of cross-partition
> updates.
>
> I'm pretty happy with how this turned out; even without considering MERGE,
> it seems to me that ExecUpdate benefits from being shorter.
>
Hi,
For v13-0003-MERGE-SQL-Command-following-SQL-2016.patch :

+    * Reset per-tuple memory context to free any expression evaluation
+    * storage allocated in the previous cycle.
+    */
+   ResetExprContext(econtext);

Why is the memory cleanup done in the next cycle ? Can the cleanup be done
at the end of the current cycle ?

+            * XXX Should this explain why MERGE has the same logic as
UPDATE?

I think explanation should be given.

Cheers

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.