Horton

Re: PG 15 (and to a smaller degree 14) regression due to ExprEvalStep size

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: "Jonathan S. Katz" <jkatz@postgresql.org>
Cc: Amit Langote <amitlangote09@gmail.com>, Andrew Dunstan <andrew@dunslane.net>, David Rowley <dgrowleyml@gmail.com>, Alvaro Herrera <alvherre@alvh.no-ip.org>, Michael Paquier <michael@paquier.xyz>, John Naylor <john.naylor@enterprisedb.com>, Tom Lane <tgl@sss.pgh.pa.us>, Peter Geoghegan <pg@bowt.ie>, PostgreSQL-development <pgsql-hackers@postgresql.org>, Nikita Glukhov <n.gluhov@postgrespro.ru>
Date: 2022-08-11T17:17:40Z
Lists: pgsql-hackers 
Hi,

On 2022-08-11 13:08:27 -0400, Jonathan S. Katz wrote:
> On 8/10/22 9:27 AM, Amit Langote wrote:
> > On Wed, Aug 10, 2022 at 3:57 AM Andres Freund <andres@anarazel.de> wrote:
> > > One way this code could be drastically simplified is to force all
> > > type-coercions to go through the "io coercion" path, which could be
> > > implemented as a single execution step (which thus could trivially
> > > start/finish a subtransaction) and would remove a lot of the complicated code
> > > around coercions.
> > 
> > Could you please clarify how you think we might do the io coercion
> > wrapped with a subtransaction all as a single execution step?  I
> > would've thought that we couldn't do the sub-transaction without
> > leaving ExecInterpExpr() anyway, so maybe you meant the io coercion
> > itself was done using some code outside ExecInterpExpr()?
> > 
> > The current JsonExpr code does it by recursively calling
> > ExecInterpExpr() using the nested ExprState expressly for the
> > coercion.

The basic idea is to rip out all the type-dependent stuff out and replace it
with a single JSON_IOCERCE step, which has a parameter about whether to wrap
things in a subtransaction or not. That step would always perform the coercion
by calling the text output function of the input and the text input function
of the output.


> With RMT hat on, Andres do you have any thoughts on this?

I think I need to prototype how it'd look like to give a more detailed
answer. I have a bunch of meetings over the next few hours, but after that I
can give it a shot.

Greetings,

Andres Freund

Commits

  1. JSON_TABLE: Add support for NESTED paths and columns

  2. Add basic JSON_TABLE() functionality

  3. Add SQL/JSON query functions

  4. Add soft error handling to some expression nodes

  5. Adjust populate_record_field() to handle errors softly

  6. Refactor code used by jsonpath executor to fetch variables

  7. Add more SQL/JSON constructor functions

  8. SQL/JSON: support the IS JSON predicate

  9. SQL/JSON: add standard JSON constructor functions

  10. Add static assertion ensuring sizeof(ExprEvalStep) <= 64 bytes

  11. Remove size increase in ExprEvalStep caused by hashed saops

  12. pgstat: reduce timer overhead by leaving timer running.

  13. expression eval: Fix EEOP_JSON_CONSTRUCTOR and EEOP_JSONEXPR size.

  14. SQL/JSON query functions

  15. Speedup ScalarArrayOpExpr evaluation