Horton

Re: remaining sql/json patches

Tomas Vondra <tomas.vondra@enterprisedb.com>

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From: Tomas Vondra <tomas.vondra@enterprisedb.com>
To: Amit Langote <amitlangote09@gmail.com>
Cc: Alvaro Herrera <alvherre@alvh.no-ip.org>, Erik Rijkers <er@xs4all.nl>, jian he <jian.universality@gmail.com>, Andres Freund <andres@anarazel.de>, Andrew Dunstan <andrew@dunslane.net>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2024-03-07T11:02:27Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. SQL/JSON: Various improvements to SQL/JSON query function docs

  2. SQL/JSON: Fix some obsolete comments.

  3. SQL/JSON: Fix issues with DEFAULT .. ON ERROR / EMPTY

  4. JSON_TABLE: Add support for NESTED paths and columns

  5. Fix JsonExpr deparsing to emit QUOTES and WRAPPER correctly

  6. Fix typo introduced in 6185c9737

  7. Add basic JSON_TABLE() functionality

  8. Avoid splitting errmsg string to span multiple lines

  9. Add SQL/JSON query functions

  10. Implement various jsonpath methods

  11. Add soft error handling to some expression nodes

  12. Adjust populate_record_field() to handle errors softly

  13. Refactor code used by jsonpath executor to fetch variables

  14. Test EXPLAIN (FORMAT JSON) ... XMLTABLE

  15. Simplify productions for FORMAT JSON [ ENCODING name ]

  16. Add trailing commas to enum definitions

  17. doc: add missing <returnvalue> and whitespace

  18. Add more SQL/JSON constructor functions

  19. Rename a nonterminal used in SQL/JSON grammar

  20. Some refactoring to export json(b) conversion functions

  21. Don't include CaseTestExpr in JsonValueExpr.formatted_expr

  22. Code review for commit b6e1157e7d

  23. Pass constructName to transformJsonValueExpr()

  24. Unify JSON categorize type API and export for external use

  25. Make some indentation in gram.y consistent

  26. Allow most keywords to be used as column labels without requiring AS.

  27. Reduce size of backend scanner's tables.

  28. Use perfect hashing, instead of binary search, for keyword lookup.

Attachments


On 3/7/24 08:26, Amit Langote wrote:
> On Wed, Mar 6, 2024 at 1:07 PM Amit Langote <amitlangote09@gmail.com> wrote:
>> Hi Tomas,
>>
>> On Wed, Mar 6, 2024 at 6:30 AM Tomas Vondra
>> <tomas.vondra@enterprisedb.com> wrote:
>>> I'd say 2.5GB in ExecutorState seems a bit excessive ... Seems there's
>>> some memory management issue? My guess is we're not releasing memory
>>> allocated while parsing the JSON or building JSON output.
>>>
>>> I'm not attaching the data, but I can provide that if needed - it's
>>> about 600MB compressed. The structure is not particularly complex, it's
>>> movie info from [1] combined into a JSON document (one per movie).
>>
>> Thanks for the report.
>>
>> Yeah, I'd like to see the data to try to drill down into what's piling
>> up in ExecutorState.  I want to be sure of if the 1st, query functions
>> patch, is not implicated in this, because I'd like to get that one out
>> of the way sooner than later.
> 
> I tracked this memory-hogging down to a bug in the query functions
> patch (0001) after all.  The problem was with a query-lifetime cache
> variable that was never set to point to the allocated memory.  So a
> struct was allocated and then not freed for every row where it should
> have only been allocated once.
> 

Thanks! I can confirm the query works with the new patches.

Exporting the 7GB table takes ~250 seconds (the result is ~10.6GB). That
seems maybe a bit much, but I'm not sure it's the fault of this patch.
Attached is a flamegraph for the export, and clearly most of the time is
spent in jsonpath. I wonder if there's a way to improve this, but I
don't think it's up to this patch.


regards

-- 
Tomas Vondra
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