Horton

Re: remaining sql/json patches

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

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From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Amit Langote <amitlangote09@gmail.com>
Cc: Andrew Dunstan <andrew@dunslane.net>, jian he <jian.universality@gmail.com>, Erik Rijkers <er@xs4all.nl>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2023-09-21T08:57:54Z
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.

I keep looking at 0001, and in the struct definition I think putting the
escontext at the bottom is not great, because there's a comment a few
lines above that says "XXX: following fields only needed during
"compilation"), could be thrown away afterwards".  This comment is not
strictly true, because innermost_caseval is actually used by
array_map(); yet it seems that ->escontext should appear before that
comment.

However, if you put it before steps_len, it would push members steps_len
and steps_alloc beyond the struct's first cache line(*).  If those
struct members are critical for expression init performance, then maybe
it's not a good tradeoff.  I don't know if this was struct laid out
carefully with that consideration in mind or not.

Also, ->escontext's own comment in ExprState seems to be saying too much
and not saying enough.  I would reword it as "For expression nodes that
support soft errors.  NULL if caller wants them thrown instead".  The
shortest I could make so that it fits in a single is "For nodes that can
error softly. NULL if caller wants them thrown", or "For
soft-error-enabled nodes.  NULL if caller wants errors thrown".  Not
sure if those are good enough, or just make the comment the whole four
lines ...


(*) This is what pahole says about the struct as 0001 would put it:

struct ExprState {
    NodeTag                    type;                 /*     0     4 */
    uint8                      flags;                /*     4     1 */
    _Bool                      resnull;              /*     5     1 */

    /* XXX 2 bytes hole, try to pack */

    Datum                      resvalue;             /*     8     8 */
    TupleTableSlot *           resultslot;           /*    16     8 */
    struct ExprEvalStep *      steps;                /*    24     8 */
    ExprStateEvalFunc          evalfunc;             /*    32     8 */
    Expr *                     expr;                 /*    40     8 */
    void *                     evalfunc_private;     /*    48     8 */
    int                        steps_len;            /*    56     4 */
    int                        steps_alloc;          /*    60     4 */
    /* --- cacheline 1 boundary (64 bytes) --- */
    struct PlanState *         parent;               /*    64     8 */
    ParamListInfo              ext_params;           /*    72     8 */
    Datum *                    innermost_caseval;    /*    80     8 */
    _Bool *                    innermost_casenull;   /*    88     8 */
    Datum *                    innermost_domainval;  /*    96     8 */
    _Bool *                    innermost_domainnull; /*   104     8 */
    ErrorSaveContext *         escontext;            /*   112     8 */

    /* size: 120, cachelines: 2, members: 18 */
    /* sum members: 118, holes: 1, sum holes: 2 */
    /* last cacheline: 56 bytes */
};

-- 
Álvaro Herrera        Breisgau, Deutschland  —  https://www.EnterpriseDB.com/
"Nunca se desea ardientemente lo que solo se desea por razón" (F. Alexandre)