http://www.sigaev.ru/misc/builtin_knngist_core-0.9.gz
http://www.sigaev.ru/misc/builtin_knngist_itself-0.8.2.gz
http://www.sigaev.ru/misc/builtin_knngist_proc-0.8.gz
http://www.sigaev.ru/misc/builtin_knngist_contrib_pg_trgm-0.8.gz
http://www.sigaev.ru/misc/builtin_knngist_contrib_btree_gist-0.8.1.gz

>>> +               if (opform->oprresult == BOOLOID)
>>> +                       ereport(ERROR,
>>> +
>>> (errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
>>> +                                        errmsg("index ordering
>>> operators must not return boolean")));

New version allows to use boolean distance, i.e. the same operator could be used 
both in WHERE and ORDER BY clauses. Now operator could present in operator 
family twice, but with different StrategyNumber: as ordinary search operator (in 
WHERE clause) and as an order operator (ORDER BY).
So, list of changes:
1) "pg_amop_opr_fam_index" UNIQUE, btree (amopopr, amopfamily) =>
    "pg_amop_opr_fam_index" UNIQUE, btree (amopopr, amopfamily, amoporder)
2) op_in_opfamily, get_op_opfamily_strategy, get_op_opfamily_properties accept
    one more argument, bool orderop, to point which kind of operator we need to
    find
3) bool OpExpr.orderop. This field is needed to correctly set SK_ORDER flags
    for index scan (ExecIndexBuildScanKeys function). SK_ORDER flag points type
    of tree traversal algorithm to GiST core.

Introducing two fields, per Tom's suggestion, doesn't resolve following issues:
- we still need to distinguish WHERE and ORDER BY operator in
   ExecIndexBuildScanKey, as it done in new version of patch
- When we execute AMOPOPID cache request we still need to check pg_amop.amorder
   or introduce two new indexes (amopopr, amopfamily, amopcanwhere) and
   (amopopr, amopfamily, amopcanorder) and the same changes in lsyscache's
   functions
- If one operation could be used for both usage type then it will be good to
   distinguish them in consistent method. New version requires to use
   different strategy number for each usage type.

-- 
Teodor Sigaev                                   E-mail: teodor(at)sigaev(dot)ru
                                                    WWW: http://www.sigaev.ru/

In response to

• Re: knngist - 0.8 at 2010-09-10 01:08:57 from Robert Haas

Responses

• Re: knngist - 0.8 at 2010-09-15 03:22:58 from Robert Haas
• knngist patch preliminary review (2010-09 commitfest) at 2010-09-22 07:29:55 from Andrew Gierth

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