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Introduce custom path and scan providers.

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This allows extension modules to define their own methods for
scanning a relation, and get the core code to use them.  It's
unclear as yet how much use this capability will find, but we
won't find out if we never commit it.

KaiGai Kohei, reviewed at various times and in various levels
of detail by Shigeru Hanada, Tom Lane, Andres Freund, Álvaro
Herrera, and myself.
This commit is contained in:
Robert Haas
2014-11-07 17:26:02 -05:00
parent 7250d8535b
commit 0b03e5951b
22 changed files with 638 additions and 10 deletions
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70
src/backend/utils/adt/ruleutils.c
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@ -5493,6 +5493,26 @@ get_utility_query_def(Query *query, deparse_context *context)
}
}
/*
* GetSpecialCustomVar
*
* If a custom-scan provider uses a special varnode, this function will be
* called when deparsing; it should return an Expr node to be reversed-listed
* in lieu of the special Var.
*/
static Node *
GetSpecialCustomVar(CustomScanState *css, Var *varnode, PlanState **child_ps)
{
Assert(IsA(css, CustomScanState));
Assert(IS_SPECIAL_VARNO(varnode->varno));
if (!css->methods->GetSpecialCustomVar)
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("%s does not support special varno reference",
css->methods->CustomName)));
return (Node *) css->methods->GetSpecialCustomVar(css, varnode, child_ps);
}
/*
* Display a Var appropriately.
@ -5522,6 +5542,8 @@ get_variable(Var *var, int levelsup, bool istoplevel, deparse_context *context)
int netlevelsup;
deparse_namespace *dpns;
deparse_columns *colinfo;
PlanState *child_ps = NULL;
Node *expr;
char *refname;
char *attname;
@ -5546,6 +5568,29 @@ get_variable(Var *var, int levelsup, bool istoplevel, deparse_context *context)
colinfo = deparse_columns_fetch(var->varno, dpns);
attnum = var->varattno;
}
else if (IS_SPECIAL_VARNO(var->varno) &&
IsA(dpns->planstate, CustomScanState) &&
(expr = GetSpecialCustomVar((CustomScanState *) dpns->planstate,
var, &child_ps)) != NULL)
{
deparse_namespace save_dpns;
if (child_ps)
push_child_plan(dpns, child_ps, &save_dpns);
/*
* Force parentheses because our caller probably assumed a Var is a
* simple expression.
*/
if (!IsA(expr, Var))
appendStringInfoChar(buf, '(');
get_rule_expr((Node *) expr, context, true);
if (!IsA(expr, Var))
appendStringInfoChar(buf, ')');
if (child_ps)
pop_child_plan(dpns, &save_dpns);
return NULL;
}
else if (var->varno == OUTER_VAR && dpns->outer_tlist)
{
TargetEntry *tle;
@ -5760,6 +5805,7 @@ get_name_for_var_field(Var *var, int fieldno,
AttrNumber attnum;
int netlevelsup;
deparse_namespace *dpns;
PlanState *child_ps = NULL;
TupleDesc tupleDesc;
Node *expr;
@ -5834,6 +5880,30 @@ get_name_for_var_field(Var *var, int fieldno,
rte = rt_fetch(var->varno, dpns->rtable);
attnum = var->varattno;
}
else if (IS_SPECIAL_VARNO(var->varno) &&
IsA(dpns->planstate, CustomScanState) &&
(expr = GetSpecialCustomVar((CustomScanState *) dpns->planstate,
var, &child_ps)) != NULL)
{
StringInfo saved = context->buf;
StringInfoData temp;
deparse_namespace save_dpns;
initStringInfo(&temp);
context->buf = &temp;
if (child_ps)
push_child_plan(dpns, child_ps, &save_dpns);
if (!IsA(expr, Var))
appendStringInfoChar(context->buf, '(');
get_rule_expr((Node *) expr, context, true);
if (!IsA(expr, Var))
appendStringInfoChar(context->buf, ')');
if (child_ps)
pop_child_plan(dpns, &save_dpns);
context->buf = saved;
return temp.data;
}
else if (var->varno == OUTER_VAR && dpns->outer_tlist)
{
TargetEntry *tle;