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Redesign API presented by nodeAgg.c for ordered-set and similar aggregates.

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The previous design exposed the input and output ExprContexts of the
Agg plan node, but work on grouping sets has suggested that we'll regret
doing that.  Instead provide more narrowly-defined APIs that can be
implemented in multiple ways, namely a way to get a short-term memory
context and a way to register an aggregate shutdown callback.

Back-patch to 9.4 where the bad APIs were introduced, since we don't
want third-party code using these APIs and then having to change in 9.5.

Andrew Gierth
This commit is contained in:
Tom Lane
2014-07-03 18:25:33 -04:00
parent 8b6010b835
commit 6f5034eda0
3 changed files with 34 additions and 28 deletions
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38
src/backend/executor/nodeAgg.c
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@ -2199,44 +2199,56 @@ AggGetAggref(FunctionCallInfo fcinfo)
}
/*
* AggGetPerTupleEContext - fetch per-input-tuple ExprContext
* AggGetTempMemoryContext - fetch short-term memory context for aggregates
*
* This is useful in agg final functions; the econtext returned is the
* same per-tuple context that the transfn was called in (which can
* safely get reset during the final function).
* This is useful in agg final functions; the context returned is one that
* the final function can safely reset as desired. This isn't useful for
* transition functions, since the context returned MAY (we don't promise)
* be the same as the context those are called in.
*
* As above, this is currently not useful for aggs called as window functions.
*/
ExprContext *
AggGetPerTupleEContext(FunctionCallInfo fcinfo)
MemoryContext
AggGetTempMemoryContext(FunctionCallInfo fcinfo)
{
if (fcinfo->context && IsA(fcinfo->context, AggState))
{
AggState *aggstate = (AggState *) fcinfo->context;
return aggstate->tmpcontext;
return aggstate->tmpcontext->ecxt_per_tuple_memory;
}
return NULL;
}
/*
* AggGetPerAggEContext - fetch per-output-tuple ExprContext
* AggRegisterCallback - register a cleanup callback for an aggregate
*
* This is useful for aggs to register shutdown callbacks, which will ensure
* that non-memory resources are freed.
* that non-memory resources are freed. The callback will occur just before
* the associated aggcontext (as returned by AggCheckCallContext) is reset,
* either between groups or as a result of rescanning the query. The callback
* will NOT be called on error paths. The typical use-case is for freeing of
* tuplestores or tuplesorts maintained in aggcontext, or pins held by slots
* created by the agg functions. (The callback will not be called until after
* the result of the finalfn is no longer needed, so it's safe for the finalfn
* to return data that will be freed by the callback.)
*
* As above, this is currently not useful for aggs called as window functions.
*/
ExprContext *
AggGetPerAggEContext(FunctionCallInfo fcinfo)
void
AggRegisterCallback(FunctionCallInfo fcinfo,
ExprContextCallbackFunction func,
Datum arg)
{
if (fcinfo->context && IsA(fcinfo->context, AggState))
{
AggState *aggstate = (AggState *) fcinfo->context;
return aggstate->ss.ps.ps_ExprContext;
RegisterExprContextCallback(aggstate->ss.ps.ps_ExprContext, func, arg);
return;
}
return NULL;
elog(ERROR, "aggregate function cannot register a callback in this context");
}