Faster expression evaluation and targetlist projection.

This replaces the old, recursive tree-walk based evaluation, with
non-recursive, opcode dispatch based, expression evaluation.
Projection is now implemented as part of expression evaluation.

This both leads to significant performance improvements, and makes
future just-in-time compilation of expressions easier.

The speed gains primarily come from:
- non-recursive implementation reduces stack usage / overhead
- simple sub-expressions are implemented with a single jump, without
  function calls
- sharing some state between different sub-expressions
- reduced amount of indirect/hard to predict memory accesses by laying
  out operation metadata sequentially; including the avoidance of
  nearly all of the previously used linked lists
- more code has been moved to expression initialization, avoiding
  constant re-checks at evaluation time

Future just-in-time compilation (JIT) has become easier, as
demonstrated by released patches intended to be merged in a later
release, for primarily two reasons: Firstly, due to a stricter split
between expression initialization and evaluation, less code has to be
handled by the JIT. Secondly, due to the non-recursive nature of the
generated "instructions", less performance-critical code-paths can
easily be shared between interpreted and compiled evaluation.

The new framework allows for significant future optimizations. E.g.:
- basic infrastructure for to later reduce the per executor-startup
  overhead of expression evaluation, by caching state in prepared
  statements.  That'd be helpful in OLTPish scenarios where
  initialization overhead is measurable.
- optimizing the generated "code". A number of proposals for potential
  work has already been made.
- optimizing the interpreter. Similarly a number of proposals have
  been made here too.

The move of logic into the expression initialization step leads to some
backward-incompatible changes:
- Function permission checks are now done during expression
  initialization, whereas previously they were done during
  execution. In edge cases this can lead to errors being raised that
  previously wouldn't have been, e.g. a NULL array being coerced to a
  different array type previously didn't perform checks.
- The set of domain constraints to be checked, is now evaluated once
  during expression initialization, previously it was re-built
  every time a domain check was evaluated. For normal queries this
  doesn't change much, but e.g. for plpgsql functions, which caches
  ExprStates, the old set could stick around longer.  The behavior
  around might still change.

Author: Andres Freund, with significant changes by Tom Lane,
	changes by Heikki Linnakangas
Reviewed-By: Tom Lane, Heikki Linnakangas
Discussion: https://postgr.es/m/[email protected]

1 files changed, 150 insertions, 28 deletions

diff --git a/src/include/executor/executor.h b/src/include/executor/executor.h
index a5c75e771f0..d3849b93eb1 100644
--- a/src/include/executor/executor.h
+++ b/src/include/executor/executor.h
@@ -65,15 +65,6 @@
 #define EXEC_FLAG_WITH_NO_DATA	0x0080	/* rel scannability doesn't matter */
 
 
-/*
- * ExecEvalExpr was formerly a function containing a switch statement;
- * now it's just a macro invoking the function pointed to by an ExprState
- * node.  Beware of double evaluation of the ExprState argument!
- */
-#define ExecEvalExpr(expr, econtext, isNull) \
-	((*(expr)->evalfunc) (expr, econtext, isNull))
-
-
 /* Hook for plugins to get control in ExecutorStart() */
 typedef void (*ExecutorStart_hook_type) (QueryDesc *queryDesc, int eflags);
 extern PGDLLIMPORT ExecutorStart_hook_type ExecutorStart_hook;
@@ -242,29 +233,155 @@ extern void ExecEndNode(PlanState *node);
 extern bool ExecShutdownNode(PlanState *node);
 
 /*
- * prototypes from functions in execQual.c
+ * prototypes from functions in execExpr.c
  */
-extern Datum GetAttributeByNum(HeapTupleHeader tuple, AttrNumber attrno,
-				  bool *isNull);
-extern Datum GetAttributeByName(HeapTupleHeader tuple, const char *attname,
-				   bool *isNull);
-extern Tuplestorestate *ExecMakeTableFunctionResult(ExprState *funcexpr,
+extern ExprState *ExecInitExpr(Expr *node, PlanState *parent);
+extern ExprState *ExecInitQual(List *qual, PlanState *parent);
+extern ExprState *ExecInitCheck(List *qual, PlanState *parent);
+extern List *ExecInitExprList(List *nodes, PlanState *parent);
+extern ProjectionInfo *ExecBuildProjectionInfo(List *targetList,
+						ExprContext *econtext,
+						TupleTableSlot *slot,
+						PlanState *parent,
+						TupleDesc inputDesc);
+extern ExprState *ExecPrepareExpr(Expr *node, EState *estate);
+extern ExprState *ExecPrepareQual(List *qual, EState *estate);
+extern ExprState *ExecPrepareCheck(List *qual, EState *estate);
+extern List *ExecPrepareExprList(List *nodes, EState *estate);
+
+/*
+ * ExecEvalExpr
+ *
+ * Evaluate expression identified by "state" in the execution context
+ * given by "econtext".  *isNull is set to the is-null flag for the result,
+ * and the Datum value is the function result.
+ *
+ * The caller should already have switched into the temporary memory
+ * context econtext->ecxt_per_tuple_memory.  The convenience entry point
+ * ExecEvalExprSwitchContext() is provided for callers who don't prefer to
+ * do the switch in an outer loop.
+ */
+#ifndef FRONTEND
+static inline Datum
+ExecEvalExpr(ExprState *state,
+			 ExprContext *econtext,
+			 bool *isNull)
+{
+	return (*state->evalfunc) (state, econtext, isNull);
+}
+#endif
+
+/*
+ * ExecEvalExprSwitchContext
+ *
+ * Same as ExecEvalExpr, but get into the right allocation context explicitly.
+ */
+#ifndef FRONTEND
+static inline Datum
+ExecEvalExprSwitchContext(ExprState *state,
+						  ExprContext *econtext,
+						  bool *isNull)
+{
+	Datum		retDatum;
+	MemoryContext oldContext;
+
+	oldContext = MemoryContextSwitchTo(econtext->ecxt_per_tuple_memory);
+	retDatum = (*state->evalfunc) (state, econtext, isNull);
+	MemoryContextSwitchTo(oldContext);
+	return retDatum;
+}
+#endif
+
+/*
+ * ExecProject
+ *
+ * Projects a tuple based on projection info and stores it in the slot passed
+ * to ExecBuildProjectInfo().
+ *
+ * Note: the result is always a virtual tuple; therefore it may reference
+ * the contents of the exprContext's scan tuples and/or temporary results
+ * constructed in the exprContext.  If the caller wishes the result to be
+ * valid longer than that data will be valid, he must call ExecMaterializeSlot
+ * on the result slot.
+ */
+#ifndef FRONTEND
+static inline TupleTableSlot *
+ExecProject(ProjectionInfo *projInfo)
+{
+	ExprContext *econtext = projInfo->pi_exprContext;
+	ExprState  *state = &projInfo->pi_state;
+	TupleTableSlot *slot = state->resultslot;
+	bool		isnull;
+
+	/*
+	 * Clear any former contents of the result slot.  This makes it safe for
+	 * us to use the slot's Datum/isnull arrays as workspace.
+	 */
+	ExecClearTuple(slot);
+
+	/* Run the expression, discarding scalar result from the last column. */
+	(void) ExecEvalExprSwitchContext(state, econtext, &isnull);
+
+	/*
+	 * Successfully formed a result row.  Mark the result slot as containing a
+	 * valid virtual tuple (inlined version of ExecStoreVirtualTuple()).
+	 */
+	slot->tts_isempty = false;
+	slot->tts_nvalid = slot->tts_tupleDescriptor->natts;
+
+	return slot;
+}
+#endif
+
+/*
+ * ExecQual - evaluate a qual prepared with ExecInitQual (possibly via
+ * ExecPrepareQual).  Returns true if qual is satisfied, else false.
+ *
+ * Note: ExecQual used to have a third argument "resultForNull".  The
+ * behavior of this function now corresponds to resultForNull == false.
+ * If you want the resultForNull == true behavior, see ExecCheck.
+ */
+#ifndef FRONTEND
+static inline bool
+ExecQual(ExprState *state, ExprContext *econtext)
+{
+	Datum		ret;
+	bool		isnull;
+
+	/* short-circuit (here and in ExecInitQual) for empty restriction list */
+	if (state == NULL)
+		return true;
+
+	/* verify that expression was compiled using ExecInitQual */
+	Assert(state->flags & EEO_FLAG_IS_QUAL);
+
+	ret = ExecEvalExprSwitchContext(state, econtext, &isnull);
+
+	/* EEOP_QUAL should never return NULL */
+	Assert(!isnull);
+
+	return DatumGetBool(ret);
+}
+#endif
+
+extern bool ExecCheck(ExprState *state, ExprContext *context);
+
+/*
+ * prototypes from functions in execSRF.c
+ */
+extern SetExprState *ExecInitTableFunctionResult(Expr *expr,
+							ExprContext *econtext, PlanState *parent);
+extern Tuplestorestate *ExecMakeTableFunctionResult(SetExprState *setexpr,
 							ExprContext *econtext,
 							MemoryContext argContext,
 							TupleDesc expectedDesc,
 							bool randomAccess);
-extern Datum ExecMakeFunctionResultSet(FuncExprState *fcache,
+extern SetExprState *ExecInitFunctionResultSet(Expr *expr,
+						  ExprContext *econtext, PlanState *parent);
+extern Datum ExecMakeFunctionResultSet(SetExprState *fcache,
 						  ExprContext *econtext,
 						  bool *isNull,
 						  ExprDoneCond *isDone);
-extern Datum ExecEvalExprSwitchContext(ExprState *expression, ExprContext *econtext,
-						  bool *isNull);
-extern ExprState *ExecInitExpr(Expr *node, PlanState *parent);
-extern ExprState *ExecPrepareExpr(Expr *node, EState *estate);
-extern bool ExecQual(List *qual, ExprContext *econtext, bool resultForNull);
-extern int	ExecTargetListLength(List *targetlist);
-extern int	ExecCleanTargetListLength(List *targetlist);
-extern TupleTableSlot *ExecProject(ProjectionInfo *projInfo);
 
 /*
  * prototypes from functions in execScan.c
@@ -355,10 +472,6 @@ extern void ExecAssignExprContext(EState *estate, PlanState *planstate);
 extern void ExecAssignResultType(PlanState *planstate, TupleDesc tupDesc);
 extern void ExecAssignResultTypeFromTL(PlanState *planstate);
 extern TupleDesc ExecGetResultType(PlanState *planstate);
-extern ProjectionInfo *ExecBuildProjectionInfo(List *targetList,
-						ExprContext *econtext,
-						TupleTableSlot *slot,
-						TupleDesc inputDesc);
 extern void ExecAssignProjectionInfo(PlanState *planstate,
 						 TupleDesc inputDesc);
 extern void ExecFreeExprContext(PlanState *planstate);
@@ -376,8 +489,17 @@ extern void RegisterExprContextCallback(ExprContext *econtext,
 extern void UnregisterExprContextCallback(ExprContext *econtext,
 							  ExprContextCallbackFunction function,
 							  Datum arg);
+
 extern void ExecLockNonLeafAppendTables(List *partitioned_rels, EState *estate);
 
+extern Datum GetAttributeByName(HeapTupleHeader tuple, const char *attname,
+				   bool *isNull);
+extern Datum GetAttributeByNum(HeapTupleHeader tuple, AttrNumber attrno,
+				  bool *isNull);
+
+extern int	ExecTargetListLength(List *targetlist);
+extern int	ExecCleanTargetListLength(List *targetlist);
+
 /*
  * prototypes from functions in execIndexing.c
  */