Speed up Hash Join by making ExprStates support hashing

Here we add ExprState support for obtaining a 32-bit hash value from a
list of expressions.  This allows both faster hashing and also JIT
compilation of these expressions.  This is especially useful when hash
joins have multiple join keys as the previous code called ExecEvalExpr on
each hash join key individually and that was inefficient as tuple
deformation would have only taken into account one key at a time, which
could lead to walking the tuple once for each join key.  With the new
code, we'll determine the maximum attribute required and deform the tuple
to that point only once.

Some performance tests done with this change have shown up to a 20%
performance increase of a query containing a Hash Join without JIT
compilation and up to a 26% performance increase when JIT is enabled and
optimization and inlining were performed by the JIT compiler.  The
performance increase with 1 join column was less with a 14% increase
with and without JIT.  This test was done using a fairly small hash
table and a large number of hash probes.  The increase will likely be
less with large tables, especially ones larger than L3 cache as memory
pressure is more likely to be the limiting factor there.

This commit only addresses Hash Joins, but lays expression evaluation
and JIT compilation infrastructure for other hashing needs such as Hash
Aggregate.

Author: David Rowley
Reviewed-by: Alexey Dvoichenkov <alexey@hyperplane.net>
Reviewed-by: Tels <nospam-pg-abuse@bloodgate.com>
Discussion: https://postgr.es/m/CAApHDvoexAxgQFNQD_GRkr2O_eJUD1-wUGm%3Dm0L%2BGc%3DT%3DkEa4g%40mail.gmail.com

1 files changed, 24 insertions, 0 deletions

diff --git a/src/include/executor/execExpr.h b/src/include/executor/execExpr.h
index 845f3422dea..eec0aa699e5 100644
--- a/src/include/executor/execExpr.h
+++ b/src/include/executor/execExpr.h
@@ -235,6 +235,13 @@ typedef enum ExprEvalOp
 	/* evaluate a single domain CHECK constraint */
 	EEOP_DOMAIN_CHECK,
 
+	/* evaluation steps for hashing */
+	EEOP_HASHDATUM_SET_INITVAL,
+	EEOP_HASHDATUM_FIRST,
+	EEOP_HASHDATUM_FIRST_STRICT,
+	EEOP_HASHDATUM_NEXT32,
+	EEOP_HASHDATUM_NEXT32_STRICT,
+
 	/* evaluate assorted special-purpose expression types */
 	EEOP_CONVERT_ROWTYPE,
 	EEOP_SCALARARRAYOP,
@@ -558,6 +565,23 @@ typedef struct ExprEvalStep
 			ErrorSaveContext *escontext;
 		}			domaincheck;
 
+		/* for EEOP_HASH_SET_INITVAL */
+		struct
+		{
+			Datum		init_value;
+
+		}			hashdatum_initvalue;
+
+		/* for EEOP_HASHDATUM_(FIRST|NEXT32)[_STRICT] */
+		struct
+		{
+			FmgrInfo   *finfo;	/* function's lookup data */
+			FunctionCallInfo fcinfo_data;	/* arguments etc */
+			/* faster to access without additional indirection: */
+			PGFunction	fn_addr;	/* actual call address */
+			int			jumpdone;	/* jump here on null */
+		}			hashdatum;
+
 		/* for EEOP_CONVERT_ROWTYPE */
 		struct
 		{