Add general purpose hasing functions to pgbench.

Hashing function is useful for simulating real-world workload in test like
WEB workload, as an example - YCSB benchmarks.

Author: Ildar Musin with minor editorization by me
Reviewed by: Fabien Coelho, me
Discussion: https://www.postgresql.org/message-id/flat/0e8bd39e-dfcd-2879-f88f-272799ad7ef2@postgrespro.ru

Author: feodor

doc/src/sgml/ref/pgbench.sgml

@@ -874,13 +874,18 @@ pgbench <optional> <replaceable>options</replaceable> </optional> <replaceable>d
 
      <tbody>
       <row>
-       <entry> <literal>scale</literal> </entry>
-       <entry>current scale factor</entry>
+       <entry> <literal>client_id</literal> </entry>
+       <entry>unique number identifying the client session (starts from zero)</entry>
       </row>
 
       <row>
-       <entry> <literal>client_id</literal> </entry>
-       <entry>unique number identifying the client session (starts from zero)</entry>
+       <entry> <literal>default_seed</literal> </entry>
+       <entry>seed used in hash functions by default</entry>
+      </row>
+
+      <row>
+       <entry> <literal>scale</literal> </entry>
+       <entry>current scale factor</entry>
       </row>
      </tbody>
     </tgroup>
@@ -1245,6 +1250,27 @@ pgbench <optional> <replaceable>options</replaceable> </optional> <replaceable>d
        <entry><literal>greatest(5, 4, 3, 2)</literal></entry>
        <entry><literal>5</literal></entry>
       </row>
+      <row>
+       <entry><literal><function>hash(<replaceable>a</replaceable> [, <replaceable>seed</replaceable> ] )</function></literal></entry>
+       <entry>integer</entry>
+       <entry>alias for <literal>hash_murmur2()</literal></entry>
+       <entry><literal>hash(10, 5432)</literal></entry>
+       <entry><literal>-5817877081768721676</literal></entry>
+      </row>
+      <row>
+       <entry><literal><function>hash_fnv1a(<replaceable>a</replaceable> [, <replaceable>seed</replaceable> ] )</function></literal></entry>
+       <entry>integer</entry>
+       <entry><ulink url="https://en.wikipedia.org/wiki/Fowler%E2%80%93Noll%E2%80%93Vo_hash_function">FNV-1a hash</ulink></entry>
+       <entry><literal>hash_fnv1a(10, 5432)</literal></entry>
+       <entry><literal>-7793829335365542153</literal></entry>
+      </row>
+      <row>
+       <entry><literal><function>hash_murmur2(<replaceable>a</replaceable> [, <replaceable>seed</replaceable> ] )</function></literal></entry>
+       <entry>integer</entry>
+       <entry><ulink url="https://en.wikipedia.org/wiki/MurmurHash">MurmurHash2 hash</ulink></entry>
+       <entry><literal>hash_murmur2(10, 5432)</literal></entry>
+       <entry><literal>-5817877081768721676</literal></entry>
+      </row>
       <row>
        <entry><literal><function>int(<replaceable>x</replaceable>)</function></literal></entry>
        <entry>integer</entry>
@@ -1423,6 +1449,31 @@ f(x) = PHI(2.0 * parameter * (x - mu) / (max - min + 1)) /
     </listitem>
    </itemizedlist>
 
+  <para>
+    Hash functions <literal>hash</literal>, <literal>hash_murmur2</literal> and
+    <literal>hash_fnv1a</literal> accept an input value and an optional seed parameter.
+    In case the seed isn't provided the value of <literal>:default_seed</literal>
+    is used, which is initialized randomly unless set by the command-line
+    <literal>-D</literal> option. Hash functions can be used to scatter the
+    distribution of random functions such as <literal>random_zipfian</literal> or
+    <literal>random_exponential</literal>. For instance, the following pgbench
+    script simulates possible real world workload typical for social media and
+    blogging platforms where few accounts generate excessive load:
+
+<programlisting>
+\set r random_zipfian(0, 100000000, 1.07)
+\set k abs(hash(:r)) % 1000000
+</programlisting>
+
+    In some cases several distinct distributions are needed which don't correlate
+    with each other and this is when implicit seed parameter comes in handy:
+
+<programlisting>
+\set k1 abs(hash(:r), :default_seed + 123) % 1000000
+\set k2 abs(hash(:r), :default_seed + 321) % 1000000
+</programlisting>
+  </para>
+
   <para>
    As an example, the full definition of the built-in TPC-B-like
    transaction is:

src/bin/pgbench/exprparse.y

@@ -16,6 +16,10 @@
 
 #include "pgbench.h"
 
+#define PGBENCH_NARGS_VARIABLE	(-1)
+#define PGBENCH_NARGS_CASE		(-2)
+#define PGBENCH_NARGS_HASH		(-3)
+
 PgBenchExpr *expr_parse_result;
 
 static PgBenchExprList *make_elist(PgBenchExpr *exp, PgBenchExprList *list);
@@ -226,9 +230,13 @@ make_uop(yyscan_t yyscanner, const char *operator, PgBenchExpr *expr)
 /*
  * List of available functions:
  * - fname: function name, "!..." for special internal functions
- * - nargs: number of arguments
- *			-1 is a special value for least & greatest meaning #args >= 1
- *			-2 is for the "CASE WHEN ..." function, which has #args >= 3 and odd
+ * - nargs: number of arguments. Special cases:
+ *			- PGBENCH_NARGS_VARIABLE is a special value for least & greatest
+ *			  meaning #args >= 1;
+ *			- PGBENCH_NARGS_CASE is for the "CASE WHEN ..." function, which
+ *			  has #args >= 3 and odd;
+ * 			- PGBENCH_NARGS_HASH is for hash functions, which have one required
+ *			  and one optional argument;
  * - tag: function identifier from PgBenchFunction enum
  */
 static const struct
@@ -259,10 +267,10 @@ static const struct
 		"abs", 1, PGBENCH_ABS
 	},
 	{
-		"least", -1, PGBENCH_LEAST
+		"least", PGBENCH_NARGS_VARIABLE, PGBENCH_LEAST
 	},
 	{
-		"greatest", -1, PGBENCH_GREATEST
+		"greatest", PGBENCH_NARGS_VARIABLE, PGBENCH_GREATEST
 	},
 	{
 		"debug", 1, PGBENCH_DEBUG
@@ -347,7 +355,25 @@ static const struct
 	},
 	/* "case when ... then ... else ... end" construction */
 	{
-		"!case_end", -2, PGBENCH_CASE
+		"!case_end", PGBENCH_NARGS_CASE, PGBENCH_CASE
+	},
+	{
+		"hash", PGBENCH_NARGS_HASH, PGBENCH_HASH_MURMUR2
+	},
+	{
+		"hash_murmur2", PGBENCH_NARGS_HASH, PGBENCH_HASH_MURMUR2
+	},
+	{
+		"hash_fnv1a", PGBENCH_NARGS_HASH, PGBENCH_HASH_FNV1A
+	},
+	{
+		"hash", PGBENCH_NARGS_HASH, PGBENCH_HASH_MURMUR2
+	},
+	{
+		"hash_murmur2", PGBENCH_NARGS_HASH, PGBENCH_HASH_MURMUR2
+	},
+	{
+		"hash_fnv1a", PGBENCH_NARGS_HASH, PGBENCH_HASH_FNV1A
 	},
 	/* keep as last array element */
 	{
@@ -423,29 +449,51 @@ elist_length(PgBenchExprList *list)
 static PgBenchExpr *
 make_func(yyscan_t yyscanner, int fnumber, PgBenchExprList *args)
 {
+	int len = elist_length(args);
+
 	PgBenchExpr *expr = pg_malloc(sizeof(PgBenchExpr));
 
 	Assert(fnumber >= 0);
 
-	if (PGBENCH_FUNCTIONS[fnumber].nargs >= 0 &&
-		PGBENCH_FUNCTIONS[fnumber].nargs != elist_length(args))
-		expr_yyerror_more(yyscanner, "unexpected number of arguments",
-						  PGBENCH_FUNCTIONS[fnumber].fname);
-
-	/* check at least one arg for least & greatest */
-	if (PGBENCH_FUNCTIONS[fnumber].nargs == -1 &&
-		elist_length(args) == 0)
-		expr_yyerror_more(yyscanner, "at least one argument expected",
-						  PGBENCH_FUNCTIONS[fnumber].fname);
-	/* special case: case (when ... then ...)+ (else ...)? end */
-	if (PGBENCH_FUNCTIONS[fnumber].nargs == -2)
-	{
-		int len = elist_length(args);
-
-		/* 'else' branch is always present, but could be a NULL-constant */
-		if (len < 3 || len % 2 != 1)
-			expr_yyerror_more(yyscanner, "odd and >= 3 number of arguments expected",
-							  "case control structure");
+	/* validate arguments number including few special cases */
+	switch (PGBENCH_FUNCTIONS[fnumber].nargs)
+	{
+		/* check at least one arg for least & greatest */
+		case PGBENCH_NARGS_VARIABLE:
+			if (len == 0)
+				expr_yyerror_more(yyscanner, "at least one argument expected",
+								  PGBENCH_FUNCTIONS[fnumber].fname);
+			break;
+
+		/* case (when ... then ...)+ (else ...)? end */
+		case PGBENCH_NARGS_CASE:
+			/* 'else' branch is always present, but could be a NULL-constant */
+			if (len < 3 || len % 2 != 1)
+				expr_yyerror_more(yyscanner,
+								  "odd and >= 3 number of arguments expected",
+								  "case control structure");
+			break;
+
+		/* hash functions with optional seed argument */
+		case PGBENCH_NARGS_HASH:
+			if (len > 2)
+				expr_yyerror_more(yyscanner, "unexpected number of arguments",
+								  PGBENCH_FUNCTIONS[fnumber].fname);
+
+			if (len == 1)
+			{
+				PgBenchExpr *var = make_variable("default_seed");
+				args = make_elist(var, args);
+			}
+			break;
+
+		/* common case: positive arguments number */
+		default:
+			Assert(PGBENCH_FUNCTIONS[fnumber].nargs >= 0);
+
+			if (PGBENCH_FUNCTIONS[fnumber].nargs != len)
+				expr_yyerror_more(yyscanner, "unexpected number of arguments",
+								  PGBENCH_FUNCTIONS[fnumber].fname);
 	}
 
 	expr->etype = ENODE_FUNCTION;

src/bin/pgbench/pgbench.c

@@ -60,6 +60,14 @@
 
 #define ERRCODE_UNDEFINED_TABLE  "42P01"
 
+/*
+ * Hashing constants
+ */
+#define FNV_PRIME 0x100000001b3
+#define FNV_OFFSET_BASIS 0xcbf29ce484222325
+#define MM2_MUL 0xc6a4a7935bd1e995
+#define MM2_ROT 47
+
 /*
  * Multi-platform pthread implementations
  */
@@ -915,6 +923,54 @@ getZipfianRand(TState *thread, int64 min, int64 max, double s)
 					  : computeHarmonicZipfian(thread, n, s));
 }
 
+/*
+ * FNV-1a hash function
+ */
+static int64
+getHashFnv1a(int64 val, uint64 seed)
+{
+	int64	result;
+	int		i;
+
+	result = FNV_OFFSET_BASIS ^ seed;
+	for (i = 0; i < 8; ++i)
+	{
+		int32 octet = val & 0xff;
+
+		val = val >> 8;
+		result = result ^ octet;
+		result = result * FNV_PRIME;
+	}
+
+	return result;
+}
+
+/*
+ * Murmur2 hash function
+ *
+ * Based on original work of Austin Appleby
+ * https://github.com/aappleby/smhasher/blob/master/src/MurmurHash2.cpp
+ */
+static int64
+getHashMurmur2(int64 val, uint64 seed)
+{
+	uint64	result = seed ^ (sizeof(int64) * MM2_MUL);
+	uint64	k = (uint64) val;
+
+	k *= MM2_MUL;
+	k ^= k >> MM2_ROT;
+	k *= MM2_MUL;
+
+	result ^= k;
+	result *= MM2_MUL;
+
+	result ^= result >> MM2_ROT;
+	result *= MM2_MUL;
+	result ^= result >> MM2_ROT;
+
+	return (int64) result;
+}
+
 /*
  * Initialize the given SimpleStats struct to all zeroes
  */
@@ -2211,6 +2267,30 @@ evalStandardFunc(TState *thread, CState *st,
 				return true;
 			}
 
+			/* hashing */
+		case PGBENCH_HASH_FNV1A:
+		case PGBENCH_HASH_MURMUR2:
+			{
+				int64	val,
+						seed;
+
+				Assert(nargs == 2);
+
+				if (!coerceToInt(&vargs[0], &val) ||
+					!coerceToInt(&vargs[1], &seed))
+					return false;
+
+				if (func == PGBENCH_HASH_MURMUR2)
+					setIntValue(retval, getHashMurmur2(val, seed));
+				else if (func == PGBENCH_HASH_FNV1A)
+					setIntValue(retval, getHashFnv1a(val, seed));
+				else
+					/* cannot get here */
+					Assert(0);
+
+				return true;
+			}
+
 		default:
 			/* cannot get here */
 			Assert(0);
@@ -4963,6 +5043,10 @@ main(int argc, char **argv)
 		exit(1);
 	}
 
+	/* set random seed */
+	INSTR_TIME_SET_CURRENT(start_time);
+	srandom((unsigned int) INSTR_TIME_GET_MICROSEC(start_time));
+
 	if (internal_script_used)
 	{
 		/*
@@ -5024,6 +5108,19 @@ main(int argc, char **argv)
 		}
 	}
 
+	/* set default seed for hash functions */
+	if (lookupVariable(&state[0], "default_seed") == NULL)
+	{
+		uint64	seed = ((uint64) (random() & 0xFFFF) << 48) |
+					   ((uint64) (random() & 0xFFFF) << 32) |
+					   ((uint64) (random() & 0xFFFF) << 16) |
+					   (uint64) (random() & 0xFFFF);
+
+		for (i = 0; i < nclients; i++)
+			if (!putVariableInt(&state[i], "startup", "default_seed", (int64) seed))
+				exit(1);
+	}
+
 	if (!is_no_vacuum)
 	{
 		fprintf(stderr, "starting vacuum...");
@@ -5041,10 +5138,6 @@ main(int argc, char **argv)
 	}
 	PQfinish(con);
 
-	/* set random seed */
-	INSTR_TIME_SET_CURRENT(start_time);
-	srandom((unsigned int) INSTR_TIME_GET_MICROSEC(start_time));
-
 	/* set up thread data structures */
 	threads = (TState *) pg_malloc(sizeof(TState) * nthreads);
 	nclients_dealt = 0;

src/bin/pgbench/pgbench.h

@@ -97,7 +97,9 @@ typedef enum PgBenchFunction
 	PGBENCH_LE,
 	PGBENCH_LT,
 	PGBENCH_IS,
-	PGBENCH_CASE
+	PGBENCH_CASE,
+	PGBENCH_HASH_FNV1A,
+	PGBENCH_HASH_MURMUR2
 } PgBenchFunction;
 
 typedef struct PgBenchExpr PgBenchExpr;