Hello Fabien,
17/01/2018 10:52, Fabien COELHO пишет:
>> Here is a new version of patch. I've splitted it into two parts. The
>> first one is almost the same as v4 from [1] with some refactoring.
>> The second part introduces random_seed variable as you proposed.
>
> Patch 1 applies. Compilations fails, there are two "hash_seed"
> declared in "pgbench.c".
>
> Patch 2 applies cleanly on top of the previous patch and compiles,
> because the variable is removed...
>
> If an ":hash_seed" pgbench variable is used, ISTM that there is no
> need for a global variable at all, so the two patches are going back
> and forth, which is unhelpful. ISTM better to provide just one
> combined patch for the feature.
>
> If the hash_seed variable really needs to be kept, it should be an
> "int64" variable, like other pgbench values.
>
> The len < 1 || len > 2 is checked twice, once in the "switch", on in
> an "if" just after the "switch". Once is enough.
I totally messed up doing git rebase and didn't double check the code.
*facepalm* There shouldn't be hash_seed variable and the second 'len < 1
|| len > 2' check. Sorry for that, fixed in the attached patch.
> Calling random just usually initializes about 31 bits, so random
> should be called 2 or maybe 3 times? Or maybe use the internal getrand
> which has 48 pseudorandom bits?
Done. I used code from get_random_uint64() as an example.
>
> For me "random seed" is what is passed to srandom, so the variable
> should rather be named hash_seed because there could also be a random
> seed (actually, there is in another parallel patch:-). Moreover, this
> seed may or may not be random if set, so calling it "random_seed" is
> not desirable.
>
My intention was to introduce seed variable which potentially could be
used in different contexts, not only for hash functions. I renamed it to
'hash_seed' for now. But what do you think about naming it simply 'seed'
or choosing some other general name?
>> I didn't do the executor simplification thing yet because I'm a
>> little concerned about inventive users, who may want to change
>> random_seed variable in runtime (which is possible since pgbench
>> doesn't have read only variables aka constants AFAIK).
>
> If the user choses to overide hash_seed in their script, it is their
> decision, the documentation has only to be clear about :hash_seed
> being the default seed. I see no clear reason to work around this
> possibility by evaluating the seed at parse time, especially as the
> variable may not have its final value yet depending on the option
> order. I'd suggest to just use make_variable("hash_seed") for the
> default second argument and simplify the executor.
That is a great idea, I didn't see that possibility. Done.
>
> The seed variable is not tested explicitely in the script, you could add
> a "hash(5432) == hash(5432, :hash_seed)" for instance.
>
> It would be nice if an native English speaker could proofread the
> documentation text. I'd suggest: "*an* optional seed parameter". "In
> case *the* seed...". "<literal>:hash_seed</literal>". "shared for" ->
> "shared by". "following listing" -> "following pgbench script". "few
> accounts generates" -> "few accounts generate".
>
Done as well.
> For the document example, I'd use larger values for the random &
> modulo, eg 100000000 and 1000000. The drawback is that zipfian does a
> costly computation of the generalized harmonic number when the
> parameter is lower than 1.0. For cities, the parameter found by Zipf
> was 1.07 (says Wikipedia). Maybe use this historical value. Or maybe
> use an exponential distribution in the example.
>
Changed parameter to 1.07.
Thanks!
--
Ildar Musin
Postgres Professional: http://www.postgrespro.com
Russian Postgres Company
diff --git a/doc/src/sgml/ref/pgbench.sgml b/doc/src/sgml/ref/pgbench.sgml
index 3dd492c..c31254c 100644
--- a/doc/src/sgml/ref/pgbench.sgml
+++ b/doc/src/sgml/ref/pgbench.sgml
@@ -882,6 +882,11 @@ pgbench <optional> <replaceable>options</replaceable>
</optional> <replaceable>d
<entry> <literal>client_id</literal> </entry>
<entry>unique number identifying the client session (starts from
zero)</entry>
</row>
+
+ <row>
+ <entry> <literal>hash_seed</literal> </entry>
+ <entry>random seed used in hash functions by default</entry>
+ </row>
</tbody>
</tgroup>
</table>
@@ -1246,6 +1251,27 @@ pgbench <optional> <replaceable>options</replaceable>
</optional> <replaceable>d
<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><literal>FNV</literal> hash</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><literal>murmur2</literal> hash</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>
<entry>cast to int</entry>
@@ -1423,6 +1449,22 @@ f(x) = PHI(2.0 * parameter * (x - mu) / (max - min + 1))
/
</itemizedlist>
<para>
+ Hash functions accepts an input value and an optional seed parameter. In
case the seed isn't provided <literal>hash_seed</literal> value is used. Hash
functions can be used, for example, to modify the distribution of
<literal>random_zipfian</literal> or <literal>random_exponential</literal>
functions in order to obtain scattered distribution. Thus 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), :hash_seed + 123) % 1000000
+\set k2 abs(hash(:r), :hash_seed + 321) % 1000000
+</programlisting>
+ </para>
+
+ <para>
As an example, the full definition of the built-in TPC-B-like
transaction is:
diff --git a/src/bin/pgbench/exprparse.y b/src/bin/pgbench/exprparse.y
index e23ca51..b5e150f 100644
--- a/src/bin/pgbench/exprparse.y
+++ b/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", -3, PGBENCH_HASH_MURMUR2
+ },
+ {
+ "hash_murmur2", -3, PGBENCH_HASH_MURMUR2
+ },
+ {
+ "hash_fnv1a", -3, PGBENCH_HASH_FNV1A
},
/* keep as last array element */
{
@@ -423,29 +449,49 @@ 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("hash_seed");
+ args = make_elist(var, args);
+ }
+ break;
+
+ /* common case: positive arguments number */
+ default:
+ if (PGBENCH_FUNCTIONS[fnumber].nargs != len)
+ expr_yyerror_more(yyscanner, "unexpected number
of arguments",
+
PGBENCH_FUNCTIONS[fnumber].fname);
}
expr->etype = ENODE_FUNCTION;
diff --git a/src/bin/pgbench/pgbench.c b/src/bin/pgbench/pgbench.c
index 31ea6ca..8e6e0ad 100644
--- a/src/bin/pgbench/pgbench.c
+++ b/src/bin/pgbench/pgbench.c
@@ -61,6 +61,14 @@
#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 +923,51 @@ getZipfianRand(TState *thread, int64 min, int64 max,
double 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
+ */
+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
*/
static void
@@ -2209,6 +2262,28 @@ evalStandardFunc(
return true;
}
+ /* hashing */
+ case PGBENCH_HASH_FNV1A:
+ case PGBENCH_HASH_MURMUR2:
+ {
+ int64 val;
+ int64 seed;
+ int64 result;
+
+ Assert(nargs == 2);
+
+ if (!coerceToInt(&vargs[0], &val))
+ return false;
+
+ if (!coerceToInt(&vargs[1], &seed))
+ return false;
+
+ result = (func == PGBENCH_HASH_FNV1A) ?
+ getHashFnv1a(val, seed) :
getHashMurmur2(val, seed);
+ setIntValue(retval, result);
+ return true;
+ }
+
default:
/* cannot get here */
Assert(0);
@@ -4972,6 +5047,10 @@ 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)
{
/*
@@ -5033,6 +5112,21 @@ main(int argc, char **argv)
}
}
+ /* set default seed for hash functions */
+ if (lookupVariable(&state[0], "hash_seed") == NULL)
+ {
+ uint64 seed;
+
+ seed = (uint64) (random() & 0xFFFF) << 48;
+ seed |= (uint64) (random() & 0xFFFF) << 32;
+ seed |= (uint64) (random() & 0xFFFF) << 16;
+ seed |= (uint64) (random() & 0xFFFF);
+
+ for (i = 0; i < nclients; i++)
+ if (!putVariableInt(&state[i], "startup", "hash_seed",
(int64) seed))
+ exit(1);
+ }
+
if (!is_no_vacuum)
{
fprintf(stderr, "starting vacuum...");
@@ -5050,10 +5144,6 @@ 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;
diff --git a/src/bin/pgbench/pgbench.h b/src/bin/pgbench/pgbench.h
index 0705ccd..6983865 100644
--- a/src/bin/pgbench/pgbench.h
+++ b/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;
diff --git a/src/bin/pgbench/t/001_pgbench_with_server.pl
b/src/bin/pgbench/t/001_pgbench_with_server.pl
index a8b2962..752c299 100644
--- a/src/bin/pgbench/t/001_pgbench_with_server.pl
+++ b/src/bin/pgbench/t/001_pgbench_with_server.pl
@@ -259,6 +259,11 @@ pgbench(
qr{command=46.: int 46\b},
qr{command=47.: boolean true\b},
qr{command=48.: boolean true\b},
+ qr{command=49.: int -5817877081768721676\b},
+ qr{command=50.: boolean true\b},
+ qr{command=51.: int -7793829335365542153\b},
+ qr{command=52.: int -?\d+\b},
+ qr{command=53.: boolean true\b},
],
'pgbench expressions',
{ '001_pgbench_expressions' => q{-- integer functions
@@ -327,6 +332,12 @@ pgbench(
\set n6 debug(:n IS NULL AND NOT :f AND :t)
-- conditional truth
\set cs debug(CASE WHEN 1 THEN TRUE END AND CASE WHEN 1.0 THEN TRUE END AND
CASE WHEN :n THEN NULL ELSE TRUE END)
+-- hash functions
+\set h0 debug(hash(10, 5432))
+\set h1 debug(:h0 = hash_murmur2(10, 5432))
+\set h3 debug(hash_fnv1a(10, 5432))
+\set h4 debug(hash(10))
+\set h5 debug(hash(10) = hash(10, :hash_seed))
-- lazy evaluation
\set zy 0
\set yz debug(case when :zy = 0 then -1 else (1 / :zy) end)
