pgbench-sampling-v2.diff

diff --git a/contrib/pgbench/pgbench.c b/contrib/pgbench/pgbench.c
index 00cab73..12c1338 100644
--- a/contrib/pgbench/pgbench.c
+++ b/contrib/pgbench/pgbench.c
@@ -145,6 +145,9 @@ char	   *index_tablespace = NULL;
 #define naccounts	100000
 
 bool		use_log;			/* log transaction latencies to a file */
+bool		use_log_sampling;	/* sample the log randomly */
+int			nsample_rate = 100;	/* default log sampling rate */
+
 bool		is_connect;			/* establish connection for each transaction */
 bool		is_latencies;		/* report per-command latencies */
 int			main_pid;			/* main process id used in log filename */
@@ -364,6 +367,7 @@ usage(void)
 		   "  -f FILENAME  read transaction script from FILENAME\n"
 		   "  -j NUM       number of threads (default: 1)\n"
 		   "  -l           write transaction times to log file\n"
+		   "  -R NUM       log sampling rate in pct (default: 100)\n"
 		   "  -M simple|extended|prepared\n"
 		   "               protocol for submitting queries to server (default: simple)\n"
 		   "  -n           do not run VACUUM before tests\n"
@@ -877,21 +881,25 @@ top:
 			instr_time	diff;
 			double		usec;
 
-			INSTR_TIME_SET_CURRENT(now);
-			diff = now;
-			INSTR_TIME_SUBTRACT(diff, st->txn_begin);
-			usec = (double) INSTR_TIME_GET_MICROSEC(diff);
+			/* either no sampling or is within the sample */
+			if ((! use_log_sampling) || (getrand(thread, 0, 99) < nsample_rate)) {
+
+				INSTR_TIME_SET_CURRENT(now);
+				diff = now;
+				INSTR_TIME_SUBTRACT(diff, st->txn_begin);
+				usec = (double) INSTR_TIME_GET_MICROSEC(diff);
 
 #ifndef WIN32
-			/* This is more than we really ought to know about instr_time */
-			fprintf(logfile, "%d %d %.0f %d %ld %ld\n",
-					st->id, st->cnt, usec, st->use_file,
-					(long) now.tv_sec, (long) now.tv_usec);
+				/* This is more than we really ought to know about instr_time */
+				fprintf(logfile, "%d %d %.0f %d %ld %ld\n",
+						st->id, st->cnt, usec, st->use_file,
+						(long) now.tv_sec, (long) now.tv_usec);
 #else
-			/* On Windows, instr_time doesn't provide a timestamp anyway */
-			fprintf(logfile, "%d %d %.0f %d 0 0\n",
-					st->id, st->cnt, usec, st->use_file);
+				/* On Windows, instr_time doesn't provide a timestamp anyway */
+				fprintf(logfile, "%d %d %.0f %d 0 0\n",
+						st->id, st->cnt, usec, st->use_file);
 #endif
+			}
 		}
 
 		if (commands[st->state]->type == SQL_COMMAND)
@@ -1962,7 +1970,7 @@ main(int argc, char **argv)
 	state = (CState *) xmalloc(sizeof(CState));
 	memset(state, 0, sizeof(CState));
 
-	while ((c = getopt_long(argc, argv, "ih:nvp:dSNc:j:Crs:t:T:U:lf:D:F:M:", long_options, &optindex)) != -1)
+	while ((c = getopt_long(argc, argv, "ih:nvp:dSNc:j:Crs:t:T:U:lf:R:D:F:M:", long_options, &optindex)) != -1)
 	{
 		switch (c)
 		{
@@ -2070,6 +2078,15 @@ main(int argc, char **argv)
 			case 'l':
 				use_log = true;
 				break;
+			case 'R':
+				use_log_sampling = true;
+				nsample_rate = atoi(optarg);
+				if (nsample_rate <= 0 || nsample_rate > 100)
+				{
+					fprintf(stderr, "invalid sampling rate: %d\n", nsample_rate);
+					exit(1);
+				}
+				break;
 			case 'f':
 				ttype = 3;
 				filename = optarg;
@@ -2158,6 +2175,12 @@ main(int argc, char **argv)
 		exit(1);
 	}
 
+	/* -R may be used only with -l */
+	if (use_log_sampling && (! use_log)) {
+		fprintf(stderr, "log sampling rate is allowed only when logging transactions\n");
+		exit(1);
+	}
+
 	/*
 	 * is_latencies only works with multiple threads in thread-based
 	 * implementations, not fork-based ones, because it supposes that the
diff --git a/doc/src/sgml/pgbench.sgml b/doc/src/sgml/pgbench.sgml
index 437fcea..962e446 100644
--- a/doc/src/sgml/pgbench.sgml
+++ b/doc/src/sgml/pgbench.sgml
@@ -317,6 +317,22 @@ pgbench <optional> <replaceable>options</> </optional> <replaceable>dbname</>
      </varlistentry>
 
      <varlistentry>
+      <term><option>-R</option> <replaceable>rate</></term>
+      <listitem>
+       <para>
+        Sampling rate, used when writing data into the log in percent. 100 means all
+        transactions will be logged, 1 means only 1% of the transactions will be logged.
+        Default is 100 (all transactions).
+       </para>
+       <para>
+        Be careful when processing the log file - e.g. when computing tps values, you
+        need to multiply the numbers accordingly (e.g. with 1% sample you'll get 1/100
+        of the actual tps).
+       </para>
+      </listitem>
+     </varlistentry>
+
+     <varlistentry>
       <term><option>-M</option> <replaceable>querymode</></term>
       <listitem>
        <para>