XOR process PID into a backend's initial random seed, to ensure that

tglsfdc · tglsfdc · commit 52a45818a13b · 2004-10-07T00:03:15.000Z
different backends get a reasonably wide set of initial seeds even if
gettimeofday returns tv_usec values with only a few bits of precision.
Per recent discussion.
diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c
@@ -37,7 +37,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/postmaster/postmaster.c,v 1.426 2004/10/06 09:35:21 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/postmaster/postmaster.c,v 1.427 2004/10/07 00:03:15 tgl Exp $
  *
  * NOTES
  *
@@ -2575,8 +2575,6 @@ static int
 BackendRun(Port *port)
 {
 	int			status;
-	struct timeval now;
-	struct timezone tz;
 	char		remote_host[NI_MAXHOST];
 	char		remote_port[NI_MAXSERV];
 	char		remote_ps_data[NI_MAXHOST];
@@ -2754,9 +2752,7 @@ BackendRun(Port *port)
 	 * start a new random sequence in the random() library function.
 	 */
 	random_seed = 0;
-	gettimeofday(&now, &tz);
-	srandom((unsigned int) now.tv_usec);
-
+	srandom((unsigned int) (MyProcPid ^ port->session_start.tv_usec));
 
 	/* ----------------
 	 * Now, build the argv vector that will be given to PostgresMain.

Original file line number	Diff line number	Diff line change
`@@ -37,7 +37,7 @@`
`37`	`37`	`*`
`38`	`38`	`*`
`39`	`39`	`* IDENTIFICATION`
`40`		`- * $PostgreSQL: pgsql/src/backend/postmaster/postmaster.c,v 1.426 2004/10/06 09:35:21 momjian Exp $`
	`40`	`+ * $PostgreSQL: pgsql/src/backend/postmaster/postmaster.c,v 1.427 2004/10/07 00:03:15 tgl Exp $`
`41`	`41`	`*`
`42`	`42`	`* NOTES`
`43`	`43`	`*`
`@@ -2575,8 +2575,6 @@ static int`
`2575`	`2575`	`BackendRun(Port *port)`
`2576`	`2576`	`{`
`2577`	`2577`	`int status;`
`2578`		`- struct timeval now;`
`2579`		`- struct timezone tz;`
`2580`	`2578`	`char remote_host[NI_MAXHOST];`
`2581`	`2579`	`char remote_port[NI_MAXSERV];`
`2582`	`2580`	`char remote_ps_data[NI_MAXHOST];`
`@@ -2754,9 +2752,7 @@ BackendRun(Port *port)`
`2754`	`2752`	`* start a new random sequence in the random() library function.`
`2755`	`2753`	`*/`
`2756`	`2754`	`random_seed = 0;`
`2757`		`- gettimeofday(&now, &tz);`
`2758`		`- srandom((unsigned int) now.tv_usec);`
`2759`		`-`
	`2755`	`+ srandom((unsigned int) (MyProcPid ^ port->session_start.tv_usec));`
`2760`	`2756`
`2761`	`2757`	`/* ----------------`
`2762`	`2758`	`* Now, build the argv vector that will be given to PostgresMain.`