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commit    89f2b64da370e7b0737760e3282f096591d6518f
Author:   Noah Misch <noah@leadboat.com>
Date:     Mon Sep 24 05:56:39 2018 +0000
First released in: 12.0, 9.3.25, 9.4.20, 9.5.15, 9.6.11, 10.6, 11.0

    Initialize random() in bootstrap/stand-alone postgres and in initdb.
    
    This removes a difference between the standard IsUnderPostmaster
    execution environment and that of --boot and --single.  In a stand-alone
    backend, "SELECT random()" always started at the same seed.
    
    On a system capable of using posix shared memory, initdb could still
    conclude "selecting dynamic shared memory implementation ... sysv".
    Crashed --boot or --single postgres processes orphaned shared memory
    objects having names that collided with the not-actually-random names
    that initdb probed.  The sysv fallback appeared after ten crashes of
    --boot or --single postgres.  Since --boot and --single are rare in
    production use, systems used for PostgreSQL development are the
    principal candidate to notice this symptom.
    
    Back-patch to 9.3 (all supported versions).  PostgreSQL 9.4 introduced
    dynamic shared memory, but 9.3 does share the "SELECT random()" problem.
    
    Reviewed by Tom Lane and Kyotaro HORIGUCHI.
    
    Discussion: https://postgr.es/m/20180915221546.GA3159382@rfd.leadboat.com


 src/backend/utils/init/miscinit.c | 8 ++++++++
 src/bin/initdb/initdb.c           | 3 +++
 2 files changed, 11 insertions(+)

diff --git a/src/backend/utils/init/miscinit.c b/src/backend/utils/init/miscinit.c
index 03b28c3604a..98c2c1949d4 100644
--- a/src/backend/utils/init/miscinit.c
+++ b/src/backend/utils/init/miscinit.c
@@ -320,6 +320,14 @@ InitStandaloneProcess(const char *argv0)
 
 	MyStartTime = time(NULL);	/* set our start time in case we call elog */
 
+	/*
+	 * Initialize random() for the first time, like PostmasterMain() would.
+	 * In a regular IsUnderPostmaster backend, BackendRun() computes a
+	 * high-entropy seed before any user query.  Fewer distinct initial seeds
+	 * can occur here.
+	 */
+	srandom((unsigned int) (MyProcPid ^ MyStartTime));
+
 	/* Initialize process-local latch support */
 	InitializeLatchSupport();
 	MyLatch = &LocalLatchData;
diff --git a/src/bin/initdb/initdb.c b/src/bin/initdb/initdb.c
index ae22e7d9fb8..a9bbc8985ea 100644
--- a/src/bin/initdb/initdb.c
+++ b/src/bin/initdb/initdb.c
@@ -922,6 +922,9 @@ choose_dsm_implementation(void)
 #ifdef HAVE_SHM_OPEN
 	int			ntries = 10;
 
+	/* Initialize random(); this function is its only user in this program. */
+	srandom((unsigned int) (getpid() ^ time(NULL)));
+
 	while (ntries > 0)
 	{
 		uint32		handle;


[parent: b1356f18b70e]