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

diff --git a/src/backend/utils/init/miscinit.c b/src/backend/utils/init/miscinit.c
index 865119d272935959f666f234b7d2170dc504f437..f590ecb25e87f0e2c1813148fe1cee37ccea71b7 100644 (file)
--- a/src/backend/utils/init/miscinit.c
+++ b/src/backend/utils/init/miscinit.c
@@ -325,6 +325,14 @@ 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 cb8c7450d9bc1d4c53a9bae390de28b2f27ffb34..e155c6ae2fcb6f25612f0147449e0454dd062343 100644 (file)
--- a/src/bin/initdb/initdb.c
+++ b/src/bin/initdb/initdb.c
@@ -923,6 +923,9 @@ 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;