From 329cacb902705c44c66098535c61f8e84f6f6ee0 Mon Sep 17 00:00:00 2001 From: Noah Misch Date: Sun, 23 Sep 2018 22:56:39 -0700 Subject: [PATCH] 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 d4625a6238..b93beb7699 100644 --- a/src/backend/utils/init/miscinit.c +++ b/src/backend/utils/init/miscinit.c @@ -223,6 +223,14 @@ 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 d758a5d596..66e3c84eb5 100644 --- a/src/bin/initdb/initdb.c +++ b/src/bin/initdb/initdb.c @@ -1058,6 +1058,9 @@ 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;