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Fix broken mmap failure-detection code, and improve error message.

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Per an observation by Thom Brown that my previous commit made an
overly large shmem allocation crash the server, on Linux.
This commit is contained in:
Robert Haas 2012-06-28 12:57:22 -04:00
parent b0fc0df936
commit 39715af23a
1 changed files with 10 additions and 3 deletions
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13
src/backend/port/sysv_shmem.c
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@ -419,10 +419,17 @@ PGSharedMemoryCreate(Size size, bool makePrivate, int port)
*/
AnonymousShmem = mmap(NULL, size, PROT_READ|PROT_WRITE, PG_MMAP_FLAGS,
-1, 0);
if (AnonymousShmem == NULL)
if (AnonymousShmem == MAP_FAILED)
ereport(FATAL,
(errmsg("could not map %lu bytes of anonymous shared memory: %m",
(unsigned long) AnonymousShmemSize)));
(errmsg("could not map anonymous shared memory: %m"),
(errno == ENOMEM) ?
errhint("This error usually means that PostgreSQL's request "
"for a shared memory segment exceeded available memory "
"or swap space. To reduce the request size (currently "
"%lu bytes), reduce PostgreSQL's shared memory usage, "
"perhaps by reducing shared_buffers or "
"max_connections.",
(unsigned long) AnonymousShmemSize) : 0));
/* Now we can allocate a minimal SHM block. */
allocsize = sizeof(PGShmemHeader);