Re: Re: [PATCHES] PostgreSQL virtual hosting support

> I was afraid you were planning to run that way. Did you absorb the
> point about shared memory keys being based (only) on the port number?
> Unless something's done about that, the above configuration will NOT
> work, because the different instances will try to use the same
> shared memory and semaphore sets.

Yes, my patch addresses that issue, as well as I could figure out to do.
Here's part of the code I submitted in postmaster.c:

/*
+ * get_host_port -- return a pseudo port number (16 bits)
+ * derived from the primary IP address of HostName.
+ */
+ static unsigned short
+ get_host_port(void)
+ {
+ static unsigned short hostPort = 0;
+
+ if (hostPort == 0)
+ {
+ SockAddr saddr;
+ struct hostent *hp;
+
+ hp = gethostbyname(HostName);
+ if ((hp == NULL) || (hp->h_addrtype != AF_INET))
+ {
+ char msg[1024];
+ snprintf(msg, sizeof(msg),
+ "FATAL: get_host_port: gethostbyname(%s) failed: %s\n",
+ HostName, hstrerror(h_errno));
+ fputs(msg, stderr);
+ pqdebug("%s", msg);
+ exit(1);
+ }
+ memmove((char *) &(saddr.in.sin_addr),
+ (char *) hp->h_addr,
+ hp->h_length);
+ hostPort = ntohl(saddr.in.sin_addr.s_addr) & 0xFFFF;
+ }
+
+ return hostPort;
+ }
+
+ /*
* reset_shared -- reset shared memory and semaphores
*/
static void
reset_shared(unsigned short port)
{
+ /*
+ * A typical ipc_key is 5432001, which is port 5432, sequence
+ * number 0, and 01 as the index in IPCKeyGetBufferMemoryKey().
+ * The 32-bit INT_MAX is 2147483 6 47.
+ *
+ * The default algorithm for calculating the IPC keys assumes that all
+ * instances of postmaster on a given host are listening on different
+ * ports. In order to work (prevent shared memory collisions) if you
+ * run multiple PostgreSQL instances on the same port and different IP
+ * addresses on a host, we change the algorithm if you give postmaster
+ * the -h option, or set PGHOST, to a value other than the internal
+ * default of "any".
+ *
+ * If HostName is not "any", then we generate the IPC keys using the
+ * last two octets of the IP address instead of the port number.
+ * This algorithm assumes that no one will run multiple PostgreSQL
+ * instances on one host using two IP addresses that have the same two
+ * last octets in different class C networks. If anyone does, it
+ * would be rare.
+ *
+ * So, if you use -h or PGHOST, don't try to run two instances of
+ * PostgreSQL on the same IP address but different ports. If you
+ * don't use them, then you must use different ports (via -p or
+ * PGPORT). And, of course, don't try to use both approaches on one
+ * host.
+ */
+
+ if (strcmp(HostName, "any"))
+ port = get_host_port();
+
ipc_key = port * 1000 + shmem_seq * 100;
CreateSharedMemoryAndSemaphores(ipc_key, MaxBackends);