Thread

1. replacing shmem

   V. M. <txian@hotmail.com> — 2001-01-06T03:01:58Z

   Excuse my ignorance.
   Is there a way to replace the shmem and sem (ipc.c) to use files. In this 
   way we can have a sort of a parallel server using GFS.
   1.Starting a postmaster on ONE machine creates the shared structures, 2.then 
   start on other cluster-machines, the variuos machines share the same 
   datafiles and shared memory (on-file) structures
   3.cliets connects (for example) round-robin to the clustered-postgres-nodes.
   4.a problem is proper destroy and create of the shared structures
   
   thanks,
   valter
   
   
   >From http://sistina.com/gfs/:
   
   he Global File System (GFS [now in beta4]) is a shared disk cluster file 
   system for Linux. GFS supports journaling and recovery from client failures. 
   GFS cluster
                                         nodes physically share the same 
   storage by means of Fibre Channel or shared SCSI devices. The file system 
   appears to be local on each node and GFS
                                         synchronizes file access across the 
   cluster. GFS is fully symmetric, that is, all nodes are equal and there is 
   no server which may be a bottleneck or
                                         single point of failure. GFS uses read 
   and write caching while maintaining full UNIX file system semantics.
   
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2. Re: replacing shmem

   Tom Lane <tgl@sss.pgh.pa.us> — 2001-01-06T03:52:56Z

   "Valter Mazzola" <txian@hotmail.com> writes:
   > Is there a way to replace the shmem and sem (ipc.c) to use files. In this 
   > way we can have a sort of a parallel server using GFS.
   
   Unless GFS offers access bandwidth approaching main memory speeds, this
   idea is sheer folly :-(
   
   			regards, tom lane
   
   

3. RE: replacing shmem

   Andrew Snow <als@fl.net.au> — 2001-01-06T04:02:55Z

   I suppose it won't help here to suggest using memory mapped I/O, because
   someone will complain their platform doesn't support it. I wonder though if
   there could be an optional patch to use mmap for all disk I/O, not just
   shared memory!
   
   - Andrew
   
   
   
   

4. Re: replacing shmem

   Tom Samplonius <tom@sdf.com> — 2001-01-06T04:09:29Z

   On Sat, 6 Jan 2001, Valter Mazzola wrote:
   
   > Excuse my ignorance.
   > Is there a way to replace the shmem and sem (ipc.c) to use files. In this 
   > way we can have a sort of a parallel server using GFS.
   ...
   
     Besides the slowness of file IO, it also doesn't make sense to have a
   shared memory area for all nodes.  Not all pages in the shared memory area
   are dirty pages, and it make no sense for all nodes to share the same read
   cache, when they could have individual read caches.  Besides, it is more
   scalable.
   
     Either way, an application level cluster employing two-phase commit is
   likely going to be a lot more useful.  FrontBase
   (http://www.frontbase.com) supports this now, and on more platforms than
   GFS supports.  Besides, GFS is rather alpha right now.
   
   Tom