Re: postgresql cluster on SAN

Spiegelberg, Greg wrote:

>This is possible.  Below is a brief recipe.
>
>1. Use Veritas Storage Foundation HA with Cluster File System.
>2. Have a volume with cfs available to 2 or more systems via SAN.
>3. Install PostgreSQL and be sure PGDATA is on the cfs mount
>4. Create a Storage Checkpoint of cfs mount (read-write virtual copy)
>5. Bring up PostgreSQL on node1
>6. Mount storage checkpoint on node2
>7. Start PostgreSQL on node2
>
>Drawbacks?  Heck yes.  There are many and you should understand the
>nature of Veritas Storage Checkpoints before using.
>
Drawback #1-- only works read-only on all but one node.  And I am not
even sure what will happen when you start writing on that one node...

>  I have tested it
>though in conjunction with dblink() and some other proprietary API's we
>use for load balancing and the potential is there to manage many large
>SELECT's.
>
>
Ok, but what happens when you start doing inserts, updates, and deletes.

Somehow I think that PostgreSQL's dependance on shmem and semaphores
will cause corruption in your database as soon as you start writing to
it on both nodes.  And I don't know enough about PostgreSQL's internal
structure to know if writing on only one node is safe.

Best Wishes,
Chris Travers
Metatron Technology Consulting