On 23.02.2011 03:00, Joachim Wieland wrote:
On Tue, Feb 22, 2011 at 3:34 PM, Heikki Linnakangas
<heikki.linnakan...@enterprisedb.com>  wrote:
Yes, that's the point I was trying to make. I believe the idea of a hash was
that it takes less memory than storing the whole snapshot (and more
importantly, a fixed amount of memory per snapshot). But I'm not convinced
either that dealing with a hash is any less troublesome.

Both Tom and Robert voted quite explicitly against the
store-in-shared-memory idea. Others don't want to allow people request
arbitrary snapshots and again others wanted to pass the snapshot
through the client so that in the future we could also request
snapshots from standby servers. The hash idea seemed to at least make
nobody unhappy.

For easier review, here are a few links to the previous discusion:


Why exactly, Heikki do you think the hash is more troublesome?

It just feels wrong to rely on cryptography just to save some shared memory.

I realize that there are conflicting opinions on this, but from user point-of-view the hash is just a variant of the idea of passing the snapshot through shared memory, just implemented in an indirect way.

And how
could we validate/invalidate snapshots without the checksum (assuming
the through-the-client approach instead of storing the whole snapshot
in shared memory)?

Either you accept anything that passes sanity checks, or you store the whole snapshot in shared memory (or a temp file). I'm not sure which is better, but they both seem better than the hash.

  Heikki Linnakangas
  EnterpriseDB   http://www.enterprisedb.com

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