Tom Lane wrote:
Heikki Linnakangas <[EMAIL PROTECTED]> writes:
Tom Lane wrote:
I'd be happier if the DSM content could be
treated as just a hint.


If we don't have a frozen state, we can't use the DSM to implement index-only scans.

To implement index-only scans, the DSM would have to be expected to
provide 100% reliable coverage, which will increase its cost and
complexity by orders of magnitude.  If you insist on that, I will bet
you lunch at a fine restaurant that it doesn't make it into 8.3.

:)

While I understand that 100% reliable coverage is a significantly stronger guarantee, I don't see any particular problems in implementing that. WAL logging isn't that hard.

I won't insist, I'm not the one doing the programming after all. Anything is better than what we have now. However, I do hope that whatever is implemented doesn't need a complete rewrite to make it 100% reliable in the future.

The basic wish I have is to not use a fixed size shared memory area like FSM for the DSM. I'd like it to use the shared buffers instead, which makes the memory management and tuning easier. And it also makes it easier to get the WAL logging right, even if it's not done for 8.3 but added later.

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

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