On 06/04/2015 12:17 PM, Andres Freund wrote:
On 2015-06-04 11:51:44 +0300, Heikki Linnakangas wrote:
So, I'm all for refactoring and adding abstractions where it makes sense,
but it's not going to solve design problems.

I personally don't really see the multixact changes being that bad on
the overall design. It pretty much just extended an earlier design. Now
that wasn't great, but I don't think too many people had realized that
at that point.  The biggest problem was underestimating the complexity.

Yeah, many of the issues were pre-existing, and would've been good to fix anyway.

The multixact issues remind me of the another similar thing we did: the visibility map. It too was non-critical when it was first introduced, but later we started using it for index-only-scans, and it suddenly became important that it's up-to-date and crash-safe. We did uncover some bugs in that area when index-only-scans were introduced, similar to the multixact bugs, only not as bad because it didn't lead to data loss. I don't have any point to make with that comparison, but it was similar in many ways.

- Heikki



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