On 29.10.2010 06:00, Jeff Janes wrote:
One of the items on the Wiki ToDo list is sorted writes for checkpoints. The consensus seemed to be that this should be done by adding hook(s) into the main code, and then a contrib module to work with those hooks. Is there an existing contrib module that one could best look to for inspiration on how to go about doing this? I have the sorted checkpoint working under a guc, but don't know where to start on converting it to a contrib module instead.
I don't think it's a good idea to have this as a hook. Bgwriter shouldn't need to load external code, and checkpoint robustness should dependend on user-written code. IIRC Tom Lane didn't even like pallocing the memory for the list of dirty pages at checkpoint time because that might cause an out-of-memory error. Calling a function in a contrib module is much much worse.
Simon's argument in the thread that the todo item points to (http://archives.postgresql.org/pgsql-patches/2008-07/msg00123.php) is basically that we don't know what the best algorithm is yet and benchmarking is a lot of work, so let's just let people do whatever they feel like until we settle on the best approach. I think we need to bite the bullet and do some benchmarking, and commit one carefully vetted patch to the backend.
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