On Thu, Jul 14, 2005 at 11:30:36AM -0500, Jim C. Nasby wrote: > On Wed, Jul 13, 2005 at 07:52:04PM -0400, Bruce Momjian wrote: > > This is a good point. We have always stored data on disk that exactly > > matches its layout in memory. We could change that, but no one has > > shown it would be a win. > > Out of curiosity, what would be involved in hacking the backend enough > to be able to test this theory out? I'm guessing you'd want to convert > between on-disk and in-memory formats as you read pages in, so either > on-disk pages would become variable size (and smaller than memory pages) > or in-memory pages would become variable size (and larger than on-disk > pages). It's a pain because on some architectures you can't do unaligned accesses. I imagine you'd have to have the on-disk pages in memory and copy them to a temporary space when you actually want to use the data, converting on the fly. IMHO a much much better approach would be the two phase: - Decouple order of columns on disk from logical column order Then people can rearrange columns, people do ask that occasionally. - Change CREATE TABLE to rearrange columns on disk (not the logical order) to minimize padding. This gives you real benefits without having to overhaul the code... > On a side note, I think it might be useful to have a seperate TODO > catagory for ideas that need to be tested to see if they're worth > implementing for real. This is a case where it's probably substantially > easier to estimate (or maybe even measure) how much there is to gain > from this than to do the actual work and then see if it helps. It's also > likely that a less experienced hacker could test the theory out. Some > likely items for this list: What usually happens is someone tries it and it either works or it doesn't... Can't comment on the other ideas. Have a nice day, -- Martijn van Oosterhout <kleptog@xxxxxxxxx> http://svana.org/kleptog/ > Patent. n. Genius is 5% inspiration and 95% perspiration. A patent is a > tool for doing 5% of the work and then sitting around waiting for someone > else to do the other 95% so you can sue them.
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