[PostgreSQL-Hackers] patch submission: truncate trailing nulls from heap rows to reduce the size of the null bitmap

[PostgreSQL-Hackers] patch submission: truncate trailing nulls from heap rows to reduce the size of the null bitmap

	Josh Berkus
	May 3, 2012 at 6:52 pm

Tom,

So that I can test this properly, what is the specific use-case we'd
expect to be slow with this patch?

--
Josh Berkus
PostgreSQL Experts Inc.
http://pgexperts.com

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Josh Berkus: Nice, thanks. I'll try some of my own tests when I get a chance; I have a really good use-case for this optimization. -- Josh Berkus PostgreSQL Experts Inc. http://pgexperts.com

Follow ups

Robert Haas: Josh, The CommitFest application lists you as the reviewer for this patch. Are you (I hope) planning to review it? I see you posted up a follow-up email asking Tom what he had in mind. Personally, I don't think this needs incredibly complicated testing. I think you should just test a workload involving inserting and/or updating rows with lots of trailing NULL columns, and then another workload with a table of similar width that... doesn't. If we can't find a regression - or, better, we find a
Simon Riggs: This is an interesting patch, but its has had various comments made about it. When I look at this I see that it would change the NULL bitmap for all existing rows, which means it forces a complete unload/reload of data. We've moved away from doing things like that, so in its current form we'd probably want to reject that. If I might suggest a way forward? Keep NULL bitmaps as they are now. Have another flag which indicates when a partial trailing col trimmed NULL bitmap is in use. Then we can
Tom Lane: Huh? I thought it would only change how *new* tuples were stored. Old tuples ought to continue to work fine. I'm not really convinced that it's a good idea in the larger scheme of things --- your point in a nearby thread that micro-optimizing storage space at the expense of all else is not good engineering applies here. But I don't see that it forces data reload. Or if it does, that should be easily fixable. That might be useful for forensic purposes, but on the whole I suspect it's just added

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[PostgreSQL-Hackers] patch submission: truncate trailing nulls from heap rows to reduce the size of the null bitmap

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