On 2/23/15 5:09 PM, Tomas Vondra wrote:
Over the time I've heard various use cases for this patch, but in most cases it was quite speculative. If you have an idea where this might be useful, can you explain it here, or maybe point me to a place where it's described?
For better or worse, table structure is a form of documentation for a system. As such, it's very valuable to group related fields in a table together. When creating a table, that's easy, but as soon as you need to alter your careful ordering can easily end up out the window.
Perhaps to some that just sounds like pointless window dressing, but my experience is that on a complex system the less organized things are the more bugs you get due to overlooking something.
The other reason for this patch (which it maybe doesn't support anymore?) is to allow Postgres to use an optimal physical ordering of fields on a page to reduce space wasted on alignment, as well as taking nullability and varlena into account.
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