Tom Lane wrote:
I recognize the added cost of implementing index only scans. As storage is relatively cheap these days, everyone I know is more concerned about faster access to data. Similarly, it would still be faster to scan the indexes than to perform a sequential scan over the entire relation for this case. I also acknowledge that it would be a negative impact to indexes where this type of acces isn't required, as you suggested and which is more than likely not the case. I just wonder what more people would be happier with and whether the added 16-20 bytes would be extremely noticable considering most 1-3 year old hardware.The fundamental problem is that you can't do it without adding at least 16 bytes, probably 20, to the size of an index tuple header. That would double the physical size of an index on a simple column (eg an integer or timestamp). The extra I/O costs and extra maintenance costs are unattractive to say the least. And it takes away some of the justification for the whole thing, which is that reading an index is much cheaper than reading the main table. That's only true if the index is much smaller than the main table ...
regards, tom lane
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