"Kevin Grittner" <[email protected]> writes:
> Robert Haas <[email protected]> wrote:
>> The trouble is, AFAICS, that you can't bound M very well without
>> scanning the whole table. I mean, it's bounded by theoretical
>> limit, but that's it.
> What would the theoretical limit be? (black size - page header size
> - minimum size of one tuple) / item pointer size? So, on an 8KB
> page, somewhere in the neighborhood of 1350?
Your math is off --- I get something less than 300, even if the tuples
are assumed to be empty of data. (Header size 24 bytes, plus 4-byte
line pointer, so at least 28 bytes per tuple, so at most 292 on an 8K
page.) But you still end up probing just about every page for a 1%
sample.
regards, tom lane
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