I sent two emails last night, one to -patches and one to -hackers. Neither
seems to have come through. Has anyone else seen them? I sent this email once
already too and it hasn't come through. I'm resending it from a different
On -patches I posted an updated patch that was functionally a noop but changed
the macro api to SETVARSIZE(). It also replaced the VARATT_SIZE and
VARATT_DATA macros with VARSIZE and VARDATA, changed inet to call detoast, and
changed arrays, inet, geometric data types and a handful of others to use
SET_VARSIZE instead of accessing a struct member directly.
On -hackers I reposted Tom's email where he proposed two sets of bitpatterns
with tradeoffs and also included an additional one that was the second of his
with the 2-byte cases removed.
In it I said that removing the 2-byte cases had no advantages but actually
since then I've thought of one. It makes the toaster code simpler since it can
just set a bit in the four-byte header just as it does now. It doesn't have to
worry about converting to a 2-byte header.
So I'm thinking of doing it for now at least. I still think paying 2 bytes on
virtually every datum is silly even if mathematically it's only 2% space
savings that's still a 2% performance penalty on sequential scans and it gains
us nothing except a few lines of code saved in tuptoaster.c.
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TIP 9: In versions below 8.0, the planner will ignore your desire to
choose an index scan if your joining column's datatypes do not