Takahiro Itagaki <itagaki.takahiro@oss.ntt.co.jp> writes:
> Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> Takahiro Itagaki <itagaki.takahiro@oss.ntt.co.jp> writes:
>>> Instead, how about excluding columns in primary keys from table data?
>>
>> How will you implement "select * from mytable" ? Or even
>> "select * from mytable where non_primary_key = something" ?
> Also, we're using the same technique for TOASTed values. The cost can be
> compared with "select * from mytable where toasted_value = something", no?
No, because toast pointers point in the direction you need to traverse.
AFAICS, this proposal involves scanning the whole index to find the
matching entry, because the available pointers link from the wrong end,
that is from the index to the table.
There are also some fairly fatal problems associated with commands like
ALTER TABLE DROP PRIMARY KEY, but I see no need to worry about that
because you haven't even made a case that there's a net performance
gain possible here.
regards, tom lane