Hi,

On 6/21/17 9:47 PM, Robert Haas wrote:
...
>
like int8 or numeric, it won't work at all.  Even for other things,
it's going to cause problems because the bit patterns won't be what
the code is expecting; e.g. bitmap scans care about the structure of
the TID, not just how many bits it is.  (Due credit: Somebody, maybe
Alvaro, pointed out this problem before, at PGCon.)


Can you elaborate a bit more about this TID bit pattern issues? I do remember that not all TIDs are valid due to safeguards on individual fields, like for example

    Assert(iptr->ip_posid < (1 << MaxHeapTuplesPerPageBits))

But perhaps there are some other issues?

regards

--
Tomas Vondra                  http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services


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