Subject: Re: Pluggable storage
To: Robert Haas <robertmhaas@gmail.com>,
 Haribabu Kommi <kommi.haribabu@gmail.com>
Cc: Alvaro Herrera <alvherre@2ndquadrant.com>,
 Pg Hackers <pgsql-hackers@postgresql.org>
References: <20160824182201.GA232997@alvherre.pgsql>
 <20161013202642.ksiuyx72gu6wgupf@alvherre.pgsql>
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From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Message-ID: <5863132d-a436-321b-6ef9-7c5173bd8ef3@2ndquadrant.com>
Date: Thu, 22 Jun 2017 23:27:11 +0200
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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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