På fredag 02. mai 2014 kl. 01:58:04, skrev David G Johnston <
david.g.johns...@gmail.com <mailto:david.g.johns...@gmail.com>>: 
 Per-User caching does seem to be something that is going to be needed...

 Depending on how many users are being tracked would storing the "reader_id"
 in an indexed array improve matters?  " SELECT ... FROM message WHERE NOT (1
 = ANY(reader_ids)) ; UPDATE message SET reader_ids = reader_ids || 1 WHERE
 messageid = ..."  I'm not that familiar with how well indexes over arrays
 work or which kind is needed (i.e. gin/gist).     "is_read" is one of many 
properties being tracked for a message...     ​But you don't have to have all 
of them on the same table.  Once you've identified the messages in question 
performing a standard join onto a supplemental detail table should be fairly 
straight-forward.   Do these other properties have values when "is_read" is 
false or only when "is_read" is true?  Since you already allow for the 
possibility of a missing record (giving it the meaning of "not read")​ these 
other properties cannot currently exist in that situation.     A message might 
hold a property (ie. is_important) when is_read is FALSE (it might be set back 
to is_read=FALSE after being read the first time).   -- Andreas Jospeh Krogh 
CTO / Partner - Visena AS Mobile: +47 909 56 963 andr...@visena.com 
<mailto:andr...@visena.com> www.visena.com <https://www.visena.com>  
<https://www.visena.com>  

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