Horton

Re: [HACKERS] Aggregate transition state merging vs. hypothetical set functions

Peter Eisentraut <peter.eisentraut@2ndquadrant.com>

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From: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>
To: Tom Lane <tgl@sss.pgh.pa.us>, Heikki Linnakangas <hlinnaka@iki.fi>
Cc: David Rowley <david.rowley@2ndquadrant.com>, pgsql-hackers@postgresql.org
Date: 2018-05-21T14:14:58Z
Lists: pgsql-hackers 
On 10/13/17 19:01, Tom Lane wrote:
>> Moving on to the exact color of the bikeshed: it seems like the right
>> way to present this to users of CREATE AGGREGATE is in terms of "does
>> the final function modify the transition state?".  So maybe the values
>> could be spelled
>> SMODIFY = READ_ONLY   ffunc never touches state, ok as window agg
>> SMODIFY = SHARABLE    ffunc does some one-time change like sorting,
>>                       so state merging is OK but not window agg
>> SMODIFY = READ_WRITE  ffunc trashes state, can't do merging either
>> I'm not set on these names by any means; anyone have a better idea?

Is "sharable" the preferred spelling, as opposed to "shareable"?

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

Commits

  1. Improve spelling of new FINALFUNC_MODIFY aggregate attribute.

  2. Explicitly track whether aggregate final functions modify transition state.