public inbox for [email protected]  

help / color / mirror / Atom feed

From: Vallimaharajan G <[email protected]>
To: pgsql-hackers <[email protected]>
Subject: Query Regarding frame options initialization in Window aggregate state
Date: Wed, 27 Mar 2024 14:37:43 +0530
Message-ID: <[email protected]> (raw)

Hi Team,

     I am currently referring to the Postgres source code (psql (PostgreSQL) 14.3) and came across a particular section related to window aggregate initialization that has left me with a question. Specifically, I noticed a conditional case in the initialization of per aggregate (initialize_peraggregate in nodeWindowAgg.c) where the winstate frameOptions is being checked, but it appears that frameOptions is not set before this conditional case. I observed the same behaviour in PG version 16 as well.





/*

* Figure out whether we want to use the moving-aggregate implementation,

* and collect the right set of fields from the pg_attribute entry.

*

* It's possible that an aggregate would supply a safe moving-aggregate

* implementation and an unsafe normal one, in which case our hand is

* forced.  Otherwise, if the frame head can't move, we don't need

* moving-aggregate code.  Even if we'd like to use it, don't do so if the

* aggregate's arguments (and FILTER clause if any) contain any calls to

* volatile functions.  Otherwise, the difference between restarting and

* not restarting the aggregation would be user-visible.

*/

if (!OidIsValid(aggform->aggminvtransfn))

use_ma_code = false; /* sine qua non */

else if (aggform->aggmfinalmodify == AGGMODIFY_READ_ONLY &&

aggform->aggfinalmodify != AGGMODIFY_READ_ONLY)

use_ma_code = true; /* decision forced by safety */

else if (winstate->frameOptions & FRAMEOPTION_START_UNBOUNDED_PRECEDING)

use_ma_code = false; /* non-moving frame head */

else if (contain_volatile_functions((Node *) wfunc))

use_ma_code = false; /* avoid possible behavioral change */

else

use_ma_code = true; /* yes, let's use it */

if (use_ma_code)

{

peraggstate->transfn_oid = transfn_oid = aggform->aggmtransfn;

peraggstate->invtransfn_oid = invtransfn_oid = aggform->aggminvtransfn;

peraggstate->finalfn_oid = finalfn_oid = aggform->aggmfinalfn;

finalextra = aggform->aggmfinalextra;

finalmodify = aggform->aggmfinalmodify;

aggtranstype = aggform->aggmtranstype;

initvalAttNo = Anum_pg_aggregate_aggminitval;

}


   

Frame options are being set to winstate after the initialization of peraggregate. (line 2504 in nodeWindowAgg.c)



/* copy frame options to state node for easy access */

winstate->frameOptions = frameOptions;




Could you kindly share the reason why this conditional case was added during the initialization of per aggregate, especially considering that winstate frameOptions is set after this initialization?



Thanks
Vallimaharajan G

view thread (3+ messages)  latest in thread

reply

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Reply to all the recipients using the --to and --cc options:
  reply via email

  To: [email protected]
  Cc: [email protected]
  Subject: Re: Query Regarding frame options initialization in Window aggregate state
  In-Reply-To: <[email protected]>

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

This inbox is served by agora; see mirroring instructions
for how to clone and mirror all data and code used for this inbox