Re: AW: [HACKERS] inserts/updates problem under stressing !

Andreas,

I rewrote my function but got a problem how to know if update fails:

CREATE FUNCTION "acc_hits" (int4) RETURNS datetime AS '
Declare
keyval Alias For $1;
cnt int4;
curtime datetime;
Begin
curtime := ''now'';
Update hits set count = count + 1,last_access = curtime where msg_id = keyval;
if Not Found then
??????????
-- first_access inserted on default, last_access is NULL
Insert Into hits (msg_id,count) values (keyval, 1);
End If;
return curtime;
End;
' LANGUAGE 'plpgsql';

regards,

Oleg

On Mon, 26 Jul 1999, Zeugswetter Andreas IZ5 wrote:

> Date: Mon, 26 Jul 1999 10:31:33 +0200
> From: Zeugswetter Andreas IZ5 <Andreas(dot)Zeugswetter(at)telecom(dot)at>
> To: 'Oleg Bartunov' <oleg(at)sai(dot)msu(dot)su>
> Subject: AW: [HACKERS] inserts/updates problem under stressing !
>
>
> > CREATE FUNCTION "acc_hits" (int4) RETURNS int4 AS '
> > Declare
> > keyval Alias For $1;
> > cnt int4;
> > curtime datetime;
> > Begin
> > curtime := ''now'';
> > Select count into cnt from hits where msg_id = keyval;
> > if Not Found then
> > cnt := 1;
> > -- first_access inserted on default, last_access is NULL
> > Insert Into hits (msg_id,count) values (keyval, cnt);
> > else
> > cnt := cnt + 1;
> > Update hits set count = cnt,last_access = curtime where msg_id =
> > keyval;
> > End If;
> > return cnt;
> > End;
> > ' LANGUAGE 'plpgsql';
> >
> >
> Ok, this proc is not concurrent capable. This is because in the time between
> the select and the update some other connection can update count.
>
> 1. Change the update to:
> > Update hits set count = count+1, last_access = curtime where msg_id =
> > keyval;
> >
> 2. the insert is also not concurrent capable, since there could be two
> simultaneous
> first accesses.
>
> It looks like there will be more updates than inserts, so I would change the
> above to
> 1. try update
> 2. if num rows affected = 0 do the insert
>
> I don't know how to get the rows affected, but this should be possible.
>
> Andreas
>
>

_____________________________________________________________
Oleg Bartunov, sci.researcher, hostmaster of AstroNet,
Sternberg Astronomical Institute, Moscow University (Russia)
Internet: oleg(at)sai(dot)msu(dot)su, http://www.sai.msu.su/~megera/
phone: +007(095)939-16-83, +007(095)939-23-83