Thread: Postgres array parser
Hello, I wanted to ask according such a problem which we had faced with.
We are widely using postgres arrays like key->value array by doing like
this:
{{1,5},{2,6},{3,7}}
where 1,2,3 are keys, and 5,6,7 are values. In our pgSql functions we
are using self written array_input(array::numeric[], key::numeric)
function which makes a loop on whole array and searches for key like
FOR i IN 1 .. size LOOP
if array[i][1] = key then
return array[i][2];
end if;
END LOOP;
But this was a good solution until our arrays and database had grown. So
now FOR loop takes a lot of time to find value of an array.
And my question is, how this problem of performance could be solved? We
had tried pgperl for string parsing, but it takes much more time than
our current solution. Also we are thinking about self-written C++
function, may be someone had implemented this algorithm before?
--
Best regards
Aleksej Trofimov
Hello do you know FOREACH IN ARRAY statement in 9.1 this significantly accelerate iteration over array http://www.depesz.com/index.php/2011/03/07/waiting-for-9-1-foreach-in-array/ 2011/12/13 Aleksej Trofimov <aleksej.trofimov@ruptela.lt>: > Hello, I wanted to ask according such a problem which we had faced with. > We are widely using postgres arrays like key->value array by doing like > this: > > {{1,5},{2,6},{3,7}} > > where 1,2,3 are keys, and 5,6,7 are values. In our pgSql functions we are > using self written array_input(array::numeric[], key::numeric) function > which makes a loop on whole array and searches for key like > FOR i IN 1 .. size LOOP > if array[i][1] = key then > return array[i][2]; > end if; > END LOOP; > > But this was a good solution until our arrays and database had grown. So now > FOR loop takes a lot of time to find value of an array. > > And my question is, how this problem of performance could be solved? We had > tried pgperl for string parsing, but it takes much more time than our > current solution. Also we are thinking about self-written C++ function, may > be someone had implemented this algorithm before? > you can use indexes or you can use hstore Regards Pavel Stehule > -- > Best regards > > Aleksej Trofimov > > > -- > Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-performance
We have tried foreach syntax, but we have noticed performance degradation:
Function with for: 203ms
Function with foreach: ~250ms:
there is functions code:
CREATE OR REPLACE FUNCTION input_value_fe(in_inputs numeric[],
in_input_nr numeric)
RETURNS numeric AS
$BODY$
declare i numeric[];
BEGIN
FOREACH i SLICE 1 IN ARRAY in_inputs
LOOP
if i[1] = in_input_nr then
return i[2];
end if;
END LOOP;
return null;
END;
$BODY$
LANGUAGE plpgsql VOLATILE
COST 100;
CREATE OR REPLACE FUNCTION input_value(in_inputs numeric[], in_input_nr
numeric)
RETURNS numeric AS
$BODY$
declare
size int;
BEGIN
size = array_upper(in_inputs, 1);
IF size IS NOT NULL THEN
FOR i IN 1 .. size LOOP
if in_inputs[i][1] = in_input_nr then
return in_inputs[i][2];
end if;
END LOOP;
END IF;
return null;
END;
$BODY$
LANGUAGE plpgsql VOLATILE
COST 100;
On 12/13/2011 04:02 PM, Pavel Stehule wrote:
> Hello
>
> do you know FOREACH IN ARRAY statement in 9.1
>
> this significantly accelerate iteration over array
>
> http://www.depesz.com/index.php/2011/03/07/waiting-for-9-1-foreach-in-array/
>
>
>
> 2011/12/13 Aleksej Trofimov<aleksej.trofimov@ruptela.lt>:
>> Hello, I wanted to ask according such a problem which we had faced with.
>> We are widely using postgres arrays like key->value array by doing like
>> this:
>>
>> {{1,5},{2,6},{3,7}}
>>
>> where 1,2,3 are keys, and 5,6,7 are values. In our pgSql functions we are
>> using self written array_input(array::numeric[], key::numeric) function
>> which makes a loop on whole array and searches for key like
>> FOR i IN 1 .. size LOOP
>> if array[i][1] = key then
>> return array[i][2];
>> end if;
>> END LOOP;
>>
>> But this was a good solution until our arrays and database had grown. So now
>> FOR loop takes a lot of time to find value of an array.
>>
>> And my question is, how this problem of performance could be solved? We had
>> tried pgperl for string parsing, but it takes much more time than our
>> current solution. Also we are thinking about self-written C++ function, may
>> be someone had implemented this algorithm before?
>>
> you can use indexes or you can use hstore
>
> Regards
>
> Pavel Stehule
>
>> --
>> Best regards
>>
>> Aleksej Trofimov
>>
>>
>> --
>> Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org)
>> To make changes to your subscription:
>> http://www.postgresql.org/mailpref/pgsql-performance
--
Best regards
Aleksej Trofimov
UAB "Ruptela"
Phone: +370 657 80475
E-Mail: aleksej.trofimov@ruptela.lt
Web: http://www.ruptela.lt
Ruptela - the most successful IT company in Lithuania 2011
Ruptela - sekmingiausia Lietuvos aukštųjų technologijų įmonė 2011
http://www.prezidentas.lt/lt/spaudos_centras_392/pranesimai_spaudai/inovatyvus_verslas_-_konkurencingos_lietuvos_pagrindas.html
http://www.ruptela.lt/news/37/121/Ruptela-sekmingiausia-jauna-aukstuju-technologiju-imone-Lietuvoje
Hello 2011/12/13 Aleksej Trofimov <aleksej.trofimov@ruptela.lt>: > We have tried foreach syntax, but we have noticed performance degradation: > Function with for: 203ms > Function with foreach: ~250ms: > > there is functions code: > CREATE OR REPLACE FUNCTION input_value_fe(in_inputs numeric[], in_input_nr > numeric) > RETURNS numeric AS > $BODY$ > declare i numeric[]; > BEGIN > FOREACH i SLICE 1 IN ARRAY in_inputs > LOOP > if i[1] = in_input_nr then > return i[2]; > end if; > END LOOP; > > return null; > END; > $BODY$ > LANGUAGE plpgsql VOLATILE > COST 100; > > CREATE OR REPLACE FUNCTION input_value(in_inputs numeric[], in_input_nr > numeric) > RETURNS numeric AS > $BODY$ > declare > size int; > BEGIN > size = array_upper(in_inputs, 1); > IF size IS NOT NULL THEN > > FOR i IN 1 .. size LOOP > if in_inputs[i][1] = in_input_nr then > return in_inputs[i][2]; > end if; > END LOOP; > END IF; > > return null; > END; > $BODY$ > LANGUAGE plpgsql VOLATILE > COST 100; > > > On 12/13/2011 04:02 PM, Pavel Stehule wrote: >> >> Hello >> >> do you know FOREACH IN ARRAY statement in 9.1 >> >> this significantly accelerate iteration over array >> >> >> http://www.depesz.com/index.php/2011/03/07/waiting-for-9-1-foreach-in-array/ >> >> >> >> 2011/12/13 Aleksej Trofimov<aleksej.trofimov@ruptela.lt>: >>> >>> Hello, I wanted to ask according such a problem which we had faced with. >>> We are widely using postgres arrays like key->value array by doing like >>> this: >>> >>> {{1,5},{2,6},{3,7}} >>> >>> where 1,2,3 are keys, and 5,6,7 are values. In our pgSql functions we are >>> using self written array_input(array::numeric[], key::numeric) function >>> which makes a loop on whole array and searches for key like >>> FOR i IN 1 .. size LOOP >>> if array[i][1] = key then >>> return array[i][2]; >>> end if; >>> END LOOP; >>> >>> But this was a good solution until our arrays and database had grown. So >>> now >>> FOR loop takes a lot of time to find value of an array. >>> >>> And my question is, how this problem of performance could be solved? We >>> had >>> tried pgperl for string parsing, but it takes much more time than our >>> current solution. Also we are thinking about self-written C++ function, >>> may >>> be someone had implemented this algorithm before? >>> >> you can use indexes or you can use hstore >> >> Regards >> >> Pavel Stehule >> >>> -- >>> Best regards >>> >>> Aleksej Trofimov >>> >>> >>> -- >>> Sent via pgsql-performance mailing list >>> (pgsql-performance@postgresql.org) >>> To make changes to your subscription: >>> http://www.postgresql.org/mailpref/pgsql-performance > > It is strange - on my comp FOREACH is about 2x faster postgres=# select input_value(array(select generate_series(1,1000000)::numeric), 100000); input_value ------------- (1 row) Time: 495.426 ms postgres=# select input_value_fe(array(select generate_series(1,1000000)::numeric), 100000); input_value_fe ---------------- (1 row) Time: 248.980 ms Regards Pavel > > -- > Best regards > > Aleksej Trofimov > > UAB "Ruptela" > > Phone: +370 657 80475 > > E-Mail: aleksej.trofimov@ruptela.lt > Web: http://www.ruptela.lt > > Ruptela - the most successful IT company in Lithuania 2011 > Ruptela - sekmingiausia Lietuvos aukštųjų technologijų įmonė 2011 > http://www.prezidentas.lt/lt/spaudos_centras_392/pranesimai_spaudai/inovatyvus_verslas_-_konkurencingos_lietuvos_pagrindas.html > http://www.ruptela.lt/news/37/121/Ruptela-sekmingiausia-jauna-aukstuju-technologiju-imone-Lietuvoje >
Hello, For such cases (see below), it would be nice to have an unnest function that only affect the first array dimension. Something like unnest(ARRAY[[1,2],[2,3]], SLICE=1) => unnest ------ [1,2] [2,3] With this function, I imagine that following sql function might beat the plpgsql FOREACH version. CREATE OR REPLACE FUNCTION input_value_un (in_inputs numeric[], in_input_nr numeric) RETURNS numeric AS $BODY$ SELECT u[1][2] FROM unnest($1, SLICE =1) u WHERE u[1][1]=in_input_nr LIMIT 1; $BODY$ LANGUAGE sql IMMUTABLE; best regards, Marc Mamin > -----Original Message----- > From: pgsql-performance-owner@postgresql.org [mailto:pgsql-performance- > owner@postgresql.org] On Behalf Of Pavel Stehule > Sent: Dienstag, 13. Dezember 2011 15:43 > To: Aleksej Trofimov > Cc: pgsql-performance@postgresql.org > Subject: Re: [PERFORM] Postgres array parser > > Hello > > 2011/12/13 Aleksej Trofimov <aleksej.trofimov@ruptela.lt>: > > We have tried foreach syntax, but we have noticed performance > degradation: > > Function with for: 203ms > > Function with foreach: ~250ms: > > > > there is functions code: > > CREATE OR REPLACE FUNCTION input_value_fe(in_inputs numeric[], > in_input_nr > > numeric) > > RETURNS numeric AS > > $BODY$ > > declare i numeric[]; > > BEGIN > > FOREACH i SLICE 1 IN ARRAY in_inputs > > LOOP > > if i[1] = in_input_nr then > > return i[2]; > > end if; > > END LOOP; > > > > return null; > > END; > > $BODY$ > > LANGUAGE plpgsql VOLATILE > > COST 100; > > > > CREATE OR REPLACE FUNCTION input_value(in_inputs numeric[], > in_input_nr > > numeric) > > RETURNS numeric AS > > $BODY$ > > declare > > size int; > > BEGIN > > size = array_upper(in_inputs, 1); > > IF size IS NOT NULL THEN > > > > FOR i IN 1 .. size LOOP > > if in_inputs[i][1] = in_input_nr then > > return in_inputs[i][2]; > > end if; > > END LOOP; > > END IF; > > > > return null; > > END; > > $BODY$ > > LANGUAGE plpgsql VOLATILE > > COST 100; > > > > > > On 12/13/2011 04:02 PM, Pavel Stehule wrote: > >> > >> Hello > >> > >> do you know FOREACH IN ARRAY statement in 9.1 > >> > >> this significantly accelerate iteration over array > >> > >> > >> http://www.depesz.com/index.php/2011/03/07/waiting-for-9-1-foreach- > in-array/ > >> > >> > >> > >> 2011/12/13 Aleksej Trofimov<aleksej.trofimov@ruptela.lt>: > >>> > >>> Hello, I wanted to ask according such a problem which we had faced > with. > >>> We are widely using postgres arrays like key->value array by doing > like > >>> this: > >>> > >>> {{1,5},{2,6},{3,7}} > >>> > >>> where 1,2,3 are keys, and 5,6,7 are values. In our pgSql functions > we are > >>> using self written array_input(array::numeric[], key::numeric) > function > >>> which makes a loop on whole array and searches for key like > >>> FOR i IN 1 .. size LOOP > >>> if array[i][1] = key then > >>> return array[i][2]; > >>> end if; > >>> END LOOP; > >>> > >>> But this was a good solution until our arrays and database had > grown. So > >>> now > >>> FOR loop takes a lot of time to find value of an array. > >>> > >>> And my question is, how this problem of performance could be > solved? We > >>> had > >>> tried pgperl for string parsing, but it takes much more time than > our > >>> current solution. Also we are thinking about self-written C++ > function, > >>> may > >>> be someone had implemented this algorithm before? > >>> > >> you can use indexes or you can use hstore > >> > >> Regards > >> > >> Pavel Stehule > >> > >>> -- > >>> Best regards > >>> > >>> Aleksej Trofimov > >>> > >>> > >>> -- > >>> Sent via pgsql-performance mailing list > >>> (pgsql-performance@postgresql.org) > >>> To make changes to your subscription: > >>> http://www.postgresql.org/mailpref/pgsql-performance > > > > > > It is strange - on my comp FOREACH is about 2x faster > > postgres=# select input_value(array(select > generate_series(1,1000000)::numeric), 100000); > input_value > ------------- > > (1 row) > > Time: 495.426 ms > > postgres=# select input_value_fe(array(select > generate_series(1,1000000)::numeric), 100000); > input_value_fe > ---------------- > > (1 row) > > Time: 248.980 ms > > Regards > > Pavel > > > > > > -- > > Best regards > > > > Aleksej Trofimov > > > > UAB "Ruptela" > > > > Phone: +370 657 80475 > > > > E-Mail: aleksej.trofimov@ruptela.lt > > Web: http://www.ruptela.lt > > > > Ruptela - the most successful IT company in Lithuania 2011 > > Ruptela - sekmingiausia Lietuvos aukštųjų technologijų įmonė 2011 > > > http://www.prezidentas.lt/lt/spaudos_centras_392/pranesimai_spaudai/ino > vatyvus_verslas_-_konkurencingos_lietuvos_pagrindas.html > > http://www.ruptela.lt/news/37/121/Ruptela-sekmingiausia-jauna- > aukstuju-technologiju-imone-Lietuvoje > > > > -- > Sent via pgsql-performance mailing list (pgsql- > performance@postgresql.org) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-performance
Yes, it would be great, but I haven't found such a function, which splits 2 dimensional array into rows =) Maybe we'll modify existing function, but unfortunately we have tried hstore type and function in postgres and we see a significant performance improvements. So we only need to convert existing data into hstore and I think this is a good solution. On 12/14/2011 11:21 AM, Marc Mamin wrote: > Hello, > > For such cases (see below), it would be nice to have an unnest function that only affect the first array dimension. > > Something like > > unnest(ARRAY[[1,2],[2,3]], SLICE=1) > => > unnest > ------ > [1,2] > [2,3] > > > With this function, I imagine that following sql function > might beat the plpgsql FOREACH version. > > > CREATE OR REPLACE FUNCTION input_value_un (in_inputs numeric[], in_input_nr numeric) > RETURNS numeric AS > $BODY$ > > SELECT u[1][2] > FROM unnest($1, SLICE =1) u > WHERE u[1][1]=in_input_nr > LIMIT 1; > > $BODY$ > LANGUAGE sql IMMUTABLE; > > > > best regards, > > Marc Mamin > > >> -----Original Message----- >> From: pgsql-performance-owner@postgresql.org [mailto:pgsql-performance- >> owner@postgresql.org] On Behalf Of Pavel Stehule >> Sent: Dienstag, 13. Dezember 2011 15:43 >> To: Aleksej Trofimov >> Cc: pgsql-performance@postgresql.org >> Subject: Re: [PERFORM] Postgres array parser >> >> Hello >> >> 2011/12/13 Aleksej Trofimov<aleksej.trofimov@ruptela.lt>: >>> We have tried foreach syntax, but we have noticed performance >> degradation: >>> Function with for: 203ms >>> Function with foreach: ~250ms: >>> >>> there is functions code: >>> CREATE OR REPLACE FUNCTION input_value_fe(in_inputs numeric[], >> in_input_nr >>> numeric) >>> RETURNS numeric AS >>> $BODY$ >>> declare i numeric[]; >>> BEGIN >>> FOREACH i SLICE 1 IN ARRAY in_inputs >>> LOOP >>> if i[1] = in_input_nr then >>> return i[2]; >>> end if; >>> END LOOP; >>> >>> return null; >>> END; >>> $BODY$ >>> LANGUAGE plpgsql VOLATILE >>> COST 100; >>> >>> CREATE OR REPLACE FUNCTION input_value(in_inputs numeric[], >> in_input_nr >>> numeric) >>> RETURNS numeric AS >>> $BODY$ >>> declare >>> size int; >>> BEGIN >>> size = array_upper(in_inputs, 1); >>> IF size IS NOT NULL THEN >>> >>> FOR i IN 1 .. size LOOP >>> if in_inputs[i][1] = in_input_nr then >>> return in_inputs[i][2]; >>> end if; >>> END LOOP; >>> END IF; >>> >>> return null; >>> END; >>> $BODY$ >>> LANGUAGE plpgsql VOLATILE >>> COST 100; >>> >>> >>> On 12/13/2011 04:02 PM, Pavel Stehule wrote: >>>> Hello >>>> >>>> do you know FOREACH IN ARRAY statement in 9.1 >>>> >>>> this significantly accelerate iteration over array >>>> >>>> >>>> http://www.depesz.com/index.php/2011/03/07/waiting-for-9-1-foreach- >> in-array/ >>>> >>>> >>>> 2011/12/13 Aleksej Trofimov<aleksej.trofimov@ruptela.lt>: >>>>> Hello, I wanted to ask according such a problem which we had faced >> with. >>>>> We are widely using postgres arrays like key->value array by doing >> like >>>>> this: >>>>> >>>>> {{1,5},{2,6},{3,7}} >>>>> >>>>> where 1,2,3 are keys, and 5,6,7 are values. In our pgSql functions >> we are >>>>> using self written array_input(array::numeric[], key::numeric) >> function >>>>> which makes a loop on whole array and searches for key like >>>>> FOR i IN 1 .. size LOOP >>>>> if array[i][1] = key then >>>>> return array[i][2]; >>>>> end if; >>>>> END LOOP; >>>>> >>>>> But this was a good solution until our arrays and database had >> grown. So >>>>> now >>>>> FOR loop takes a lot of time to find value of an array. >>>>> >>>>> And my question is, how this problem of performance could be >> solved? We >>>>> had >>>>> tried pgperl for string parsing, but it takes much more time than >> our >>>>> current solution. Also we are thinking about self-written C++ >> function, >>>>> may >>>>> be someone had implemented this algorithm before? >>>>> >>>> you can use indexes or you can use hstore >>>> >>>> Regards >>>> >>>> Pavel Stehule >>>> >>>>> -- >>>>> Best regards >>>>> >>>>> Aleksej Trofimov >>>>> >>>>> >>>>> -- >>>>> Sent via pgsql-performance mailing list >>>>> (pgsql-performance@postgresql.org) >>>>> To make changes to your subscription: >>>>> http://www.postgresql.org/mailpref/pgsql-performance >>> >> It is strange - on my comp FOREACH is about 2x faster >> >> postgres=# select input_value(array(select >> generate_series(1,1000000)::numeric), 100000); >> input_value >> ------------- >> >> (1 row) >> >> Time: 495.426 ms >> >> postgres=# select input_value_fe(array(select >> generate_series(1,1000000)::numeric), 100000); >> input_value_fe >> ---------------- >> >> (1 row) >> >> Time: 248.980 ms >> >> Regards >> >> Pavel >> >> >> -- >> Sent via pgsql-performance mailing list (pgsql- >> performance@postgresql.org) >> To make changes to your subscription: >> http://www.postgresql.org/mailpref/pgsql-performance -- Best regards Aleksej Trofimov
> Yes, it would be great, but I haven't found such a function, which
> splits 2 dimensional array into rows =) Maybe we'll modify existing
> function, but unfortunately we have tried hstore type and function in
> postgres and we see a significant performance improvements. So we only
> need to convert existing data into hstore and I think this is a good
> solution.
I haven't tested hstore yet, but I would be interested to find out if it still better perform with custom "numeric"
aggregateson the hstore values.
I've made a short "proof of concept" test with a custom key/value type to achieve such an aggregation.
Something like:
SELECT x, distinct_sum( (currency,amount)::keyval ) overview FROM ... GROUP BY x
x currency amount
a EUR 15.0
a EUR 5.0
a CHF 7.5
b USD 12.0
=>
x overview
- --------
a {(EUR,20.0), (CHF,7.5)}
b {(USD,10.0)}
regards,
Marc Mamin
> On 12/14/2011 11:21 AM, Marc Mamin wrote:
> > Hello,
> >
> > For such cases (see below), it would be nice to have an unnest
> function that only affect the first array dimension.
> >
> > Something like
> >
> > unnest(ARRAY[[1,2],[2,3]], SLICE=1)
> > =>
> > unnest
> > ------
> > [1,2]
> > [2,3]
> >
> >
> > With this function, I imagine that following sql function
> > might beat the plpgsql FOREACH version.
> >
> >
> > CREATE OR REPLACE FUNCTION input_value_un (in_inputs numeric[],
> in_input_nr numeric)
> > RETURNS numeric AS
> > $BODY$
> >
> > SELECT u[1][2]
> > FROM unnest($1, SLICE =1) u
> > WHERE u[1][1]=in_input_nr
> > LIMIT 1;
> >
> > $BODY$
> > LANGUAGE sql IMMUTABLE;
> >
> >
> >
> > best regards,
> >
> > Marc Mamin
> >
> >
> >> -----Original Message-----
> >> From: pgsql-performance-owner@postgresql.org [mailto:pgsql-
> performance-
> >> owner@postgresql.org] On Behalf Of Pavel Stehule
> >> Sent: Dienstag, 13. Dezember 2011 15:43
> >> To: Aleksej Trofimov
> >> Cc: pgsql-performance@postgresql.org
> >> Subject: Re: [PERFORM] Postgres array parser
> >>
> >> Hello
> >>
> >> 2011/12/13 Aleksej Trofimov<aleksej.trofimov@ruptela.lt>:
> >>> We have tried foreach syntax, but we have noticed performance
> >> degradation:
> >>> Function with for: 203ms
> >>> Function with foreach: ~250ms:
> >>>
> >>> there is functions code:
> >>> CREATE OR REPLACE FUNCTION input_value_fe(in_inputs numeric[],
> >> in_input_nr
> >>> numeric)
> >>> RETURNS numeric AS
> >>> $BODY$
> >>> declare i numeric[];
> >>> BEGIN
> >>> FOREACH i SLICE 1 IN ARRAY in_inputs
> >>> LOOP
> >>> if i[1] = in_input_nr then
> >>> return i[2];
> >>> end if;
> >>> END LOOP;
> >>>
> >>> return null;
> >>> END;
> >>> $BODY$
> >>> LANGUAGE plpgsql VOLATILE
> >>> COST 100;
> >>>
> >>> CREATE OR REPLACE FUNCTION input_value(in_inputs numeric[],
> >> in_input_nr
> >>> numeric)
> >>> RETURNS numeric AS
> >>> $BODY$
> >>> declare
> >>> size int;
> >>> BEGIN
> >>> size = array_upper(in_inputs, 1);
> >>> IF size IS NOT NULL THEN
> >>>
> >>> FOR i IN 1 .. size LOOP
> >>> if in_inputs[i][1] = in_input_nr then
> >>> return in_inputs[i][2];
> >>> end if;
> >>> END LOOP;
> >>> END IF;
> >>>
> >>> return null;
> >>> END;
> >>> $BODY$
> >>> LANGUAGE plpgsql VOLATILE
> >>> COST 100;
> >>>
> >>>
> >>> On 12/13/2011 04:02 PM, Pavel Stehule wrote:
> >>>> Hello
> >>>>
> >>>> do you know FOREACH IN ARRAY statement in 9.1
> >>>>
> >>>> this significantly accelerate iteration over array
> >>>>
> >>>>
> >>>> http://www.depesz.com/index.php/2011/03/07/waiting-for-9-1-
> foreach-
> >> in-array/
> >>>>
> >>>>
> >>>> 2011/12/13 Aleksej Trofimov<aleksej.trofimov@ruptela.lt>:
> >>>>> Hello, I wanted to ask according such a problem which we had
> faced
> >> with.
> >>>>> We are widely using postgres arrays like key->value array by
> doing
> >> like
> >>>>> this:
> >>>>>
> >>>>> {{1,5},{2,6},{3,7}}
> >>>>>
> >>>>> where 1,2,3 are keys, and 5,6,7 are values. In our pgSql
> functions
> >> we are
> >>>>> using self written array_input(array::numeric[], key::numeric)
> >> function
> >>>>> which makes a loop on whole array and searches for key like
> >>>>> FOR i IN 1 .. size LOOP
> >>>>> if array[i][1] = key then
> >>>>> return array[i][2];
> >>>>> end if;
> >>>>> END LOOP;
> >>>>>
> >>>>> But this was a good solution until our arrays and database had
> >> grown. So
> >>>>> now
> >>>>> FOR loop takes a lot of time to find value of an array.
> >>>>>
> >>>>> And my question is, how this problem of performance could be
> >> solved? We
> >>>>> had
> >>>>> tried pgperl for string parsing, but it takes much more time than
> >> our
> >>>>> current solution. Also we are thinking about self-written C++
> >> function,
> >>>>> may
> >>>>> be someone had implemented this algorithm before?
> >>>>>
> >>>> you can use indexes or you can use hstore
> >>>>
> >>>> Regards
> >>>>
> >>>> Pavel Stehule
> >>>>
> >>>>> --
> >>>>> Best regards
> >>>>>
> >>>>> Aleksej Trofimov
> >>>>>
> >>>>>
> >>>>> --
> >>>>> Sent via pgsql-performance mailing list
> >>>>> (pgsql-performance@postgresql.org)
> >>>>> To make changes to your subscription:
> >>>>> http://www.postgresql.org/mailpref/pgsql-performance
> >>>
> >> It is strange - on my comp FOREACH is about 2x faster
> >>
> >> postgres=# select input_value(array(select
> >> generate_series(1,1000000)::numeric), 100000);
> >> input_value
> >> -------------
> >>
> >> (1 row)
> >>
> >> Time: 495.426 ms
> >>
> >> postgres=# select input_value_fe(array(select
> >> generate_series(1,1000000)::numeric), 100000);
> >> input_value_fe
> >> ----------------
> >>
> >> (1 row)
> >>
> >> Time: 248.980 ms
> >>
> >> Regards
> >>
> >> Pavel
> >>
> >>
> >> --
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>
>
> --
> Best regards
>
> Aleksej Trofimov
>
>
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