From: | "Pavel Stehule" <pavel(dot)stehule(at)gmail(dot)com> |
---|---|
To: | Anton <anton200(at)gmail(dot)com> |
Cc: | pgsql-general(at)postgresql(dot)org |
Subject: | Re: how to use array with "holes" ? |
Date: | 2007-06-01 11:37:42 |
Message-ID: | 162867790706010437m51e9cb35m53b165dc66cc88fd@mail.gmail.com |
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Thread: | |
Lists: | pgsql-general |
> initialisation:
> FOR p_tmp IN SELECT DISTINCT ON(ttc_id) ttc_id FROM ttc_ids
> LOOP
> -- get next value for index
> i = array_upper(p_ttc_ids, 1) + 1; IF i IS NULL THEN i := 0; END IF;
> --RAISE NOTICE '[%]', i;
> p_ttc_ids[i] := p_tmp.ttc_id;
> p_bytes_in[i] := 0;
> p_bytes_out[i] := 0;
> END LOOP;
>
This isn't well style for plpgsql. It's slow for bigger arrays.
create or replace function filltest1(int) returns void as $$
declare a int[];
begin
for i in 1..$1 loop
a[i] := 0;
end loop;
end; $$ language plpgsql;
-- with trick, its necessary for $1> 8000
create or replace function filltest2(int) returns void as $$
declare a int[];
begin
a := case $1 when 0 then '{}' when 1 then '{0}' else
'{0'||repeat(',0', $1-1) || '}' end;
end; $$ language plpgsql;
filltest2 is more cryptographic , but is 10-20% faster and for
sizeof(a) > ~ 8000 is 30x faster. If you now max size of array you can
do:
declare a int[] = '{0,0,0,0..........}'; b int[] = '{....}'
every array update generates new version of array -> update is more
expensive than you can know from classic languages.
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