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From "Olivier Chedru" <oChe...@infovista.com>
Subject Horizontal partitioning?
Date Mon, 16 Jul 2007 07:39:01 GMT
Hi all,


I am trying to achieve horizontal partitioning with Derby.


My application stores *a lot* of data as time passes, and it needs to
drop obsolete data.


Table partitioning would be the ideal solution, but it is not
implemented in Derby. So I create one table per period of time. All
tables have the same columns, the first one being the data timestamp.
Dropping obsolete data is then made easy: just drop old tables.


Now, I need to query data without knowing how tables are organized. So,
I create a view on all tables (the view is deleted/created every time a
data table is created/dropped): fine.

However, checking the runtime statistics, I notice ALL tables are
scanned when I use the view! Note I added constraints on the Timestamp


Sample SQL:


create table t1 (ts timestamp, a int, b int, c int);

create table t2 (ts timestamp, a int, b int, c int);

create table t3 (ts timestamp, a int, b int, c int);

alter table t1 add constraint t1_c check (ts >= '2007-07-16 09:00:00.0'
and ts < '2007-07-16 09:01:00.0');

alter table t2 add constraint t2_c check (ts >= '2007-07-16 09:01:00.0'
and ts < '2007-07-16 09:02:00.0');

alter table t3 add constraint t3_c check (ts >= '2007-07-16 09:02:00.0'
and ts < '2007-07-16 09:03:00.0');

create view t_view as select * from t1 union select * from t2 union
select * from t3;



select * from t_view where ts >= '2007-07-16 09:01:30.0' and ts <
'2007-07-16 09:02:00.0';



The displayed execution plan shows t1, t2 and t3 are scanned. I expect
only t2 is used. I also tried to force using constraints by defining the
view this way, but it did not improve the behavior:


create view t_view as select * from t1 --DERBY-PROPERTIES
constraint=t1_c union select * from t2 --DERBY-PROPERTIES
constraint=t2_c union select * from t3 --DERBY-PROPERTIES


Any idea on how to achieve horizontal partitioning?




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