Thread: Index on parent/child hierarchy

Hi

I'm looking for advice on the best way to index a table that is defined as:

create table uuid.master(id uuid, parent uuid references
uuid.master(id), type_id smallint, primary key(id));

Besides the primary key, I have these two indices on the table too:
CREATE INDEX master_parent_idx ON uuid.master(parent);
CREATE INDEX master_type_idx ON uuid.master(type_id);

I have data arranged in four levels (ie type_id is from 1 to 4):

1. id=A type_id=1
2.  id=B parent=A type_id=2
3.   id=C parent=B type_id=3
4.    id=D parent=C type_id=4
2.  id=E parent=A type_id=2
3.   id=F parent=E type_id=3
4.    id=G parent=F type_id=4
4.    id=H parent=F type_id=4
4.    id=I parent=F type_id=4
3.   id=J parent=E type_id=3
4.    id=K parent=J type_id=4

I want to count all type_id=4 for a particular type_id=1 uuid.

I use this query:

SELECT count(t4.id)
FROM uuid.master AS t4
INNER JOIN uuid.master AS t3 ON t4.parent=t3.id
INNER JOIN uuid.master AS t2 ON t3.parent=t2.id
INNER JOIN uuid.master AS t1 ON t2.parent=t1.id
WHERE t1.id=UUID

Apart from creating a separate table to keep track of the counts, is
there a good way to index the table to help?

Regards,

--
Jason Armstrong

On Wed, Jan 25, 2012 at 11:54 AM, Jason Armstrong <ja@riverdrums.com> wrote:
> Hi
>
> I'm looking for advice on the best way to index a table that is defined as:
>
> create table uuid.master(id uuid, parent uuid references
> uuid.master(id), type_id smallint, primary key(id));
>
> Besides the primary key, I have these two indices on the table too:
> CREATE INDEX master_parent_idx ON uuid.master(parent);
> CREATE INDEX master_type_idx ON uuid.master(type_id);
>
> I have data arranged in four levels (ie type_id is from 1 to 4):
>
> 1. id=A type_id=1
> 2.  id=B parent=A type_id=2
> 3.   id=C parent=B type_id=3
> 4.    id=D parent=C type_id=4
> 2.  id=E parent=A type_id=2
> 3.   id=F parent=E type_id=3
> 4.    id=G parent=F type_id=4
> 4.    id=H parent=F type_id=4
> 4.    id=I parent=F type_id=4
> 3.   id=J parent=E type_id=3
> 4.    id=K parent=J type_id=4
>
> I want to count all type_id=4 for a particular type_id=1 uuid.
>
> I use this query:
>
> SELECT count(t4.id)
> FROM uuid.master AS t4
> INNER JOIN uuid.master AS t3 ON t4.parent=t3.id
> INNER JOIN uuid.master AS t2 ON t3.parent=t2.id
> INNER JOIN uuid.master AS t1 ON t2.parent=t1.id
> WHERE t1.id=UUID
>
> Apart from creating a separate table to keep track of the counts, is
> there a good way to index the table to help?

Something like this...

WITH RECURSIVE subtree(depth, id, parent, type_id) AS (
    SELECT 0, id, parent, type_id FROM uuid.master WHERE id = X
  UNION
    SELECT depth+1, m.id, m.parent, m.type_id
    FROM subtree t, uuid.master m
    WHERE m.parent = t.id
  )
SELECT count(*)
FROM subtree
WHERE type_id = 4;

Add an index on id

--
 Simon Riggs                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services

On Wed, Jan 25, 2012 at 5:54 AM, Jason Armstrong <ja@riverdrums.com> wrote:
> Hi
>
> I'm looking for advice on the best way to index a table that is defined as:
>
> create table uuid.master(id uuid, parent uuid references
> uuid.master(id), type_id smallint, primary key(id));
>
> Besides the primary key, I have these two indices on the table too:
> CREATE INDEX master_parent_idx ON uuid.master(parent);
> CREATE INDEX master_type_idx ON uuid.master(type_id);
>
> I have data arranged in four levels (ie type_id is from 1 to 4):
>
> 1. id=A type_id=1
> 2.  id=B parent=A type_id=2
> 3.   id=C parent=B type_id=3
> 4.    id=D parent=C type_id=4
> 2.  id=E parent=A type_id=2
> 3.   id=F parent=E type_id=3
> 4.    id=G parent=F type_id=4
> 4.    id=H parent=F type_id=4
> 4.    id=I parent=F type_id=4
> 3.   id=J parent=E type_id=3
> 4.    id=K parent=J type_id=4
>
> I want to count all type_id=4 for a particular type_id=1 uuid.
>
> I use this query:
>
> SELECT count(t4.id)
> FROM uuid.master AS t4
> INNER JOIN uuid.master AS t3 ON t4.parent=t3.id
> INNER JOIN uuid.master AS t2 ON t3.parent=t2.id
> INNER JOIN uuid.master AS t1 ON t2.parent=t1.id
> WHERE t1.id=UUID
>
> Apart from creating a separate table to keep track of the counts, is
> there a good way to index the table to help?

If your data is organized as a tree, tends to run deep (causing many
recursion joins),  and you often make sweeping subset operations
starting from a parent node, and your data isn't too heavily updated,
you might want to consider materialized path organization instead of
parent/child.  Both arrays and strings work for that.

 id=I parents=A,E,F type_id=4

SELECT count(*) FROM uuid.master WHERE parents LIKE 'A,E%' and type_id = 4;

The point here is that you can exploit the tree structure with a btree
index.  Before we got recursive queries, this was often the best way
to do it, but now it's kind of a niche solution to be used when
certain things fall into place.

merlin

On Sun, Jan 29, 2012 at 5:55 AM, Dmitriy Igrishin <dmitigr@gmail.com> wrote:
>> The point here is that you can exploit the tree structure with a btree
>> index.  Before we got recursive queries, this was often the best way
>> to do it, but now it's kind of a niche solution to be used when
>> certain things fall into place.
>>
>> merlin
>
> Another approarch  is to use ltree. It's easy and robust.
> http://www.postgresql.org/docs/9.1/static/ltree.html

yeah -- good point.

merlin