私はリレーショナルデータベース(Firebird)に2つのテーブルedge
とnode
(隣接リストモデル)を持つDAGを持っています。私はそれらを再帰的にクエリしたいが、再帰的なクエリは非常に非効率的であることがわかった。そこで私は、Dong et.alに続いて推移的閉鎖を維持するためのトリガーを実装しようとしました。ペーパーhttp://homepages.inf.ed.ac.uk/libkin/papers/tc-sql.pdf。推移閉包表を効率的に維持する方法は?
SELECT
は非常に高速ですが、ほとんどのグラフが1回の削除でコピーされるため、DELETE
は非常に遅いです。さらに悪いことに、同時更新は不可能に思えます。
これを実装するより良い方法はありますか?
編集
私はいくつかの実験を行なったし、TCテーブルに参照カウンタを導入しました。これで、削除は高速です。私はいくつかの簡単なテストケースを書いたが、私が正しいことをしているかどうかは分からない。これは私がこれまで持っているものです:
CREATE GENERATOR graph_tc_seq;
CREATE TABLE EDGE (
parent DECIMAL(10, 0) NOT NULL,
child DECIMAL(10, 0) NOT NULL,
PRIMARY KEY (parent, child)
);
CREATE TABLE GRAPH_TC (
parent DECIMAL(10, 0) NOT NULL,
child DECIMAL(10, 0) NOT NULL,
refcount DECIMAL(9, 0),
PRIMARY KEY (parent, child)
);
CREATE TABLE GRAPH_TC_TEMP (
session_id DECIMAL(9, 0),
parent DECIMAL(10, 0),
child DECIMAL(10, 0)
);
CREATE PROCEDURE GRAPH_TC_CREATE (p_parent DECIMAL(10, 0), c_child DECIMAL(10, 0))
AS
declare variable tp_parent DECIMAL(10,0);
declare variable tc_child DECIMAL(10,0);
declare variable session_id DECIMAL(9,0);
declare variable refs DECIMAL(9,0);
begin
session_id = gen_id(graph_tc_seq,1);
insert into graph_tc_temp (parent, child, session_id, refcount) values (:p_parent, :p_parent, :session_id, 1);
insert into graph_tc_temp (parent, child, session_id, refcount) values (:c_child, :c_child, :session_id, 1);
insert into graph_tc_temp (parent, child, session_id, refcount) values (:p_parent, :c_child, :session_id, 1);
insert into graph_tc_temp (parent, child, session_id, refcount) select distinct :p_parent, child, :session_id, refcount from graph_tc where parent = :c_child and not parent = child;
insert into graph_tc_temp (child, parent, session_id, refcount) select distinct :c_child, parent, :session_id, refcount from graph_tc where child = :p_parent and not parent = child;
insert into graph_tc_temp (parent, child, session_id, refcount) select distinct a.parent, b.child, :session_id, a.refcount*b.refcount from graph_tc a, graph_tc b where a.child = :p_parent and b.parent = :c_child and not a.parent = a.child and not b.parent = b.child;
for select parent, child, refcount from graph_tc_temp e where session_id= :session_id and exists (select * from graph_tc t where t.parent = e.parent and t.child = e.child) into :tp_parent, :tc_child, :refs do begin
update graph_tc set refcount=refcount+ :refs where parent = :tp_parent and child = :tc_child;
end
insert into graph_tc (parent, child, refcount) select parent, child, refcount from graph_tc_temp e where session_id = :session_id and not exists (select * from graph_tc t where t.parent = e.parent and t.child = e.child);
delete from graph_tc_temp where session_id = :session_id;
end^
CREATE PROCEDURE GRAPH_TC_DELETE (p_parent DECIMAL(10, 0), c_child DECIMAL(10, 0))
AS
declare variable tp_parent DECIMAL(10,0);
declare variable tc_child DECIMAL(10,0);
declare variable refs DECIMAL(9,0);
begin
delete from graph_tc where parent = :p_parent and child = :p_parent and refcount <= 1;
update graph_tc set refcount = refcount - 1 where parent = :p_parent and child = :p_parent and refcount > 1;
delete from graph_tc where parent = :c_child and child = :c_child and refcount <= 1;
update graph_tc set refcount = refcount - 1 where parent = :c_child and child = :c_child and refcount > 1;
delete from graph_tc where parent = :p_parent and child = :c_child and refcount <= 1;
update graph_tc set refcount = refcount - 1 where parent = :p_parent and child = :c_child and refcount > 1;
for select distinct :p_parent, b.child, refcount from graph_tc b where b.parent = :c_child and not b.parent = b.child into :tp_parent, :tc_child, :refs do begin
delete from graph_tc where parent = :tp_parent and child = :tc_child and refcount <= :refs;
update graph_tc set refcount = refcount - :refs where parent = :tp_parent and child = :tc_child and refcount > :refs;
end
for select distinct :c_child, b.parent, refcount from graph_tc b where b.child = :p_parent and not b.parent = b.child into :tc_child, :tp_parent, :refs do begin
delete from graph_tc where child = :tc_child and parent = :tp_parent and refcount <= :refs;
update graph_tc set refcount = refcount - :refs where child = :tc_child and parent = :tp_parent and refcount > :refs;
end
for select distinct a.parent, b.child, a.refcount*b.refcount from graph_tc a, graph_tc b where not a.parent = a.child and not b.parent = b.child and a.child = :p_parent and b.parent = :c_child into :tp_parent, :tc_child, :refs do begin
delete from graph_tc where parent = :tp_parent and child = :tc_child and refcount <= :refs;
update graph_tc set refcount = refcount - :refs where parent = :tp_parent and child = :tc_child and refcount > :refs;
end
end^
CREATE TRIGGER GRAPH_TC_AFTER_INSERT FOR EDGE AFTER INSERT as
begin
execute procedure graph_tc_create(new.parent,new.child);
end^
CREATE TRIGGER GRAPH_TC_AFTER_UPDATE FOR EDGE AFTER UPDATE as
begin
if ((new.parent <> old.parent) or (new.child <> old.child)) then begin
execute procedure graph_tc_delete(old.parent,old.child);
execute procedure graph_tc_create(new.parent,new.child);
end
end^
CREATE TRIGGER GRAPH_TC_AFTER_DELETE FOR EDGE AFTER DELETE as
begin
execute procedure graph_tc_delete(old.parent,old.child);
end^
これは私の考えですが、他の人がすでにTCを実装していると思います。彼らは同じことをしていますか?
私はいくつかのテストケースを持っていますが、大きなグラフでは矛盾するかどうかはわかりません。
並行性については、2つの同時トランザクションがグラフを更新したい場合、このアプローチは失敗すると思いますか?
編集
私は自分のコード内のいくつかのバグを発見した、と私はあなたと固定されたバージョンを共有したいと思います。
私は素晴らしい記事を見つけました:http://www.codeproject.com/Articles/22824/A-Model-to-Represent-Directed-Acyclic-Graphs-DAG-o。異なるアプローチを使って、より興味深い論文や科学論文がありますか?
DDLとトリガ定義の(関連する部分)を含めることができますか? –
@MarkRotteveel私の編集を参照してください –
[GTT(グローバル一時テーブル)](http://www.firebirdsql.org/file/documentation/reference_manuals/reference_material/html/langrefupd25-ddl-table.html)を'GRAPH_TC_TEMP'の通常のテーブル –