我的关系数据库（Firebird）中有一个 DAG，有两个表edge和node（邻接列表模型）。我想递归地查询它们，但发现递归查询效率很低。所以我尝试实现触发器来维持 Dong et.al 之后的传递闭包。论文http://homepages.inf.ed.ac.uk/libkin/papers/tc-sql.pdf。
SELECTs 现在非常快，但DELETEs 非常慢，因为几乎整个图形都被复制以进行一次删除。更糟糕的是，并发更新似乎是不可能的。
有没有更好的方法来实现这一点？
编辑
我做了一些实验，并为 TC 表引入了一个引用计数器。这样，删除速度很快。我写了一些简单的测试用例，但我不确定我是否做得对。这是我到目前为止所拥有的：
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 ^
这是我自己的想法，但我认为其他人已经实施了 TC。他们在做同样的事情吗？
我有一些测试用例，但我不确定我是否会与更大的图表不一致。
并发性怎么样，我认为当两个同时的事务想要更新图表时，这种方法会失败，对吧？
编辑
我在我的代码中发现了一些错误，我想与你分享修复版本。
我发现了一篇很棒的文章： http: //www.codeproject.com/Articles/22824/A-Model-to-Represent-Directed-Acyclic-Graphs-DAG-o。是否有更多有趣的文章或科学论文，采用不同的方法？