Как да поддържаме ефективно таблица за преходно затваряне?

Имам DAG в моята релационна база данни (Firebird) с две таблици edge и node (модел на списък със съседство). Искам да ги запитам рекурсивно, но намерих рекурсивните заявки за много неефективни. Така че се опитах да внедря тригери, за да поддържам транзитивното затваряне след Dong et.al. хартия http://homepages.inf.ed.ac.uk/libkin/papers/tc-sql.pdf.

SELECTs вече са много бързи, но DELETEs са изключително бавни, защото почти цялата графика се копира за едно изтриване. Дори по-лошо, едновременните актуализации изглеждат невъзможни.

Има ли по-добър начин за прилагане на това?

Редактиране

Направих няколко експеримента и въведох референтен брояч към таблицата TC. С това изтриванията са бързи. Написах няколко прости тестови случая, но не съм сигурен дали се справям правилно. Това е, което имам досега:

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 ^

Това е моя собствена идея, но мисля, че други вече са внедрили TC. Правят ли едно и също нещо?

Имам някои тестови случаи, но не съм сигурен дали може да получа несъответствие с по-големи графики.

Какво ще кажете за паралелността, мисля, че този подход ще се провали, когато две едновременни транзакции искат да актуализират графиката, нали?

Редактиране

Открих някои грешки в моя код и бих искал да споделя коригираната версия с вас.

Намерих страхотна статия: http://www.codeproject.com/Articles/22824/A-Model-to-Represent-Directed-Acyclic-Graphs-DAG-o. Има ли по-интересни статии или научни трудове с различни подходи?