MIME-Version: 1.0
From: SATYANARAYANA NARLAPURAM <satyanarlapuram@gmail.com>
Date: Fri, 10 Apr 2026 20:57:50 -0700
Message-ID: 
 <CAHg+QDfgK0xddH8f3eAb+UVn7sBDOnv8RvM6OkP4HtHAt6aD7w@mail.gmail.com>
Subject: Bug: Missing check_stack_depth() in GRAPH_TABLE rewriter
To: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>,
	Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>,
 Peter Eisentraut <peter@eisentraut.org>
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Hi Hackers,

Two recursive functions, generate_setop_from_pathqueries() and
generate_queries_for_path_pattern_recurse() in GRAPH_TABLE rewriter are
missing check_stack_depth() calls. Consider a property graph with  400 edge
tables with a 2-hop pattern produce 160,000 path queries and therefore
160,000 recursion frames in
generate_setop_from_pathqueries(). This can easily exceed the OS stack
limit for some systems and crashes the backend.

I am proposing a stop gap fix of checking stack depth by calling
check_stack_depth for now but in future we may want to reduce the recursion
depth (for example use a balanced tree to reduce depth from O(N) to O(log
N).

Attached a patch for adding the check_stack_depth() check.

Repro:

CREATE TABLE sv (id int PRIMARY KEY);
  INSERT INTO sv VALUES (1);

  DO $$
  BEGIN
    FOR i IN 1..400 LOOP
      EXECUTE format(
        'CREATE TABLE se_%s (id int PRIMARY KEY, src int, dst int)', i);
    END LOOP;
  END$$;

  DO $$
  DECLARE
    sql text;
    edges text := '';
  BEGIN
    FOR i IN 1..400 LOOP
      IF i > 1 THEN edges := edges || ', '; END IF;
      edges := edges || format(
        'se_%s KEY (id) SOURCE KEY (src) REFERENCES sv (id) '
        'DESTINATION KEY (dst) REFERENCES sv (id)', i);
    END LOOP;
    EXECUTE 'CREATE PROPERTY GRAPH g VERTEX TABLES (sv KEY (id)) '
         || 'EDGE TABLES (' || edges || ')';
  END$$;

  SELECT * FROM GRAPH_TABLE(g
    MATCH (a)-[e1]->(b)-[e2]->(c)
    COLUMNS(a.id AS a_id))
  LIMIT 1;

Thanks,
Satya

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<div dir=3D"ltr">Hi Hackers,<div><br></div><div>Two recursive functions, ge=
nerate_setop_from_pathqueries() and<br>generate_queries_for_path_pattern_re=
curse() in GRAPH_TABLE rewriter are missing check_stack_depth() calls. Cons=
ider a property graph with=C2=A0 400 edge tables with a 2-hop pattern produ=
ce 160,000 path queries and therefore 160,000 recursion frames in</div>gene=
rate_setop_from_pathqueries(). This can easily exceed the OS stack limit fo=
r some systems and crashes the backend.<div><br></div><div>I am proposing a=
 stop gap fix of checking stack depth by calling check_stack_depth for now =
but in future we may want to reduce the recursion depth (for example use a =
balanced tree to reduce depth from O(N) to O(log N).</div><div><br></div><d=
iv>Attached a patch for adding the=C2=A0check_stack_depth() check.</div><di=
v><br></div><div>Repro:</div><div><br></div><div>CREATE TABLE sv (id int PR=
IMARY KEY);<br>=C2=A0 INSERT INTO sv VALUES (1);<br><br>=C2=A0 DO $$<br>=C2=
=A0 BEGIN<br>=C2=A0 =C2=A0 FOR i IN 1..400 LOOP<br>=C2=A0 =C2=A0 =C2=A0 EXE=
CUTE format(<br>=C2=A0 =C2=A0 =C2=A0 =C2=A0 &#39;CREATE TABLE se_%s (id int=
 PRIMARY KEY, src int, dst int)&#39;, i);<br>=C2=A0 =C2=A0 END LOOP;<br>=C2=
=A0 END$$;<br><br>=C2=A0 DO $$<br>=C2=A0 DECLARE<br>=C2=A0 =C2=A0 sql text;=
<br>=C2=A0 =C2=A0 edges text :=3D &#39;&#39;;<br>=C2=A0 BEGIN<br>=C2=A0 =C2=
=A0 FOR i IN 1..400 LOOP<br>=C2=A0 =C2=A0 =C2=A0 IF i &gt; 1 THEN edges :=
=3D edges || &#39;, &#39;; END IF;<br>=C2=A0 =C2=A0 =C2=A0 edges :=3D edges=
 || format(<br>=C2=A0 =C2=A0 =C2=A0 =C2=A0 &#39;se_%s KEY (id) SOURCE KEY (=
src) REFERENCES sv (id) &#39;<br>=C2=A0 =C2=A0 =C2=A0 =C2=A0 &#39;DESTINATI=
ON KEY (dst) REFERENCES sv (id)&#39;, i);<br>=C2=A0 =C2=A0 END LOOP;<br>=C2=
=A0 =C2=A0 EXECUTE &#39;CREATE PROPERTY GRAPH g VERTEX TABLES (sv KEY (id))=
 &#39;<br>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0|| &#39;EDGE TABLES (&#39; || e=
dges || &#39;)&#39;;<br>=C2=A0 END$$;</div><div><br>=C2=A0 SELECT * FROM GR=
APH_TABLE(g<br>=C2=A0 =C2=A0 MATCH (a)-[e1]-&gt;(b)-[e2]-&gt;(c)<br>=C2=A0 =
=C2=A0 COLUMNS(<a href=3D"http://a.id">a.id</a> AS a_id))<br>=C2=A0 LIMIT 1=
;</div><div><br></div><div>Thanks,</div><div>Satya</div></div>

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