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gregfelice
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claude
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Fix entity_exists() CID visibility for CREATE + WITH + MERGE (#2343)
* Fix entity_exists() CID visibility for CREATE + WITH + MERGE (#1954) When a Cypher query chains CREATE ... WITH ... MERGE, vertices created by CREATE become invisible to entity_exists() after a threshold number of input rows. This causes MERGE to throw "vertex assigned to variable was deleted". Root cause: CREATE calls CommandCounterIncrement() which advances the global command ID, but does not update es_snapshot->curcid. The Decrement/Increment CID macros used by the executors bring curcid back to the same value on each iteration. After enough rows, newly inserted vertices have a Cmin >= curcid and HeapTupleSatisfiesMVCC rejects them (requires Cmin < curcid). Fix: In entity_exists(), temporarily set es_snapshot->curcid to the current global command ID (via GetCurrentCommandId) for the duration of the scan, then restore it. This makes all entities inserted by preceding clauses in the same query visible to the existence check. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com> * Use Max() to prevent curcid regression in entity_exists() Address review feedback: es_snapshot->curcid can be ahead of the global CID due to Increment_Estate_CommandId macros. Unconditionally assigning GetCurrentCommandId(false) could decrease curcid, making previously visible tuples invisible. Use Max(saved_curcid, GetCurrentCommandId(false)) to ensure we only ever increase visibility. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com> --------- Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
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‎regress/expected/cypher_merge.out‎

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@@ -1865,6 +1865,114 @@ $$) AS (edge_count agtype);
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0
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(1 row)
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-- Issue 1954: CREATE + WITH + MERGE causes "vertex was deleted" error
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-- when the number of input rows exceeds the snapshot's command ID window.
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-- entity_exists() used a stale curcid, making recently-created vertices
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-- invisible on later iterations.
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--
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SELECT * FROM create_graph('issue_1954');
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NOTICE: graph "issue_1954" has been created
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create_graph
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--------------
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(1 row)
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-- Setup: create source nodes and relationships (3 rows to trigger the bug)
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SELECT * FROM cypher('issue_1954', $$
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CREATE (:A {name: 'a1'})-[:R]->(:B {name: 'b1'}),
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(:A {name: 'a2'})-[:R]->(:B {name: 'b2'}),
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(:A {name: 'a3'})-[:R]->(:B {name: 'b3'})
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$$) AS (result agtype);
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result
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--------
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(0 rows)
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-- This query would fail with "vertex assigned to variable c was deleted"
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-- on the 3rd row before the fix.
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SELECT * FROM cypher('issue_1954', $$
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MATCH (a:A)-[:R]->(b:B)
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CREATE (c:C {name: a.name + '|' + b.name})
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WITH a, b, c
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MERGE (a)-[:LINK]->(c)
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RETURN a.name, b.name, c.name
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ORDER BY a.name
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$$) AS (a agtype, b agtype, c agtype);
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a | b | c
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------+------+---------
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"a1" | "b1" | "a1|b1"
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"a2" | "b2" | "a2|b2"
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"a3" | "b3" | "a3|b3"
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(3 rows)
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-- Verify edges were created
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SELECT * FROM cypher('issue_1954', $$
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MATCH (a:A)-[:LINK]->(c:C)
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RETURN a.name, c.name
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ORDER BY a.name
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$$) AS (a agtype, c agtype);
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a | c
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------+---------
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"a1" | "a1|b1"
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"a2" | "a2|b2"
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"a3" | "a3|b3"
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(3 rows)
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-- Test with two MERGEs (more complex case from the original report)
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SELECT * FROM cypher('issue_1954', $$
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MATCH ()-[e:LINK]->() DELETE e
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$$) AS (result agtype);
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result
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--------
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(0 rows)
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SELECT * FROM cypher('issue_1954', $$
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MATCH (c:C) DELETE c
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$$) AS (result agtype);
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result
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--------
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(0 rows)
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SELECT * FROM cypher('issue_1954', $$
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MATCH (a:A)-[:R]->(b:B)
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CREATE (c:C {name: a.name + '|' + b.name})
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WITH a, b, c
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MERGE (a)-[:LINK1]->(c)
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MERGE (b)-[:LINK2]->(c)
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RETURN a.name, b.name, c.name
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ORDER BY a.name
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$$) AS (a agtype, b agtype, c agtype);
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a | b | c
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------+------+---------
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"a1" | "b1" | "a1|b1"
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"a2" | "b2" | "a2|b2"
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"a3" | "b3" | "a3|b3"
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(3 rows)
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-- Verify both sets of edges
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SELECT * FROM cypher('issue_1954', $$
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MATCH (a:A)-[:LINK1]->(c:C)
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RETURN a.name, c.name
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ORDER BY a.name
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$$) AS (a agtype, c agtype);
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a | c
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------+---------
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"a1" | "a1|b1"
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"a2" | "a2|b2"
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"a3" | "a3|b3"
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(3 rows)
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SELECT * FROM cypher('issue_1954', $$
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MATCH (b:B)-[:LINK2]->(c:C)
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RETURN b.name, c.name
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ORDER BY b.name
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$$) AS (b agtype, c agtype);
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b | c
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------+---------
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"b1" | "a1|b1"
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"b2" | "a2|b2"
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"b3" | "a3|b3"
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(3 rows)
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--
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-- clean up graphs
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--
@@ -1888,6 +1996,11 @@ SELECT * FROM cypher('issue_1446', $$ MATCH (n) DETACH DELETE n $$) AS (a agtype
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---
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(0 rows)
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SELECT * FROM cypher('issue_1954', $$ MATCH (n) DETACH DELETE n $$) AS (a agtype);
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a
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---
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(0 rows)
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--
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-- delete graphs
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--
@@ -1985,6 +2098,23 @@ NOTICE: graph "issue_1446" has been dropped
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(1 row)
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SELECT drop_graph('issue_1954', true);
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NOTICE: drop cascades to 9 other objects
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DETAIL: drop cascades to table issue_1954._ag_label_vertex
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drop cascades to table issue_1954._ag_label_edge
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drop cascades to table issue_1954."A"
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drop cascades to table issue_1954."R"
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drop cascades to table issue_1954."B"
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drop cascades to table issue_1954."C"
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drop cascades to table issue_1954."LINK"
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drop cascades to table issue_1954."LINK1"
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drop cascades to table issue_1954."LINK2"
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NOTICE: graph "issue_1954" has been dropped
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drop_graph
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------------
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(1 row)
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19882118
--
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-- End
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--

‎regress/sql/cypher_merge.sql‎

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Original file line numberDiff line numberDiff line change
@@ -860,13 +860,77 @@ SELECT * FROM cypher('issue_1446', $$
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RETURN count(*) AS edge_count
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$$) AS (edge_count agtype);
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-- Issue 1954: CREATE + WITH + MERGE causes "vertex was deleted" error
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-- when the number of input rows exceeds the snapshot's command ID window.
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-- entity_exists() used a stale curcid, making recently-created vertices
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-- invisible on later iterations.
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--
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SELECT * FROM create_graph('issue_1954');
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-- Setup: create source nodes and relationships (3 rows to trigger the bug)
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SELECT * FROM cypher('issue_1954', $$
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CREATE (:A {name: 'a1'})-[:R]->(:B {name: 'b1'}),
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(:A {name: 'a2'})-[:R]->(:B {name: 'b2'}),
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(:A {name: 'a3'})-[:R]->(:B {name: 'b3'})
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$$) AS (result agtype);
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-- This query would fail with "vertex assigned to variable c was deleted"
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-- on the 3rd row before the fix.
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SELECT * FROM cypher('issue_1954', $$
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MATCH (a:A)-[:R]->(b:B)
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CREATE (c:C {name: a.name + '|' + b.name})
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WITH a, b, c
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MERGE (a)-[:LINK]->(c)
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RETURN a.name, b.name, c.name
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ORDER BY a.name
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$$) AS (a agtype, b agtype, c agtype);
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-- Verify edges were created
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SELECT * FROM cypher('issue_1954', $$
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MATCH (a:A)-[:LINK]->(c:C)
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RETURN a.name, c.name
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ORDER BY a.name
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$$) AS (a agtype, c agtype);
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-- Test with two MERGEs (more complex case from the original report)
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SELECT * FROM cypher('issue_1954', $$
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MATCH ()-[e:LINK]->() DELETE e
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$$) AS (result agtype);
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SELECT * FROM cypher('issue_1954', $$
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MATCH (c:C) DELETE c
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$$) AS (result agtype);
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SELECT * FROM cypher('issue_1954', $$
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MATCH (a:A)-[:R]->(b:B)
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CREATE (c:C {name: a.name + '|' + b.name})
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WITH a, b, c
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MERGE (a)-[:LINK1]->(c)
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MERGE (b)-[:LINK2]->(c)
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RETURN a.name, b.name, c.name
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ORDER BY a.name
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$$) AS (a agtype, b agtype, c agtype);
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-- Verify both sets of edges
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SELECT * FROM cypher('issue_1954', $$
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MATCH (a:A)-[:LINK1]->(c:C)
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RETURN a.name, c.name
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ORDER BY a.name
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$$) AS (a agtype, c agtype);
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SELECT * FROM cypher('issue_1954', $$
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MATCH (b:B)-[:LINK2]->(c:C)
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RETURN b.name, c.name
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ORDER BY b.name
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$$) AS (b agtype, c agtype);
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--
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-- clean up graphs
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--
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SELECT * FROM cypher('cypher_merge', $$ MATCH (n) DETACH DELETE n $$) AS (a agtype);
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SELECT * FROM cypher('issue_1630', $$ MATCH (n) DETACH DELETE n $$) AS (a agtype);
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SELECT * FROM cypher('issue_1709', $$ MATCH (n) DETACH DELETE n $$) AS (a agtype);
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SELECT * FROM cypher('issue_1446', $$ MATCH (n) DETACH DELETE n $$) AS (a agtype);
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SELECT * FROM cypher('issue_1954', $$ MATCH (n) DETACH DELETE n $$) AS (a agtype);
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--
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-- delete graphs
@@ -877,6 +941,7 @@ SELECT drop_graph('issue_1630', true);
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SELECT drop_graph('issue_1691', true);
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SELECT drop_graph('issue_1709', true);
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SELECT drop_graph('issue_1446', true);
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SELECT drop_graph('issue_1954', true);
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881946
--
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-- End

‎src/backend/executor/cypher_utils.c‎

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Original file line numberDiff line numberDiff line change
@@ -208,6 +208,7 @@ bool entity_exists(EState *estate, Oid graph_oid, graphid id)
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HeapTuple tuple;
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Relation rel;
210210
bool result = true;
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CommandId saved_curcid;
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212213
/*
213214
* Extract the label id from the graph id and get the table name
@@ -219,6 +220,23 @@ bool entity_exists(EState *estate, Oid graph_oid, graphid id)
219220
ScanKeyInit(&scan_keys[0], 1, BTEqualStrategyNumber,
220221
F_GRAPHIDEQ, GRAPHID_GET_DATUM(id));
221222

223+
/*
224+
* Temporarily advance the snapshot's curcid so that entities inserted
225+
* by preceding clauses (e.g., CREATE) in the same query are visible.
226+
* CREATE calls CommandCounterIncrement() which advances the global
227+
* CID, but does not update es_snapshot->curcid. The Decrement/Increment
228+
* CID macros used by the executors can leave curcid behind the global
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* CID, making recently created entities invisible to this scan.
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*
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* Use Max to ensure we never decrease curcid. The executor macros
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* (Increment_Estate_CommandId) can push curcid above the global CID,
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* and blindly assigning GetCurrentCommandId could make tuples that
234+
* are visible at the current curcid become invisible.
235+
*/
236+
saved_curcid = estate->es_snapshot->curcid;
237+
estate->es_snapshot->curcid = Max(saved_curcid,
238+
GetCurrentCommandId(false));
239+
222240
rel = table_open(label->relation, RowExclusiveLock);
223241
scan_desc = table_beginscan(rel, estate->es_snapshot, 1, scan_keys);
224242

@@ -236,6 +254,9 @@ bool entity_exists(EState *estate, Oid graph_oid, graphid id)
236254
table_endscan(scan_desc);
237255
table_close(rel, RowExclusiveLock);
238256

257+
/* Restore the original curcid */
258+
estate->es_snapshot->curcid = saved_curcid;
259+
239260
return result;
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}
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