[I] `EXISTS { }` in a `WHERE` after a write clause crashes (segfault) the backend [age]

["hkjiang26 (via GitHub)" <gi...@apache.org>]

hkjiang26 opened a new issue, #2509:
URL: https://github.com/apache/age/issues/2509

   ## Bug description
   
   Writing a Cypher query in which a write clause (`CREATE`, `MERGE`, or `SET`) is followed by a `WITH` projection whose `WHERE` clause contains an `EXISTS { }` subquery crashes the PostgreSQL backend with a segmentation fault. The backend process is terminated (`signal 11: Segmentation fault`) and the connection is dropped. The crash happens even when the `EXISTS` subquery is empty and does not reference any outer variable, and even when the created vertex is not carried through the `WITH`.
   
   ## Access method
   
   - Command line via `psql`, inside the official Docker container `apache/age:1.8.0`
   
   ## Data setup
   
   No data is required — the crash reproduces on an empty graph. Only the graph itself must exist:
   
   ```pgsql
   CREATE EXTENSION IF NOT EXISTS age;
   LOAD 'age';
   SET search_path = ag_catalog, "$user", public;
   SELECT create_graph('graph_test');
   ```
   
   ## Configuration
   
   - None beyond the stock AGE extension. No additional modules (no PostGIS, etc.), default `search_path` handling as shown above.
   
   ## Command that triggers the crash
   
   ```pgsql
   SELECT * FROM cypher('graph_test', $$ CREATE (a) WITH a WHERE exists { RETURN 1 } RETURN 1 $$) AS (c0 agtype);
   ```
   
   The `CREATE` writes a single vertex, the `WITH` carries it forward, and the `WHERE`'s `EXISTS` subquery always yields one row. Any one of the following also crashes: using `MERGE (a)` or `MATCH (a) SET a.x = 1` instead of `CREATE (a)`; using `WITH *` or dropping `a` from the projection (`CREATE (a) WITH 1 AS x`); replacing the subquery body with `WITH a` or `RETURN a`.
   
   ```
   server closed the connection unexpectedly
   	This probably means the server terminated abnormally
   	before or while processing the request.
   connection to server was lost
   ```
   
   The server log shows the backend being killed:
   
   ```
   LOG:  client backend (PID NNN) was terminated by signal 11: Segmentation fault
   LOG:  terminating any other active server processes
   LOG:  all server processes terminated; reinitializing
   ```
   
   ## Expected behavior
   
   The query is valid Cypher: a write clause, a `WITH` projection, and an `EXISTS` subquery in a `WHERE` clause are all standard, and the subquery always returns one row. It should either execute normally or raise a normal Cypher error — it must not crash the backend process. Notably, the same `EXISTS` subquery in a `WHERE` attached to a pure read clause (e.g. `MATCH (a) WHERE exists { RETURN 1 } RETURN 1`) or in a `RETURN` projection (e.g. `RETURN exists { RETURN 1 }`) executes correctly; the crash is specific to the combination of a write clause feeding the `WITH` whose `WHERE` contains the `EXISTS`.
   
   ## Environment
   
   - Version: 1.8.0 (official `apache/age:1.8.0` Docker image)
   - PostgreSQL: 18.1 (Debian 18.1-1.pgdg13+2), x86_64
   


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Re: [I] `EXISTS { }` in a `WHERE` after a write clause crashes (segfault) the backend [age]

["hkjiang26 (via GitHub)" <gi...@apache.org>]

hkjiang26 closed issue #2509: `EXISTS { }` in a `WHERE` after a write clause crashes (segfault) the backend
URL: https://github.com/apache/age/issues/2509


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