Re: foreign key on delete cascade order?

[George Woodring <george.woodring@xxxxxxxxxx>]

On Thu, Mar 10, 2022 at 12:38 PM Tom Lane <tgl@xxxxxxxxxxxxx> wrote:

With the amount of detail you've provided (viz: none)

This is an example of the error we are seeing from our application. Sorry, I cannot find the postgresql log entry for this one.

2020-11-30T13:16:08,835 ERROR [foo/bar/01EF2.W01E/55159] GlobalControllerAdvice: Caught exception (https://noc.iglass.net/networkMachDelete.htm): org.springframework.dao.DeadlockLoserDataAccessException: PreparedStatementCallback; SQL [DELETE FROM mach WHERE (machid=?)]; ERROR: deadlock detected
  Detail: Process 27442 waits for ShareLock on transaction 1895244982; blocked by process 21064.
Process 21064 waits for ShareLock on transaction 1895245026; blocked by process 27442.
  Hint: See server log for query details.
  Where: while deleting tuple (5,18) in relation "status"
SQL statement "DELETE FROM ONLY "public"."status" WHERE $1 OPERATOR(pg_catalog.=) "pollid""; nested exception is org.postgresql.util.PSQLException: ERROR: deadlock detected
  Detail: Process 27442 waits for ShareLock on transaction 1895244982; blocked by process 21064.
Process 21064 waits for ShareLock on transaction 1895245026; blocked by process 27442.
  Hint: See server log for query details.
  Where: while deleting tuple (5,18) in relation "status"
SQL statement "DELETE FROM ONLY "public"."status" WHERE $1 OPERATOR(pg_catalog.=) "pollid""
org.springframework.dao.DeadlockLoserDataAccessException: PreparedStatementCallback; SQL [DELETE FROM mach WHERE (machid=?)]; ERROR: deadlock detected
  Detail: Process 27442 waits for ShareLock on transaction 1895244982; blocked by process 21064.
Process 21064 waits for ShareLock on transaction 1895245026; blocked by process 27442.
  Hint: See server log for query details.
  Where: while deleting tuple (5,18) in relation "status"
SQL statement "DELETE FROM ONLY "public"."status" WHERE $1 OPERATOR(pg_catalog.=) "pollid""; nested exception is org.postgresql.util.PSQLException: ERROR: deadlock detected
  Detail: Process 27442 waits for ShareLock on transaction 1895244982; blocked by process 21064.
Process 21064 waits for ShareLock on transaction 1895245026; blocked by process 27442.
  Hint: See server log for query details.
  Where: while deleting tuple (5,18) in relation "status"

SQL statement "DELETE FROM ONLY "public"."status" WHERE $1 OPERATOR(pg_catalog.=) "pollid"" 

The tables are involved are
CREATE TABLE mach ( machid serial, constraint mach_pkey primary key (machid) ... );

CREATE TABLE pollgrpinfo ( pollgrpid serial, constraint pollgrpinfo_pkey primary key (pollgrpid),
         machid    int4 NOT NULL, constraint mach_exists FOREIGN KEY(machid) REFERENCES mach ON DELETE CASCADE, ... );

CREATE TABLE poll ( pollid serial, constraint poll_pkey primary key (pollid),
        pollgrpid int4 not null, constraint pollgrp_exists FOREIGN KEY(pollgrpid) REFERENCES pollgrpinfo (pollgrpid) ON DELETE CASCADE, ...);

CREATE TABLE status ( statusid serial, constraint status_pkey primary key (statusid),
        pollid int4 not null, constraint poll_exists FOREIGN KEY(pollid) REFERENCES poll ON DELETE CASCADE, ...);

We are updating the entire status table every 5 minutes with

BEGIN;

UPDATE status SET () WHERE pollid = $1;

COMMIT;

The issue is arriving when some does a DELETE during the UPDATE of status

DELETE FROM mach WHERE machid=$1;

I don't know if this sheds any more light on it.

George

iGLASS Networks