Pracuję z postgres 9.1 i otrzymuję wyjątek zakleszczenia w przypadku nadmiernego wykonywania prostej metody aktualizacji.

Według dzienników zakleszczenie występuje w wyniku wykonania dwóch identycznych aktualizacji w tym samym czasie.

aktualizacja public.vm_action_info set last_on_demand_task_id = 1 $, wersja = wersja + 1

Jak dwie identyczne proste aktualizacje mogą się wzajemnie zakleszczyć?

Błąd, który dostaję w dzienniku

2013-08-18 11:00:24 IDT HINT:  See server log for query details.
2013-08-18 11:00:24 IDT STATEMENT:  update public.vm_action_info set last_on_demand_task_id=$1, version=version+1 where id=$2
2013-08-18 11:00:25 IDT ERROR:  deadlock detected
2013-08-18 11:00:25 IDT DETAIL:  Process 31533 waits for ShareLock on transaction 4228275; blocked by process 31530.
        Process 31530 waits for ExclusiveLock on tuple (0,68) of relation 70337 of database 69205; blocked by process 31533.
        Process 31533: update public.vm_action_info set last_on_demand_task_id=$1, version=version+1 where id=$2
        Process 31530: update public.vm_action_info set last_on_demand_task_id=$1, version=version+1 where id=$2
2013-08-18 11:00:25 IDT HINT:  See server log for query details.
2013-08-18 11:00:25 IDT STATEMENT:  update public.vm_action_info set last_on_demand_task_id=$1, version=version+1 where id=$2
2013-08-18 11:00:25 IDT ERROR:  deadlock detected
2013-08-18 11:00:25 IDT DETAIL:  Process 31530 waits for ExclusiveLock on tuple (0,68) of relation 70337 of database 69205; blocked by process 31876.
        Process 31876 waits for ShareLock on transaction 4228275; blocked by process 31530.
        Process 31530: update public.vm_action_info set last_on_demand_task_id=$1, version=version+1 where id=$2
        Process 31876: update public.vm_action_info set last_on_demand_task_id=$1, version=version+1 where id=$2

schemat to:

CREATE TABLE vm_action_info(
  id integer NOT NULL,
  version integer NOT NULL DEFAULT 0,
  vm_info_id integer NOT NULL,
 last_exit_code integer,
  bundle_action_id integer NOT NULL,
  last_result_change_time numeric NOT NULL,
  last_completed_vm_task_id integer,
  last_on_demand_task_id bigint,
  CONSTRAINT vm_action_info_pkey PRIMARY KEY (id ),
  CONSTRAINT vm_action_info_bundle_action_id_fk FOREIGN KEY (bundle_action_id)
      REFERENCES bundle_action (id) MATCH SIMPLE
      ON UPDATE NO ACTION ON DELETE CASCADE,
  CONSTRAINT vm_discovery_info_fk FOREIGN KEY (vm_info_id)
      REFERENCES vm_info (id) MATCH SIMPLE
      ON UPDATE NO ACTION ON DELETE CASCADE,
  CONSTRAINT vm_task_last_on_demand_task_fk FOREIGN KEY (last_on_demand_task_id)
      REFERENCES vm_task (id) MATCH SIMPLE
      ON UPDATE NO ACTION ON DELETE NO ACTION,

  CONSTRAINT vm_task_last_task_fk FOREIGN KEY (last_completed_vm_task_id)
      REFERENCES vm_task (id) MATCH SIMPLE
      ON UPDATE NO ACTION ON DELETE NO ACTION
)
WITH (OIDS=FALSE);

ALTER TABLE vm_action_info
  OWNER TO vadm;

-- Index: vm_action_info_vm_info_id_index

-- DROP INDEX vm_action_info_vm_info_id_index;

CREATE INDEX vm_action_info_vm_info_id_index
  ON vm_action_info
  USING btree (vm_info_id );

CREATE TABLE vm_task
(
  id integer NOT NULL,
  version integer NOT NULL DEFAULT 0,
  vm_action_info_id integer NOT NULL,
  creation_time numeric NOT NULL DEFAULT 0,
  task_state text NOT NULL,
  triggered_by text NOT NULL,
  bundle_param_revision bigint NOT NULL DEFAULT 0,
  execution_time bigint,
  expiration_time bigint,
  username text,
  completion_time bigint,
  completion_status text,
  completion_error text,
  CONSTRAINT vm_task_pkey PRIMARY KEY (id ),
  CONSTRAINT vm_action_info_fk FOREIGN KEY (vm_action_info_id)
  REFERENCES vm_action_info (id) MATCH SIMPLE
  ON UPDATE NO ACTION ON DELETE CASCADE
)
 WITH (
OIDS=FALSE
);
ALTER TABLE vm_task
  OWNER TO vadm;

-- Index: vm_task_creation_time_index

-- DROP INDEX vm_task_creation_time_index     ;

CREATE INDEX vm_task_creation_time_index
  ON vm_task
  USING btree
 (creation_time );