PostgreSQL error: EXECUTE query string argument is null

Question

I have a table called proof with a trigger that calls a stored procedure that basically divides the tables by month. However, I get an unclear error when I start inserting many lines under load:

Npgsql.NpgsqlException: query string argument of EXECUTE is null 
Severity: ERROR Code: 22004 at Npgsql.NpgsqlState.<ProcessBackendResponses_Ver_3>d__a.MoveNext() in c:\C#Apps\github.npgsql.Npgsql.stock\src\Npgsql\NpgsqlState.cs:line890 at Npgsql.ForwardsOnlyDataReader.GetNextResponseObject() in c:\C#Apps\github.npgsql.Npgsql.stock\src\Npgsql\NpgsqlDataReader.cs:line 1175 at 
    Npgsql.ForwardsOnlyDataReader.GetNextRowDescription() in c:\C#Apps\github.npgsql.Npgsql.stock\src\Npgsql\NpgsqlDataReader.cs:line 1191    at 
    Npgsql.ForwardsOnlyDataReader.NextResult() in c:\C#Apps\github.npgsql.Npgsql.stock\src\Npgsql\NpgsqlDataReader.cs:line 1377    at 
    Npgsql.NpgsqlCommand.ExecuteNonQuery() in c:\C#Apps\github.npgsql.Npgsql.stock\src\Npgsql\NpgsqlCommand.cs:line523

My system has an automatic repeat function, and as a result, each record is inserted into the database, but after many many exceptions, when the load is high.

The database is PostgreSQL 9.3 on the CentOS 6 server, and the client is C # .NET using the Npgsql driver.

Table:

CREATE TABLE evidence
(
  id uuid NOT NULL,
  notification_id uuid NOT NULL,
  feedback character varying(200),
  result character varying(20),
  trigger_action_type character varying(200),
  trigger_action_id uuid,
  data_type integer NOT NULL,
  data bytea,
  name character varying(30),
  CONSTRAINT pk_evidence PRIMARY KEY (id)
);

Trigger:

CREATE TRIGGER evidence_move_to_partition_tables
  BEFORE INSERT
  ON evidence
  FOR EACH ROW
  EXECUTE PROCEDURE partition_evidence_by_month();

Trigger function:

CREATE OR REPLACE FUNCTION partition_evidence_by_month()
  RETURNS trigger AS
$BODY$
DECLARE 
    _notification_id uuid;
    _raised_local_time timestamp without time zone;
    _table_name character varying(35);
    _start_date timestamp without time zone;
    _end_date timestamp without time zone;
    _table_space character varying(50) := 'ls_tablespace2';
    _query text;
BEGIN
    _notification_id := NEW.notification_id;
    SELECT raised_local_time FROM notifications WHERE id=_notification_id INTO _raised_local_time;
    _start_date := date_trunc('month', _raised_local_time);
    _end_date   := _start_date + '1 month'::interval;
    _table_name := 'evidence-' || to_char(_start_date, 'YYYY-MM');

    -- check to see if table already exists
    PERFORM 1
    FROM   pg_catalog.pg_class c
    JOIN   pg_catalog.pg_namespace n ON n.oid = c.relnamespace
    WHERE  c.relkind = 'r'
    AND    c.relname = _table_name
    AND    n.nspname = 'public';

    -- if the table doesn't exist, then create it now
    IF NOT FOUND THEN
        -- create partition table
        _query := 'CREATE TABLE public.' || quote_ident(_table_name) || ' ( ) INHERITS (public.evidence)';
        EXECUTE _query;
        -- alter owner
        --EXECUTE 'ALTER TABLE public.' || quote_ident(_table_name) || ' OWNER TO postgres';
        -- add index
        --EXECUTE 'ALTER TABLE public.' || quote_ident(_table_name) || ' ADD PRIMARY KEY (id)';
    END IF;
    -- move the data to the partition table
    EXECUTE 'INSERT INTO public.' || quote_ident(_table_name) || ' VALUES ($1.*)' USING NEW;
    RETURN NULL;
END;
$BODY$ LANGUAGE plpgsql VOLATILE COST 100;

Call Code:

using (var cmd = db.CreateCommand())
{
    cmd.CommandText = @"INSERT INTO evidence   
    (id, notification_id, feedback, result, trigger_action_type, 
     trigger_action_id, data_type, data, name) 
    VALUES (@id,@nid,@feedback,@result,@tat,@taid,@dt,@data,@name)";
    cmd.Parameters.AddWithValue("@id", evItem.ID);
    cmd.Parameters.AddWithValue("@nid", evItem.NotificationID);
    cmd.Parameters.AddWithValue("@feedback", evItem.Feedback);
    cmd.Parameters.AddWithValue("@result", evItem.Result);
    cmd.Parameters.AddWithValue("@tat", evItem.TriggerActionType);
    cmd.Parameters.AddWithValue("@taid", evItem.TriggerActionID);
    cmd.Parameters.AddWithValue("@dt", (int)evItem.DataType);
    cmd.Parameters.AddWithValue("@data", evItem.Data);
    cmd.Parameters.AddWithValue("@name", evItem.Name);
    cmd.ExecuteNonQuery();
}

Why does this bizarre error appear only when the system is under load? What can I do to prevent this from happening?

Thank!

Answer 1

EXECUTE null

EXECUTE:

_query := 'CREATE TABLE public.'
        || quote_ident(_table_name) || ' ( ) INHERITS (public.evidence)';
EXECUTE _query;

...

EXECUTE 'INSERT INTO public.'
      || quote_ident(_table_name) || ' VALUES ($1.*)' USING NEW;

, NULL, table_name.
table_name NULL :

SELECT raised_local_time FROM notifications WHERE id=_notification_id
INTO _raised_local_time;

, :

• NEW.notification_id NULL.

• NEW.notification_id notifications.

:

CREATE OR REPLACE FUNCTION partition_evidence_by_month()
  RETURNS trigger AS
$func$
DECLARE 
   _table_name text;
BEGIN
   SELECT 'evidence-' || to_char(raised_local_time, 'YYYY-MM')
   FROM   public.notifications -- schema-qualify to be sure
   WHERE  id = NEW.notification_id
   INTO   _table_name;

   IF _table_name IS NULL THEN
      RAISE EXCEPTION '_table_name is NULL. Should not occur!';
   END IF;

   IF NOT EXISTS (   -- create table if it does not exist
      SELECT 1
      FROM   pg_catalog.pg_class c
      JOIN   pg_catalog.pg_namespace n ON n.oid = c.relnamespace
      WHERE  c.relkind = 'r'
      AND    c.relname = _table_name
      AND    n.nspname = 'public') THEN

      EXECUTE 'CREATE TABLE public.'
            || quote_ident(_table_name) || ' ( ) INHERITS (public.evidence)';
   END IF;

   EXECUTE 'INSERT INTO public.'
         || quote_ident(_table_name) || ' VALUES $1'  -- Use NEW row directly
   USING  NEW;       -- write data to the partition table

   RETURN NULL;
END
$func$ LANGUAGE plpgsql;

• . (, , .)

  • , date_trunc() . to_char().

  • varchar(n). text varchar.

  • , - PL/pgSQL.

• RAISE, . , . ...