OLE DB provider "MSDASQL" for linked server "[name]" was unable to begin a distributed transaction

Question

I have a linked server setup from SQL Server Ent 2012 to PostgreSQL 9.3 and a stored procedure pulling 3 filtered tables from it and storing each in a temporary table.

There is a final query at the end of the Stored Procedure with many left joins, from local SQL Database and it includes these 3 temporary tables.
I have disabled "Enable promotion of distributed transactions for RPC". Every 1/6 or more attempts to use this Stored Procedure fails, with error on web server as: Unknown Error Detected System.Data.SqlClient.SqlException (0x80131904): The operation could not be performed because OLE DB provider "MSDASQL" for linked server "POSTGRESQL" was unable to begin a distributed transaction. at System.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolean breakConnection No errors on the SQL Server though.

Linked server definition:

EXEC master.dbo.sp_addlinkedserver @server = N'POSTGRESQL', @srvproduct=N'PostgreSQL', @provider=N'MSDASQL', @datasrc=N'PostgreSQL'
 EXEC master.dbo.sp_addlinkedsrvlogin @rmtsrvname=N'POSTGRESQL',@useself=N'False',@locallogin=NULL,@rmtuser=N'xxxxxx',@rmtpassword='xxxxx'
EXEC master.dbo.sp_serveroption @server=N'POSTGRESQL', @optname=N'collation compatible', @optvalue=N'false'
EXEC master.dbo.sp_serveroption @server=N'POSTGRESQL', @optname=N'data access', @optvalue=N'true'
EXEC master.dbo.sp_serveroption @server=N'POSTGRESQL', @optname=N'dist', @optvalue=N'false'
EXEC master.dbo.sp_serveroption @server=N'POSTGRESQL', @optname=N'pub', @optvalue=N'false'
EXEC master.dbo.sp_serveroption @server=N'POSTGRESQL', @optname=N'rpc', @optvalue=N'true'
EXEC master.dbo.sp_serveroption @server=N'POSTGRESQL', @optname=N'rpc out', @optvalue=N'true'
EXEC master.dbo.sp_serveroption @server=N'POSTGRESQL', @optname=N'sub', @optvalue=N'false'
EXEC master.dbo.sp_serveroption @server=N'POSTGRESQL', @optname=N'connect timeout', @optvalue=N'0'
EXEC master.dbo.sp_serveroption @server=N'POSTGRESQL', @optname=N'collation name', @optvalue=null
EXEC master.dbo.sp_serveroption @server=N'POSTGRESQL', @optname=N'lazy schema validation', @optvalue=N'false'
EXEC master.dbo.sp_serveroption @server=N'POSTGRESQL', @optname=N'query timeout', @optvalue=N'0'
EXEC master.dbo.sp_serveroption @server=N'POSTGRESQL', @optname=N'use remote collation', @optvalue=N'true'
EXEC master.dbo.sp_serveroption @server=N'POSTGRESQL', @optname=N'remote proc transaction promotion', @optvalue=N'false'

Stored Procedure/Query (very simplified sorry)

ALTER PROCEDURE [dbo].[SP_Name]
@DateFrom DATETIME,
@DateTo DATETIME

AS

DECLARE @variableB int

SET @variableB= {some criteria} 

IF (@variableB < 1000)

BEGIN
-- Passthrough to PG for a filtered table, instead of entire table grabbed via open query
    IF OBJECT_ID('tempdb.dbo.#temp_table1', 'U') IS NOT NULL
      DROP TABLE #temp_table1; 

    create table #temp_table1 (column1 int, column2 varchar(60))

    DECLARE @TSQL varchar(max)
    SET  @TSQL = 'select c1, c2 from OpenQuery([POSTGRESQL],''
            select c1, c2 from table1 t where 
            t.date>=''''' +CONVERT(VARCHAR(15),@DateFrom,102)+ '''''' + 't.date <=''''' +CONVERT(VARCHAR(15),@DateTo,102) + '''''' +'order by c1'')'

    insert into #temp_table1
    EXEC (@TSQL)

    create clustered index temp_index1 on #temp_table1 
    (column1 asc)
    WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, DROP_EXISTING = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON, FILLFACTOR = 90) ON [PRIMARY]

-- 2nd table passthrough to PG for a filtered table, instead of entire table grabbed via open query
    IF OBJECT_ID('tempdb.dbo.#temp_table2', 'U') IS NOT NULL
      DROP TABLE temp_table2; 

    create table #temp_table2 (column1 int, column2 varchar(60), column3 int)

    SET  @TSQL = 'select a, b, c from OpenQuery([POSTGRESQL],''
            select a, b, c from table2 t where 
            t.date>=''''' +CONVERT(VARCHAR(15),@DateFrom,102)+ '''''' + 't.date <=''''' +CONVERT(VARCHAR(15),@DateTo,102) + '''''' +'order by a'')'

    insert into #temp_table2
    EXEC (@TSQL)

-- 3rd table passthrough to PG for a filtered table, instead of entire table grabbed via open query
    IF OBJECT_ID('tempdb.dbo.#temp_table3', 'U') IS NOT NULL
      DROP TABLE temp_table3; 

    create table #temp_table3 (column1 int, column2 varchar(60))

    SET  @TSQL = 'select a1, a2, a3 from OpenQuery([POSTGRESQL],''
            select a1, a2, a3 
            from
            table3 t
            where 
            t.date>=''''' +CONVERT(VARCHAR(15),@DateFrom,102)+ '''''' + 't.date <=''''' +CONVERT(VARCHAR(15),@DateTo,102) + ''''''
{plus other filtering criteria} +'order by a1'')'

    insert into #temp_table2
    EXEC (@TSQL)

IF (@variableB < 1000)

BEGIN

select {many columns}
from {various local tables with left joins}
left join #temp_table1 on {conditions}
left join #temp_table2 on {conditions}
left join #temp_table3 on {conditions}

END

Local DTC Properties

• What I think is happening, is that the 3 openqueries into temp tables are getting distributed, and somehow that just doesn't work. I confess I don't understand this very well - it's over my head. I also know that enabling "Enable promotion of distributed transactions for RPC" makes the fails happen more frequently.
• This again works 5/6 times and fails about 1/6 times. So I am not sure what is happening.
• This is a read only transaction on PostgreSQL - I am not sure why distributed transaction is getting invoked at all.

Edit I see this question here and thinking I shouldn't be having this issue.

Edit 2 I may have a found a duplicate question here.

Answer 1

Wrapping the 3 temp table inserts in one transaction with ISOLATION LEVEL READ UNCOMMITTED seems to have stopped promotion to a distributed transaction and solved my intermittent problem.

SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;
BEGIN TRANSACTION;

    DECLARE @TSQL varchar(max)
    SET  @TSQL = 'select c1, c2 from OpenQuery([POSTGRESQL],''
            select c1, c2 from table1 t where 
            t.date>=''''' +CONVERT(VARCHAR(15),@DateFrom,102)+ '''''' + 't.date <=''''' +CONVERT(VARCHAR(15),@DateTo,102) + '''''' +'order by c1'')'

    insert into #temp_table1
    EXEC (@TSQL)

.....etc

COMMIT TRANSACTION;

This was a duplicate question and ultimately gave me the solution. Perhaps, PostgreSQL ODBC does not support distributed transactions - and disabling them on Linked Server Properties is not enough when attempting to use temp tables or attempting to connect to a remote database 3 times -- due to ACID functionality..