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6Apr/140

Working with bit masks in T-SQL

Decoding bitwise masks can be a bit confusing, so I wanted to share a couple of T-SQL functions I've created to make them easier to deal with. If you'd like to read more about bitmasks and applying them in T-SQL, you can read about it at SQL Fool: T-SQL Bitwise Operators.

The first will return the value in a given bit position of an integer - it accepts two parameters (the lookup value and the bit position) and returns a bit for the value in that position. Note that it starts with position zero, so make sure you're counting correctly:

CREATE FUNCTION dbo.BitwisePosition(
	@value BIGINT,
	@PositionNumber INT
) RETURNS BIT
WITH SCHEMABINDING
AS
BEGIN

	DECLARE @Result BIT
	DECLARE @Mask BIGINT
		SET @Mask = POWER(2,@PositionNumber)

	SET @Result = (CASE @value & @Mask WHEN @Mask then 1 else 0 end)

	RETURN @Result

END
GO

The second function returns a bit (true/false) based on whether a provided bitmask applies to a reference value:

CREATE FUNCTION dbo.BitwiseMask(
	@value BIGINT,
	@Mask BIGINT
) RETURNS BIT
WITH SCHEMABINDING
AS
BEGIN

	DECLARE @Result BIT

	SET @Result = (CASE @value & @Mask WHEN @Mask then 1 else 0 end)

	RETURN @Result

END
GO

Don't forget to grant them permissions:

GRANT EXECUTE ON dbo.BitwiseMask TO PUBLIC
GRANT EXECUTE ON dbo.BitwisePosition TO PUBLIC

To use these functions, you'd call them as in these examples:

-- Value:   1110001000
-- Position 9876543210
-- Checkpoing position 7, 4, and 0 should return 1, 0, 0
 select dbo.bitwiseposition(904, 7),
		dbo.bitwiseposition(904, 4),
		dbo.bitwiseposition(904, 0)

-- Value:   1110001000 = 904
-- Bitmask: 0010001000 = 136
-- Will return true since mask "fits inside" value
select dbo.bitwisemask(904, 136)

-- Value:   1110001000 = 904
-- Bitmask: 0010001001 = 137
-- false since mask has a bit "outside" value
select dbo.bitwisemask(904, 137)

I hope you find them helpful!

3Apr/140

Oracle Goldengate REPLICAT frozen on “Starting”

We use Oracle Goldengate (expensive and probably overkill for Oracle->MSSQL, but good at what it does) to replicate data from an Oracle database into a SQL Server. However, I got an alert the other day that replication had stopped, and when I checked the status of replication, all the REPs we had set up were in status "Starting...", but none we actually doing anything.

Attempting to stop them got the following error:

GGSCI (GGSERVER) 68> stop rep MYREP
Sending STOP request to REPLICAT MYREP ...
ERROR: opening port for REPLICAT MYREP (TCP/IP error: Connection refused).

 

Stopping/Starting the manager service or rebooting the PC didn't help either - they still said "Starting" and were unresponsive. Even stranger, deleting and recreating the REP gave the same result - before I even attempted to start the REP for the first time, it said "Starting", and an attempt to start it gave me "Process is starting up - try again later".

The cause was the REP process status file, located in the DIRPCS folder under the Goldengate root - there should be a file for each REP that's currently running giving details about the status. When a REP stops, this file is deleted. Since all of the current REPs weren't doing anything (they were all sitting at the end of the previous trail file), they should have been stopped. I deleted the PCR files for the affected REP streams, and then manager reporting "STOPPED" - at that point, I was able to start up each REP without issue.

I'm not sure how they got that way, but once started again, they all worked without issue. I hope this saves you the troubleshooting time of hunting down these files!