I’m working on an article for conflict detection/resolution when using MySQL Cluster asynchronous replication which requires an integer column to store a timestamp for comparison purposes. In fact, it doesn’t actually need the timestamp to represent an absolute or even a relative point in time – all it cares about is that the if the function is called twice on 2 different hosts that the 2nd call will always result in a larger number than the 1st. Obviously, in a production environment the times on the 2 hosts would need to be kept in sync.

The c code (inttime.c)

#include <mysql.h>
#include <sys/time.h>

my_bool inttime_init(UDF_INIT *initid,UDF_ARGS *args, char *message) {
  return 0;
}

void inttime_deinit(UDF_INIT *initid) {};

unsigned long int inttime(UDF_INIT *initid, UDF_ARGS *args, char *result,
                          unsigned long  *length, char *is_null, char *error)
{
  struct timeval tv;
  gettimeofday(&tv,(void *)0);
  return ((double)tv.tv_usec)+tv.tv_sec*1000000;
}

Compiling and deploying the shared library

[billy@ws1 timestamp]$ gcc -I/usr/local/mysql/include/ -fPIC -shared -o inttime.so inttime.c
[billy@ws1 timestamp]$ cp inttime.so /usr/local/mysql/lib/plugin/

Creating the function

mysql> create function inttime RETURNS REAL SONAME 'inttime.so';

Test the function

mysql> select inttime();select inttime();
+------------------+
| inttime()        |
+------------------+
| 1250080524270706 |
+------------------+
1 row in set (0.00 sec)

+------------------+
| inttime()        |
+------------------+
| 1250080524270833 |
+------------------+
1 row in set (0.00 sec)

Note that the results are different and the second result is always larger than the first – function is fit for purpose

Using the function from a stored procedure

mysql> CREATE TRIGGER updateTAB1 BEFORE UPDATE ON TAB1 FOR EACH ROW SET NEW.ts = inttime();

Acknowledgements

I used the c code found at http://lists.mysql.com/internals/33702 as the starting point.