Re: Where's my Derby?

On Wed, 07 Apr 2010 21:11:01 +0000, Andreas Leitgeb wrote:


That was me being cautious since we don't know what DBMS the OP has in
mind. For the following code to work the DBMS *must* support explicit
transaction control, serialised transaction mode and (probably) the
ability to set the lock timeout period. If we have all that the code is
straight forward:

set_session_conditions
{
  set auto-commit off;
  set transaction serialisation;
  set lock timeout = 5 seconds; // needs to be at least 2x the max
                                 // transaction execution time.
}

add_entry
{
  start transaction // may be implied
  select count(*) from table where key='?'
  if (count == zero)
     insert into table (key, value) values ('?', '?');
  commit
}