Safely Selecting the Last Inserted ID, Part II

Well, as it turns out, this isn’t
an issue at all. I ran two tests. The first followed these steps:

  1. Using a CFQUERY tag, I executed an insert statement.
  2. Used Thread.sleep() to make the page hang for 10 seconds.
  3. Inserted ten additional rows from the command line (using the MySQL command
    line tool).
  4. After the Thread.sleep(), used LAST_INSERT_ID() to get the last inserted ID,
    and displaed it.

I expected the result to be 11, but it was actually 1.  The 10 rows I inserted
between the initial insert and when I selected the last inserted ID had no effect.  I
figured this was because ColdFusion was considered one client, and the command
line administrator was considered a different client, and since the scope of
the last inserted ID is the client/connection, I was protected.  So I ran this
test, instead:

  1. Executed an insert statement in ColdFusion.
  2. Slept for 10 seconds.
  3. Ran a second CFM page that inserted 10 rows while the first page was hung.
  4. After the thread in the original page woke up, selected the last inserted id
    and displayed it.

Keep in mind I was using no transactions or locks since I was trying to get a
wrong result before trying to figure out how to get the correct one, however
the result was once again 1.  As it turns out, no transactions or locks are
needed.  Why?  Apparently because each request gets its own database connection,
and that one connection gets reused for the duration for the request, regardless
of how many database operations you perform.  Other
requests can happen simultanously, of course, but they all get their own connections,
and hense do not affect the first connection’s last inserted ID value.  In
other words, it seems to work exactly how you would want it to!  ColdFusion
does it again!

Disclaimer: This test was run using JRun, CFMX 6.1 (with the
latest updater) and MySQL
version 4.0.18.  Before you rely on this data, you might want to run some tests
yourself, though I will try to get confirmation from the ColdFusion team that
this technique should work across all databases and future versions of ColdFusion.