Randy Letness skrev:
A little more info:
I have a test program with a "writer thread", a thread that
continuously performs update transactions, and a "reader thread", a
thread that does selects on the data that is being updated. So with
two threads, there should be at most 2 transactions in progress at any
instant. When the deadlock occurs, the lock dump table shows
otherwise. There are 3 distinct transaction ids (1,2,3 for
simplicity). Looking at the locks, I can tell that tx1 and tx3 are
update transactions (they have exclusive locks) and tx2 is the read tx
(has shared locks). This doesn't make sense because there is only a
single thread doing updates so there should only be a single update
transaction active. Tx2 is waiting on a lock held by tx1 and tx3 is
waiting on a lock held by tx2. For some reason the locks held by tx1
aren't released, and that is why the deadlock occurs. Its almost as
if the locks from the update transaction aren't being fully released
after a commit. Tx1 isn't waiting on anything, but the locks are
still there. So something screwy is going on. Is there such thing as
a phantom lock?
Also, I can't reproduce this on a MySQL database. I'm using the same
code, different JDBC driver.
Hello Randy,
I recommend you log a Jira issue with a simple reproduction
script/program. Then the community can/may have a look at it and
determine if it is a bug or not. Even if it turns out not to be a bug,
it will be nice to have it documented in the issue tracking system with
an explanation of why Derby behaves this way.
Jira (Derby's issue tracking system) can be accessed here:
https://issues.apache.org/jira/browse/DERBY
thanks,
--
Kristian
-Randy
Oystein Grovlen - Sun Norway wrote:
Randy Letness wrote:
I'm trying to debug a deadlock. There are two transactions: one
updates rows from table foo, and one selects the same rows from
table foo for reading. Is it possible to get in a deadlock in this
situation? I'm using the default READ_COMMITTED transaction
level. The transactions look like:
begin tx1 | begin tx2
select from foo | delete from foo
| insert into foo
| insert into foo
commit | commit
