Possible bug with MVCC and schema creation.

Hi!

I've been diagnosing a couple of instances where our application seems to
deadlock when using HSQLDB (but is OK on other databases).

I think I now understand a secondary case when using MVCC. I'm using the
latest code from SVN.


When our app starts up, there is a thread responsible for creating the
database (if it doesn't exist). This amounts to the following occuring
(I've stripped it out to the calls that aren't relevant ):

One connection is created. It then does :
conn.setAutoCommit(false);

and nothing else.

Then a second connection is created (same thread). It attempts to then
start executing "CREATE TABLE" functions. However - it deadlocks on the
first statement and never returns.
If the first connection is not created, everything works fine.

This seems to be because of the following:

TransactionManagerMVCC::beginActionTPL, line 935 does an
'cs.isCatalogLock()' which is true, since the statement is a DDL statement.

It then (lines 942+) finds all the other sessions (which is the other
session), and calls setWaitingSessionTPL(session). This ends by calling

session.latch.setCount(count);

On the current session. Then, later on, line 1319 of Session.java, there is
a latch.await() which now waits forever.

I obviously don't understand the code enough to be able to determine what's
going wrong here. I can re-write things to avoid having the concurrent
connection, but I'm fairly sure my other deadlocks are similar situations,
which probably means a statement has deemed to require a catalog lock, and
there's something blocking it (which may be a totally idle connection in a
dbcp connection pool).

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