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Subject: svn commit: r688756 - in
 /db/derby/code/trunk/java/engine/org/apache/derby:
 iapi/services/locks/ iapi/sql/dictionary/ iapi/store/access/
 iapi/store/raw/ impl/store/access/ impl/store/raw/xact/
Date: Mon, 25 Aug 2008 15:28:36 -0000
To: derby-commits@db.apache.org
From: kahatlen@apache.org
Message-Id: <20080825152836.83893238896C@eris.apache.org>

Author: kahatlen
Date: Mon Aug 25 08:28:35 2008
New Revision: 688756

URL: http://svn.apache.org/viewvc?rev=688756&view=rev
Log:
DERBY-3693: Deadlocks accessing DB metadata

Added more detailed comments and cross references in the javadoc.

Modified:
    db/derby/code/trunk/java/engine/org/apache/derby/iapi/services/locks/LockOwner.java
    db/derby/code/trunk/java/engine/org/apache/derby/iapi/sql/dictionary/SPSDescriptor.java
    db/derby/code/trunk/java/engine/org/apache/derby/iapi/store/access/TransactionController.java
    db/derby/code/trunk/java/engine/org/apache/derby/iapi/store/raw/Transaction.java
    db/derby/code/trunk/java/engine/org/apache/derby/impl/store/access/RAMTransaction.java
    db/derby/code/trunk/java/engine/org/apache/derby/impl/store/raw/xact/Xact.java

Modified: db/derby/code/trunk/java/engine/org/apache/derby/iapi/services/locks/LockOwner.java
URL: http://svn.apache.org/viewvc/db/derby/code/trunk/java/engine/org/apache/derby/iapi/services/locks/LockOwner.java?rev=688756&r1=688755&r2=688756&view=diff
==============================================================================
--- db/derby/code/trunk/java/engine/org/apache/derby/iapi/services/locks/LockOwner.java (original)
+++ db/derby/code/trunk/java/engine/org/apache/derby/iapi/services/locks/LockOwner.java Mon Aug 25 08:28:35 2008
@@ -29,6 +29,24 @@
      * cannot be granted at once, even if {@code C_LockFactory.TIMED_WAIT}
      * was specified in the lock request.
      *
+     * <p>
+     *
+     * Normally, this method should return {@code false}, but in some very
+     * special cases it could be appropriate to return {@code true}. One
+     * example is when a stored prepared statement (SPS) is compiled and stored
+     * in a system table. In order to prevent exclusive locks in the system
+     * table from being held until the transaction that triggered the
+     * compilation is finished, the SPS will be compiled in a nested
+     * transaction that is committed and releases all locks upon completion.
+     * There is however a risk that the transaction that triggered the
+     * compilation is holding locks that the nested transaction needs, in
+     * which case the nested transaction will time out. The timeout will be
+     * detected by the calling code, and the operation will be retried in the
+     * parent transaction. To avoid long waits in the cases where the nested
+     * transaction runs into a lock conflict with its parent, the nested
+     * transaction's {@code LockOwner} instance could return {@code true} and
+     * thereby making it possible to detect lock conflicts instantly.
+     *
      * @return {@code true} if timed waits should time out immediately,
      * {@code false} otherwise
      */

Modified: db/derby/code/trunk/java/engine/org/apache/derby/iapi/sql/dictionary/SPSDescriptor.java
URL: http://svn.apache.org/viewvc/db/derby/code/trunk/java/engine/org/apache/derby/iapi/sql/dictionary/SPSDescriptor.java?rev=688756&r1=688755&r2=688756&view=diff
==============================================================================
--- db/derby/code/trunk/java/engine/org/apache/derby/iapi/sql/dictionary/SPSDescriptor.java (original)
+++ db/derby/code/trunk/java/engine/org/apache/derby/iapi/sql/dictionary/SPSDescriptor.java Mon Aug 25 08:28:35 2008
@@ -694,7 +694,11 @@
 					nestedTC = lcc.getTransactionCompile().startNestedUserTransaction(false);
                     // DERBY-3693: The nested transaction may run into a lock
                     // conflict with its parent transaction, in which case we
-                    // don't want to wait for a timeout.
+                    // don't want to wait for a timeout. If a lock timeout is
+                    // detected while we're executing the nested transaction,
+                    // we ignore the error and retry in the user transaction.
+                    // When retrying in the user transaction, we'll wait for
+                    // locks if necessary.
                     nestedTC.setNoLockWait(true);
 				}
 				catch (StandardException se)

Modified: db/derby/code/trunk/java/engine/org/apache/derby/iapi/store/access/TransactionController.java
URL: http://svn.apache.org/viewvc/db/derby/code/trunk/java/engine/org/apache/derby/iapi/store/access/TransactionController.java?rev=688756&r1=688755&r2=688756&view=diff
==============================================================================
--- db/derby/code/trunk/java/engine/org/apache/derby/iapi/store/access/TransactionController.java (original)
+++ db/derby/code/trunk/java/engine/org/apache/derby/iapi/store/access/TransactionController.java Mon Aug 25 08:28:35 2008
@@ -1483,10 +1483,17 @@
 
     /**
      * Tell this transaction whether it should time out immediately if a lock
-     * cannot be granted without waiting.
+     * cannot be granted without waiting. This mechanism can for instance be
+     * used if an operation is first attempted in a nested transaction to
+     * reduce the lifetime of locks held in the system tables (like when
+     * a stored prepared statement is compiled and stored). In such a case,
+     * the caller must catch timeout exceptions and retry the operation in the
+     * main transaction if a lock timeout occurs.
      *
      * @param noWait if {@code true} never wait for a lock in this transaction,
      * but time out immediately
+     * @see org.apache.derby.iapi.services.locks.LockOwner#noWait()
+     * @see org.apache.derby.iapi.store.raw.Transaction#setNoLockWait(boolean)
      */
     public void setNoLockWait(boolean noWait);
 

Modified: db/derby/code/trunk/java/engine/org/apache/derby/iapi/store/raw/Transaction.java
URL: http://svn.apache.org/viewvc/db/derby/code/trunk/java/engine/org/apache/derby/iapi/store/raw/Transaction.java?rev=688756&r1=688755&r2=688756&view=diff
==============================================================================
--- db/derby/code/trunk/java/engine/org/apache/derby/iapi/store/raw/Transaction.java (original)
+++ db/derby/code/trunk/java/engine/org/apache/derby/iapi/store/raw/Transaction.java Mon Aug 25 08:28:35 2008
@@ -61,10 +61,16 @@
 
     /**
      * Tell this transaction whether it should time out immediately if a lock
-     * cannot be granted without waiting.
+     * cannot be granted without waiting. This could be used in a nested
+     * transaction to prevent long waits if there is a lock conflict between
+     * the nested transaction and its parent. If it is used this way, the
+     * calling code should catch timeout exceptions from the nested transaction
+     * and retry the operation (without disabling waiting) in the parent
+     * transaction.
      *
      * @param noWait if {@code true} never wait for a lock in this transaction,
      * but time out immediately
+     * @see org.apache.derby.iapi.services.locks.LockOwner#noWait()
      */
     void setNoLockWait(boolean noWait);
 

Modified: db/derby/code/trunk/java/engine/org/apache/derby/impl/store/access/RAMTransaction.java
URL: http://svn.apache.org/viewvc/db/derby/code/trunk/java/engine/org/apache/derby/impl/store/access/RAMTransaction.java?rev=688756&r1=688755&r2=688756&view=diff
==============================================================================
--- db/derby/code/trunk/java/engine/org/apache/derby/impl/store/access/RAMTransaction.java (original)
+++ db/derby/code/trunk/java/engine/org/apache/derby/impl/store/access/RAMTransaction.java Mon Aug 25 08:28:35 2008
@@ -2436,17 +2436,13 @@
 	}
 
     /**
-     * Tell this transaction whether it should skip waiting for locks and
-     * instead time out immediately.
+     * {@inheritDoc}
      *
      * <p>
      *
      * For now, this only works if the transaction has its own compatibility
      * space. If it has inherited the compatibility space from its parent,
      * the request will be ignored (or cause a failure in debug builds).
-     *
-     * @param noWait if {@code true} never wait for a lock, but time out
-     * immediately
      */
     public void setNoLockWait(boolean noWait) {
         rawtran.setNoLockWait(noWait);

Modified: db/derby/code/trunk/java/engine/org/apache/derby/impl/store/raw/xact/Xact.java
URL: http://svn.apache.org/viewvc/db/derby/code/trunk/java/engine/org/apache/derby/impl/store/raw/xact/Xact.java?rev=688756&r1=688755&r2=688756&view=diff
==============================================================================
--- db/derby/code/trunk/java/engine/org/apache/derby/impl/store/raw/xact/Xact.java (original)
+++ db/derby/code/trunk/java/engine/org/apache/derby/impl/store/raw/xact/Xact.java Mon Aug 25 08:28:35 2008
@@ -584,8 +584,7 @@
     }
 
     /**
-     * Set whether lock requests should time out immediately if they can't be
-     * granted without waiting.
+     * {@inheritDoc}
      *
      * <p>
      *
@@ -593,9 +592,6 @@
      * space used in the request. If this transaction has inherited the
      * compatibility space from its parent, the call to this method has no
      * effect (except in debug builds, where an error will be raised).
-     *
-     * @param noWait whether lock requests should time out immediately if
-     * they can't be granted without waiting
      */
     public void setNoLockWait(boolean noWait) {
         if (SanityManager.DEBUG) {