/*
Derby - Class org.apache.derby.impl.store.access.btree.BTreePostCommit
Licensed to the Apache Software Foundation (ASF) under one or more
contributor license agreements. See the NOTICE file distributed with
this work for additional information regarding copyright ownership.
The ASF licenses this file to you under the Apache License, Version 2.0
(the "License"); you may not use this file except in compliance with
the License. You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/
package org.apache.derby.impl.store.access.btree;
import org.apache.derby.iapi.services.context.ContextManager;
import org.apache.derby.iapi.services.daemon.Serviceable;
import org.apache.derby.iapi.services.sanity.SanityManager;
import org.apache.derby.iapi.error.StandardException;
import org.apache.derby.iapi.store.access.AccessFactory;
import org.apache.derby.iapi.store.access.AccessFactoryGlobals;
import org.apache.derby.iapi.store.access.ConglomerateController;
import org.apache.derby.iapi.store.access.DynamicCompiledOpenConglomInfo;
import org.apache.derby.iapi.store.access.TransactionController;
import org.apache.derby.iapi.store.access.conglomerate.LogicalUndo;
import org.apache.derby.iapi.store.access.conglomerate.TransactionManager;
import org.apache.derby.iapi.store.raw.ContainerHandle;
import org.apache.derby.iapi.store.raw.FetchDescriptor;
import org.apache.derby.iapi.store.raw.LockingPolicy;
import org.apache.derby.iapi.store.raw.Page;
import org.apache.derby.iapi.store.raw.RecordHandle;
import org.apache.derby.iapi.types.DataValueDescriptor;
import org.apache.derby.iapi.reference.SQLState;
/**
The BTreePostCommit class implements the Serviceable protocol.
In it's role as a Serviceable object, it stores the state necessary to
find a page in a btree that may have committed delete's to reclaim.
In it's role as a PostCommitProcessor it looks up the page described, and
reclaims space in the btree. It first trys to clean up any deleted commits
on the page. It then will shrink the tree if it is going to delete all
rows from the page (RESOLVE - not done yet).
**/
class BTreePostCommit implements Serviceable
{
private AccessFactory access_factory = null;
private long page_number = ContainerHandle.INVALID_PAGE_NUMBER;
protected BTree btree = null;
/* Constructors for This class: */
BTreePostCommit(
AccessFactory access_factory,
BTree btree,
long input_page_number)
{
this.access_factory = access_factory;
this.btree = btree;
this.page_number = input_page_number;
}
/* Private/Protected methods of This class: */
/* Public Methods of This class: */
/* Public Methods of Serviceable class: */
/**
* The urgency of this post commit work.
* <p>
* This determines where this Serviceable is put in the post commit
* queue. Post commit work in the btree can be safely delayed until there
* is not user work to do.
*
* @return false, this work should not be serviced ASAP
**/
public boolean serviceASAP()
{
return(true);
}
// @return true, if this work needs to be done on a user thread immediately
public boolean serviceImmediately()
{
return false;
}
private final void doShrink(
OpenBTree open_btree,
DataValueDescriptor[] shrink_row)
throws StandardException
{
ControlRow root = null;
/*
System.out.println(
"Calling shrink on tree with levels = " +
open_btree.getHeight() + "\n");
*/
// Get the root page back, and perform a split following the
// to-be-inserted key. The split releases the root page latch.
root = ControlRow.get(open_btree, BTree.ROOTPAGEID);
root.shrinkFor(open_btree, shrink_row);
root = null;
// on return from shrinkFor the root pointer is invalid. The
// latch has been released, the root page may have changed from
// a branch to a leaf.
return;
}
/**
* perform the work described in the postcommit work.
* <p>
* In this implementation the only work that can be executed by this
* post commit processor is this class itself.
* <p>
*
* @return Returns Serviceable.DONE when work has completed, or
* returns Serviceable.REQUEUE if work needs to be requeued.
*
* @param contextMgr the context manager started by the
* post commit daemon
*
* @exception StandardException Standard exception policy.
**/
public int performWork(ContextManager contextMgr)
throws StandardException
{
// requeue if work was not completed in this try because of locks
boolean requeue_work = false;
TransactionManager tc = (TransactionManager)
this.access_factory.getAndNameTransaction(
contextMgr, AccessFactoryGlobals.SYS_TRANS_NAME);
TransactionManager internal_xact = tc.getInternalTransaction();
if (SanityManager.DEBUG)
{
if (SanityManager.DEBUG_ON("verbose_btree_post_commit"))
System.out.println("starting internal xact\n");
}
OpenBTree open_btree = new OpenBTree();
try
{
// Get lock on base table.
// The current space reclamation algorithm requires a table level
// lock on the btree - this is mostly because the shrink algorithm
// is not multi-user. This lock is requested NOWAIT as it does
// not want to impedede normal operation on the table. If the lock
// were to wait then the current lock manager livelock algorithm
// would block all subsequent lock requests on this btree even if
// they are compatible with the current holder of the lock.
//
// There are currently 3 outstanding enhancement requests:
// track 4237 - retry the work intelligently
// track 4238 - if can't get table lock, at least reclaim the rows
// track 4239 - do row level lock shrink - very hard to do.
//
ConglomerateController base_cc =
btree.lockTable(
internal_xact,
(ContainerHandle.MODE_FORUPDATE |
ContainerHandle.MODE_LOCK_NOWAIT),
TransactionController.MODE_TABLE,
TransactionController.ISOLATION_REPEATABLE_READ);
open_btree.init(
(TransactionManager) null,
internal_xact,
(ContainerHandle) null, // open the container
internal_xact.getRawStoreXact(),
false,
ContainerHandle.MODE_FORUPDATE,
TransactionController.MODE_TABLE,
btree.getBtreeLockingPolicy(
internal_xact.getRawStoreXact(),
TransactionController.MODE_TABLE,
LockingPolicy.MODE_CONTAINER,
TransactionController.ISOLATION_REPEATABLE_READ,
base_cc,
open_btree),
btree,
(LogicalUndo) null, // No logical undo necessry.
(DynamicCompiledOpenConglomInfo) null);
DataValueDescriptor[] shrink_key =
purgeCommittedDeletes(open_btree, this.page_number);
// RESOLVE (mikem) - move this call when doing row level locking.
if (shrink_key != null)
doShrink(open_btree, shrink_key);
open_btree.close();
}
catch (StandardException se)
{
//2 kinds of errors here expected here. Either container not found or dead lock.
// It is possible by the time this post commit work gets scheduled
// that the container has been dropped and that the open container
// call will return null - in this case just return assuming no
// work to be done.
//If it is a locking error, work is requeued. (4237)
if (se.getMessageId().equals(SQLState.LOCK_TIMEOUT) ||
se.getMessageId().equals(SQLState.DEADLOCK))
{
requeue_work = true;
}
//RESSOLVE-mike (4238) If you can't get a table level lock for btree space recovery in
//the post commit thread, maybe you should at least reclaim the
//rows on the page while you are at it. Use the same algorithm
//as exists in BTreeController.java. row level shrink is still a
//big problem and a separate track exists for it.
}
finally
{
internal_xact.commit();
internal_xact.destroy();
}
return(requeue_work ? Serviceable.REQUEUE : Serviceable.DONE);
}
private final DataValueDescriptor[] getShrinkKey(
OpenBTree open_btree,
ControlRow control_row,
int slot_no)
throws StandardException
{
DataValueDescriptor[] shrink_key =
open_btree.getConglomerate().createTemplate(
open_btree.getRawTran());
control_row.page.fetchFromSlot(
(RecordHandle) null,
slot_no, shrink_key,
(FetchDescriptor) null,
true);
return(shrink_key);
}
/**
* Reclaim space taken up by committed deleted rows.
* <p>
* This routine assumes it has been called by an internal transaction which
* has performed no work so far, and that it has an exclusive table lock.
* These assumptions mean that any deleted rows encountered must be from
* committed transactions (otherwise we could not have gotten the exclusive
* table lock).
* <p>
* RESOLVE (mikem) - under row locking this routine must do more work to
* determine a deleted row is a committed deleted row.
*
* @param open_btree The btree already opened.
* @param pageno The page number of the page to look for committed deletes.
*
* @exception StandardException Standard exception policy.
**/
private final DataValueDescriptor[] purgeCommittedDeletes(
OpenBTree open_btree,
long pageno)
throws StandardException
{
ControlRow control_row = null;
DataValueDescriptor[] shrink_key = null;
try
{
// The following can fail either if it can't get the latch or
// somehow the page requested no longer exists. In either case
// the post commit work will just skip it.
control_row = ControlRow.getNoWait(open_btree, pageno);
if (control_row != null)
{
Page page = control_row.page;
// The number records that can be reclaimed is:
// total recs - control row - recs_not_deleted
int num_possible_commit_delete =
page.recordCount() - 1 - page.nonDeletedRecordCount();
if (num_possible_commit_delete > 0)
{
// loop backward so that purges which affect the slot table
// don't affect the loop (ie. they only move records we
// have already looked at).
for (int slot_no = page.recordCount() - 1;
slot_no > 0;
slot_no--)
{
if (page.isDeletedAtSlot(slot_no))
{
if (page.recordCount() == 2)
{
// About to purge last row from page so
// remember the key so we can shrink the
// tree.
shrink_key = this.getShrinkKey(
open_btree, control_row, slot_no);
}
page.purgeAtSlot(slot_no, 1, true);
if (SanityManager.DEBUG)
{
if (SanityManager.DEBUG_ON(
"verbose_btree_post_commit"))
{
System.out.println(
"Purging row[" + slot_no + "]" +
"on page:" + pageno + ".\n");
}
}
}
}
}
if (page.recordCount() == 1)
{
if (SanityManager.DEBUG)
{
if (SanityManager.DEBUG_ON("verbose_btree_post_commit"))
{
System.out.println("Chance to shrink.\n");
}
}
}
}
else
{
if (SanityManager.DEBUG)
{
if (SanityManager.DEBUG_ON("verbose_btree_post_commit"))
{
System.out.println(
"Get No Wait returned null. page num = " + pageno +
"\n");
}
}
}
}
finally
{
if (control_row != null)
control_row.release();
}
return(shrink_key);
}
}