If you are running against a MySQL database and upgrading Confluence from 1.0.x to 1.1.x, you may encounter the following error:

2004-06-29 11:09:11,052 ERROR [bucket.upgrade.UpgradeManager] Upgrade failed: Can't call commit when autocommit=true
java.sql.SQLException: Can't call commit when autocommit=true
at com.mysql.jdbc.Connection.commit(Connection.java:1175)
at org.apache.commons.dbcp.DelegatingConnection.commit(DelegatingConnection.java:248)
at org.apache.commons.dbcp.PoolingDataSource$PoolGuardConnectionWrapper.commit(PoolingDataSource.java:244)
at com.atlassian.confluence.upgrade.VersionedAttachmentDatabaseUpgradeTask.updateAttachmentsTable(VersionedAttachmentDatabaseUpgradeTask.java:71)
at com.atlassian.confluence.upgrade.VersionedAttachmentDatabaseUpgradeTask.doUpgrade(VersionedAttachmentDatabaseUpgradeTask.java:41)