com.sleepycat.je.rep.txn

Class ReadonlyTxn

java.lang.Object

com.sleepycat.je.txn.Locker

com.sleepycat.je.txn.Txn

com.sleepycat.je.rep.txn.ReadonlyTxn

All Implemented Interfaces:

Loggable, VersionedWriteLoggable

public class ReadonlyTxn
extends Txn

A ReadonlyTxn represents - a user initiated Txn executed on the Master node, when local-write or read-only is configured, or - a user initiated Txn executed on the Replica node, whether or not local-write is configured, or - an auto-commit Txn on a Replica node for a replicated DB. As its name implies it is used to implement the read-only semantics for access to replicated DBs on the Replica. It is not replicated txn, i.e., it is not part of the rep stream. In addition, it uses the transaction hooks defined on Txn to implement the ReplicaConsistencyPolicy. This must be done for all access to replicated DBs, including when local-write is configured.

Field Summary

Fields inherited from class com.sleepycat.je.txn.Txn

ACCUMULATED_LIMIT, commitLsn, dbCleanupSet, firstLoggedLsn, lastLoggedLsn, openedDatabaseHandles, repContext, undoDatabases

Fields inherited from class com.sleepycat.je.txn.Locker

afterWaiterHook, envImpl, id, lockManager, thread

Constructor Summary

Constructors

Constructor and Description
ReadonlyTxn(EnvironmentImpl envImpl, TransactionConfig config)

Method Summary

Modifier and Type	Method and Description
void	disallowReplicaWrite() Unconditionally throws ReplicaWriteException because this locker was created on a replica.
boolean	isLocalWrite() Returns true if writes may only be to non-replicated DBs using this locker, or false if writes may only be to replicated DBs.
LockResult	lockInternal(long lsn, LockType lockType, boolean noWait, boolean jumpAheadOfWaiters, DatabaseImpl database) Provides a wrapper to screen for write locks.
void	preLogWithoutLock(DatabaseImpl database) If logging occurs before locking, we must screen out write locks here.
protected void	txnBeginHook(TransactionConfig config) Verifies that consistency requirements are met before allowing the transaction to proceed.

Methods inherited from class com.sleepycat.je.txn.Txn

abort, abort, abort, addDbCleanup, addLock, addLogInfo, addOpenedDatabase, checkIfFrozen, checkPreempted, checkState, cleanupDatabaseImpls, clearReadLocks, clearWriteLocks, close, collectStats, commit, commit, commit, createAutoTxn, createLocalAutoTxn, createLocalTxn, dumpLog, generateId, getCommitDurability, getCommitToken, getDbCleanupSet, getDefaultDurability, getDTVLSN, getEmbeddedLoggables, getEnvironmentImpl, getExplicitDurabilityConfigured, getExplicitSyncConfigured, getFirstActiveLsn, getImportunate, getLastFormatChange, getLastLsn, getLogSize, getLogSize, getPrepared, getReadLockIds, getReplicatorNodeId, getState, getTransaction, getTransactionId, getTriggerDbs, getTxnLocker, getUndoDatabases, getWriteLockIds, getWriteLockInfo, hasReplicationFormat, isAutoTxn, isClosed, isMasterTxn, isOnlyAbortable, isReadCommittedIsolation, isReadOnly, isReplicationFormatWorthwhile, isRolledBack, isSerializableIsolation, isSuspended, isTransactional, isValid, lockingRequired, logicalEquals, newNonTxnLocker, nonTxnOperationEnd, noteTriggerDb, operationEnd, postLogAbortHook, postLogCommitAbortHook, postLogCommitHook, preLogAbortHook, preLogCommitHook, prepare, propagatePostCommitException, readFromLog, registerCursor, registerImmediately, releaseNonTxnLocks, releaseWriteLocks, removeLock, setDbCleanupState, setImportunate, setOnlyAbortable, setPrepared, setRollback, setSuspended, setTransaction, undo, unRegisterCursor, updateLoggedForTxn, writeToLog, writeToLog

Methods inherited from class com.sleepycat.je.txn.Locker

addDeleteInfo, allowReleaseLockAfterLsnChange, demoteLock, dumpLockTable, getDefaultNoWait, getEnvironment, getId, getInitialLockTimeout, getLockTimeout, getPreemptable, getTxnTimeout, isReadUncommittedDefault, isReplicated, isTimedOut, lock, lockAfterLsnChange, nonBlockingLock, openCursorHook, operationEnd, operationEnd, releaseLock, setClosingLocker, setDefaultNoWait, setLockTimeout, setPreemptable, setPreempted, setTxnTimeout, sharesLocksWith, toString

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

ReadonlyTxn

public ReadonlyTxn(EnvironmentImpl envImpl,
                   TransactionConfig config)
            throws DatabaseException

Throws:

DatabaseException

Method Detail

isLocalWrite

public boolean isLocalWrite()

Description copied from class: Locker

Returns true if writes may only be to non-replicated DBs using this locker, or false if writes may only be to replicated DBs. By default (this implementation) local-write is true, since it is allowed for all non-txnal lockers and for all lockers in a standalone environment. This method is overridden and returns false for for user transactions in a replicated environment that are not explicitly configured for local-write. This method is used to describe a locker's configured usage for checking the validity of an API write operation. This is checked by Cursor methods at the beginning of each write operation.

Overrides:

isLocalWrite in class Locker

lockInternal

public LockResult lockInternal(long lsn,
                               LockType lockType,
                               boolean noWait,
                               boolean jumpAheadOfWaiters,
                               DatabaseImpl database)
                        throws LockNotAvailableException,
                               LockConflictException,
                               DatabaseException

Provides a wrapper to screen for write locks. The use of write locks is used to infer that an attempt is being made to modify a replicated database. Note that this technique misses "conditional" updates, for example a delete operation using a non-existent key, but we are ok with that since the primary intent here is to ensure the integrity of the replicated stream that is being played back at that replica and these checks prevent such mishaps.

Overrides:

lockInternal in class Txn

Parameters:

lsn - is the node to lock.

lockType - is the type of lock to request.

noWait - is true to override the defaultNoWait setting. If true, or if defaultNoWait is true, throws LockNotAvailableException if the lock cannot be granted without waiting.

jumpAheadOfWaiters - grant the lock before other waiters, if any.

database - is the database containing lsn.

Throws:

LockConflictException - if a blocking lock could not be acquired.

LockNotAvailableException

DatabaseException

See Also:

Locker.lockInternal(long, com.sleepycat.je.txn.LockType, boolean, boolean, com.sleepycat.je.dbi.DatabaseImpl)

preLogWithoutLock

public void preLogWithoutLock(DatabaseImpl database)

If logging occurs before locking, we must screen out write locks here. If we allow the operation (e.g., for a NameLN), then be sure to call the base class method to prepare to undo in the (very unlikely) event that logging succeeds but locking fails. [#22875]

Overrides:

preLogWithoutLock in class Txn

disallowReplicaWrite

public void disallowReplicaWrite()

Unconditionally throws ReplicaWriteException because this locker was created on a replica.

Overrides:

disallowReplicaWrite in class Locker

txnBeginHook

protected void txnBeginHook(TransactionConfig config)
                     throws ReplicaConsistencyException,
                            DatabaseException

Verifies that consistency requirements are met before allowing the transaction to proceed.

Overrides:

txnBeginHook in class Txn

Parameters:

config - the transaction config that applies to the txn

Throws:

DatabaseException - if there is a failure

ReplicaConsistencyException