org.apache.derby.impl.store.raw.xact

Class RowLocking1

java.lang.Object

org.apache.derby.impl.store.raw.xact.NoLocking

org.apache.derby.impl.store.raw.xact.RowLocking3

org.apache.derby.impl.store.raw.xact.RowLockingRR

org.apache.derby.impl.store.raw.xact.RowLocking2

org.apache.derby.impl.store.raw.xact.RowLocking1

All Implemented Interfaces:

LockingPolicy

public class RowLocking1
extends RowLocking2

A locking policy that implements row level locking with isolation degree 1. This is an implementation of Gray's degree 1 isolation, read uncommitted, or often referred to as dirty reads. Basically read operations are done with no locking. This locking policy is only to be used for read operations. The approach is to place all "write" container and row locks on the transaction group lock list. Locks on this group will last until end of transaction. This implementation will still get table level intent locks. This is to prevent hard cases where the container otherwise could be deleted while read uncommitted reader is still accessing it. In order to not get table level intent locks some sort of other ddl level lock would have to be implemented. All "read" row locks will be not be requested. Note that write operations extend from the RowLocking3 implementations.

See Also:

LockingPolicy

Field Summary

Fields inherited from class org.apache.derby.impl.store.raw.xact.RowLocking3

lf

Fields inherited from interface org.apache.derby.iapi.store.raw.LockingPolicy

MODE_CONTAINER, MODE_NONE, MODE_RECORD

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	RowLocking1(LockFactory lf)

Method Summary

Modifier and Type	Method and Description
boolean	lockRecordForRead(Transaction t, ContainerHandle container_handle, RecordHandle record, boolean waitForLock, boolean forUpdate) Obtain lock on record being read.
void	unlockRecordAfterRead(Transaction t, ContainerHandle container_handle, RecordHandle record, boolean forUpdate, boolean row_qualified) Unlock a record after it has been locked for read.

Methods inherited from class org.apache.derby.impl.store.raw.xact.RowLocking2

lockContainer, unlockContainer

Methods inherited from class org.apache.derby.impl.store.raw.xact.RowLockingRR

getReadLockType, getUpdateLockType, getWriteLockType

Methods inherited from class org.apache.derby.impl.store.raw.xact.RowLocking3

getMode, lockRecordForWrite, zeroDurationLockRecordForWrite

Methods inherited from class java.lang.Object

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

Constructor Detail

RowLocking1

protected RowLocking1(LockFactory lf)

Method Detail

lockRecordForRead

public boolean lockRecordForRead(Transaction t,
                                 ContainerHandle container_handle,
                                 RecordHandle record,
                                 boolean waitForLock,
                                 boolean forUpdate)
                          throws StandardException

Obtain lock on record being read.

Assumes that a table level IS has been acquired. Will acquire a Shared or Update lock on the row, depending on the "forUpdate" parameter.

Read lock will be placed on separate group from transaction.

Specified by:

lockRecordForRead in interface LockingPolicy

Overrides:

lockRecordForRead in class RowLocking2

Parameters:

t - The transaction to associate the lock with.

record - The record to be locked.

waitForLock - Should lock request wait until granted?

forUpdate - Whether to open for read or write access.

container_handle - Open Container used to get record. Will be used to row locks by the container they belong to.

Returns:

true if the lock was granted, false if waitForLock was false and the lock could not be granted.

Throws:

StandardException - Standard exception policy.

See Also:

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unlockRecordAfterRead

public void unlockRecordAfterRead(Transaction t,
                                  ContainerHandle container_handle,
                                  RecordHandle record,
                                  boolean forUpdate,
                                  boolean row_qualified)
                           throws StandardException

Description copied from class: RowLockingRR

Unlock a record after it has been locked for read.

In repeatable read only unlock records which "did not qualify". For example in a query like "select * from foo where a = 1" on a table with no index it is only necessary to hold locks on rows where a=1, but in the process of finding those rows the system will get locks on other rows to verify they are committed before applying the qualifier. Those locks can be released under repeatable read isolation.

Specified by:

unlockRecordAfterRead in interface LockingPolicy

Overrides:

unlockRecordAfterRead in class RowLocking2

Throws:

StandardException - Standard exception policy.

See Also:

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