com.sleepycat.je.txn

Class TxnChain

java.lang.Object

com.sleepycat.je.txn.TxnChain

public class TxnChain
extends Object

TxnChain supports "txn rollback", which undoes the write operations for a given txn to an arbitrary point. Txn rollback (and TxnChain construction) is done in 2 occasions: 1. During normal processing, when an ongoing txn must be rolled-back due to a syncup operation (see rep/txn/ReplayTxn.java). 2. During recovery, to process a "rollback period" (see RollbackTracker.java) In the JE log, the logrecs that make up a txn are chained, but each logrec contains undo info that refers to the pre-txn version of the associated record, which may not be the immediately previous version, if the txn writes the same record multiple times. For example, a log looks like this: lsn key data abortlsn 100 A 10 null_lsn (first instance of record A) 150 B 100 null_lsn (first instance of record B) ..... txn begins ..... 200 A 20 100 300 A deleted 100 400 B 200 150 500 A 30 100 600 C 10 null_lsn When reading the log, we can find all the records in the transaction. This chain exists: 500->400->300->200->null_lsn To rollback to an arbitrary entry in the transaction, we need a chain of all the records that occupied a given BIN slot during the transaction. chain. The key, data, and comparators are used to determine which records hash to the same slot, mimicking the btree itself. 300 400 500 600 | | | | \ / \ / \ / \ / 200 150 300 null_lsn revertToLsn true revertKD

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	TxnChain.CompareSlot Compare two keys using the appropriate comparator.
static class	TxnChain.RevertInfo

Constructor Summary

Constructors

Constructor and Description
TxnChain(long lastLoggedLsn, long txnId, long matchpoint, EnvironmentImpl envImpl)
TxnChain(long lastLoggedLsn, long txnId, long matchpoint, Map<DatabaseId,DatabaseImpl> undoDatabases, EnvironmentImpl envImpl)

Method Summary

Modifier and Type	Method and Description
VLSN	getLastValidVLSN()
Set<Long>	getRemainingLockedNodes() Returns LSNs for all nodes that should remain locked by the txn.
TxnChain.RevertInfo	pop() Return information about the next item on the transaction chain and remove it from the chain.
String	toString()

Methods inherited from class java.lang.Object

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

Constructor Detail

TxnChain

public TxnChain(long lastLoggedLsn,
                long txnId,
                long matchpoint,
                EnvironmentImpl envImpl)

TxnChain

public TxnChain(long lastLoggedLsn,
                long txnId,
                long matchpoint,
                Map<DatabaseId,DatabaseImpl> undoDatabases,
                EnvironmentImpl envImpl)
         throws DatabaseException

Throws:

DatabaseException

Method Detail

getRemainingLockedNodes

public Set<Long> getRemainingLockedNodes()

Returns LSNs for all nodes that should remain locked by the txn. Note that when multiple versions of a record were locked by the txn, the LSNs of all versions are returned. Only the latest version will actually be locked.

pop

public TxnChain.RevertInfo pop()

Return information about the next item on the transaction chain and remove it from the chain.

getLastValidVLSN

public VLSN getLastValidVLSN()

toString

public String toString()

Overrides:

toString in class Object