Class TransactionTable

java.lang.Object
org.apache.derby.impl.store.raw.xact.TransactionTable
All Implemented Interfaces:
Externalizable, Serializable, Formatable, TypedFormat

public class TransactionTable extends Object implements Formatable
The transaction table is used by the transaction factory to keep track of all transactions that are in the system.
The transction table serves the following purposes:
  1. checkpoint - when a checkpoint log record is written out, it writes out also all transactions that have updated the database. RESOLVE: this is actually not used right now - rather, the transaction table is reconstructed during the redo phase by traversing from the undo LWM. It is a goal to use this transaction table (and traversing from the redoLWM) instead of rebuilding it to speed up recovery.
  2. Quiesce State - when a system enters the quiesce state, it needs to account for all transactions in the system, even those which are just started and are in their IDLE state.
  3. TransactionTable VTI - we need to get a snapshot of all transactions in the system for diagnostic purposes.
In order to speed up the time it takes to look up a transaction from the transaction table, each transaction must have a unique transaction Id. This means newly coined transaction must also have a transaction Id.

During recovery, there is only one real xact object doing all the recovery work, but there could be many outstanding transactions that are gleamed from the log. Each of these "recovery transactions" have its on entry into the transaction table but they all share the same Xact object.

Multithreading considerations:
TransactionTable must be MT-safe it is called upon by many threads simultaneously (except during recovery)

Methods that are only called during recovery don't need to take MT considerations, and can safely use iterators with no additional synchronization.

See Also:
  • Field Details

  • Constructor Details

    • TransactionTable

      public TransactionTable()
      MT - not needed for constructor
  • Method Details

    • findTransactionEntry

      private TransactionTableEntry findTransactionEntry(TransactionId id)
      generic methods called by all clients of transaction table Must be MT -safe
    • visitEntries

      void visitEntries(TransactionTable.EntryVisitor visitor)

      Visit all the entries in the transaction table.

      MT - MT safe

      Entries that are added to or removed from the transaction table while it's being traversed, may or may not be visited. All the entries that are present in the map when this method is called, and have not been removed when the method returns, will have been visited exactly once (except if the visit() method returns false before all entries have been visited, in which case the traversal of the map will stop earlier).

      Note however that this method does not guarantee that a single TransactionTableEntry is not accessed concurrently by multiple threads. If the visitor accesses some of the entry's mutable state, the caller must ensure that appropriate synchronization protection is in place. For example, if accessing the update state of the entry, the caller must synchronize on "this" (the TransactionTable instance).

      Parameters:
      visitor - the visitor to apply on each transaction table entry
    • add

      void add(Xact xact, boolean exclude)
    • remove

      boolean remove(TransactionId id)
      remove the transaction Id an return false iff the transaction is found in the table and it doesn't need exclusion during quiesce state
    • addUpdateTransaction

      public void addUpdateTransaction(TransactionId tid, RawTransaction tran, int transactionStatus)
      Change a transaction to update or add an update transaction to this table.
      Parameters:
      tid - the transaction id
      tran - the transaction to be added
      transactionStatus - the transaction status that is stored in the BeginXact log record
    • removeUpdateTransaction

      void removeUpdateTransaction(TransactionId id)
      Change update transaction to non-update

      MT - MT safe, since vector is MT-safe.

      Parameters:
      id - the transaction Id
    • prepareTransaction

      void prepareTransaction(TransactionId id)
      Change transaction to prepared.

      MT - unsafe, caller is recovery, which is single threaded.

      Parameters:
      id - the transaction Id
    • findTransactionContextByGlobalId

      public ContextManager findTransactionContextByGlobalId(GlobalXactId global_id)
      Find a transaction in the table by Global transaction id.

      This routine use to be only called during offline recovery so performance was not critical. Since that time more calls have been made, including one in startGlobalTransaction() so a linear search may no longer be appropriate. See DERBY-828.

      Parameters:
      global_id - The global transaction we are searching for.
      Returns:
      The ContextManager of the transaction being searched for.
    • hasActiveUpdateTransaction

      boolean hasActiveUpdateTransaction()
      Return true if there is no transaction actively updating the database. New transaction may be started or old transaction committed right afterward, the caller of this routine must have other ways to stop transactions from starting or ending.

      MT - safe

    • getTypeFormatId

      public int getTypeFormatId()
      Return my format identifier.
      Specified by:
      getTypeFormatId in interface TypedFormat
      Returns:
      The identifier. (A UUID stuffed in an array of 16 bytes).
    • writeExternal

      public void writeExternal(ObjectOutput out) throws IOException
      Specified by:
      writeExternal in interface Externalizable
      Throws:
      IOException - problem reading the transaction table
    • readExternal

      public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException
      Specified by:
      readExternal in interface Externalizable
      Throws:
      IOException - problem reading the transaction table
      ClassNotFoundException - problem reading the transaction table
    • largestUpdateXactId

      public TransactionId largestUpdateXactId()
      Return the largest update transactionId I have seen so far.

      MT - unsafe, caller is recovery, which is single threaded.

    • hasRollbackFirstTransaction

      public boolean hasRollbackFirstTransaction()
      Is there an active internal transaction in the transaction table.

      MT - unsafe, caller is recovery, which is single threaded.

    • hasPreparedRecoveredXact

      public boolean hasPreparedRecoveredXact()
      Is there a prepared transaction that are recovered durring the recovery in the transaction table.

      MT - unsafe, caller is recovery, which is single threaded.

    • hasPreparedXact

      public boolean hasPreparedXact()
      Is there a prepared transaction in the transaction table.

      MT - unsafe, called during boot, which is single threaded.

    • hasPreparedXact

      private boolean hasPreparedXact(boolean recovered)
      Is there a prepared transaction in the transaction table.

      MT - unsafe, caller is recovery/at boot, which is single threaded.

      Parameters:
      recovered - true to search for transaction that are in prepared during recovery. recovered tranaction. false > to search for just prepared transactons.
      Returns:
      true if there is a prepared transaction and recovered when recovered argument is true
    • getMostRecentRollbackFirstTransaction

      public boolean getMostRecentRollbackFirstTransaction(RawTransaction tran)
      Get the most recently added transaction that says it needs to be rolled back first (an InternalXact) from the transaction table and make the passed in transaction assume its identity. Should only be used in recovery undo !! RESOLVE: (sku)I don't think even these internal transactions need to be rolled back in the reverse order, because they are physical in nature. But it won't hurt.

      MT - unsafe, caller is recovery, which is single threaded.

    • getMostRecentTransactionForRollback

      public boolean getMostRecentTransactionForRollback(RawTransaction tran)
      Get the most recently non-prepared added transaction from the transaction table and make the passed in transaction assume its identity. Prepared transactions will not be undone. RESOLVE: (sku) I don't think normal user transactions needs to be rolled back in order, but it won't hurt. Should only be used in recovery undo !!

      MT - unsafe, caller is recovery, which is single threaded.

    • getMostRecentPreparedRecoveredXact

      public boolean getMostRecentPreparedRecoveredXact(RawTransaction tran)
      Get the most recent recovered prepared transaction.

      Get the most recently added transaction that says it is prepared during recovery the transaction table and make the passed in transaction assume its identity.

      This routine, unlike the redo and rollback getMostRecent*() routines expects a brand new transaction to be passed in. If a candidate transaction is found, then upon return the transaction table will be altered such that the old entry no longer exists, and a new entry will exist pointing to the transaction passed in. The new entry will look the same as if the prepared transaction had been created during runtime rather than recovery. Should only be used in recovery handle prepare after undo !!

      MT - unsafe, caller is recovery, which is single threaded.

      Parameters:
      tran - Newly allocated transaction to add to link to a entry.
      Returns:
      true if a candidate transaction has been found. false if no prepared/recovery transactions found in the table.
    • getFirstLogInstant

      public LogInstant getFirstLogInstant()
      Get the least recently added (oldest) transaction
      Returns:
      the RawTransaction's first log instant

      MT - safe, caller can be recovery or checkpoint

    • findAndAssumeTransaction

      boolean findAndAssumeTransaction(TransactionId id, RawTransaction tran)
      Find a transaction using the transaction id, and make the passed in transaction assume the identity and properties of that transaction.

      MT - unsafe, caller is recovery, which is single threaded.

      Parameters:
      id - transaction Id
      tran - the transaction that was made to assume the transactionID and all other relevant information stored in the transaction table
      Returns:
      true if transaction can be found, false otherwise
    • getTransactionInfo

      public TransactionInfo[] getTransactionInfo()
      Get a printable version of the transaction table
    • toString

      public String toString()
      Overrides:
      toString in class Object