Package bitronix.tm.journal

Class TransactionLogRecord

java.lang.Object
bitronix.tm.journal.TransactionLogRecord
public class TransactionLogRecord extends Object
Representation of a transaction log record on disk.

On-disk format has been implemented following Mike Spille's recommendations. Quoting him:

[RECORD_TYPE :4] [RECORD_LEN :4] [HEADER_LEN :4] [System.currentTimeMillis :8] [Sequence number :4] [Checksum :4] [Payload :X] [END_RECORD_INDICATOR :4]

Where [RECORD_TYPE] is a passed-in record type from the TM. [RECORD_LEN] is the overall record length (sans [RECORD_TYPE and [RECORD_LEN]). [HEADER_LEN] is the length of the remainder of the header - important if you want to support easy upgrades of your format. The remaining pieces are the rest of the header, and the payload. The header at least should have [System.currentTimeMillis] and [Sequence number], with the [sequence number] coming from some monotically increasing sequence generator unique to the process. The [checksum] is optional for the paranoid among us. The time information can be very useful for profiling and tracking down problems in production, and in conjunction with the sequence number it can give you precise ordering. This doesn't give you much in this solution, but can be priceless if you ever move to a system with multiple dual log file pairs to lessen single-threading on a single log file pair. Finally, I like having an [END_RECORD_INDICATOR] as an extra corruption detector device - I'm a suspenders and belt kind of guy. Actually, the END_RECORD_INDICATOR and [RECORD_LEN] in conjunction are very useful in development, as well, to catch programming mistakes in the log system early.

Payload contains [GTRID LENGTH :1] [GTRID :A] [UNIQUE NAMES COUNT :4] ([UNIQUE NAME LENGTH :2] [UNIQUE NAME :Y] ...) which makes a major difference with Mike's proposed format because here a record can vary in length: the GTRID size is A bytes long (A being the GTRID length) and there can be X unique names that are Y characters long, Y being eventually different for each name.

Author:
lorban
See Also:

  • Constructor Details

    • TransactionLogRecord

      public TransactionLogRecord(int status, int recordLength, int headerLength, long time, int sequenceNumber, int crc32, Uid gtrid, Set<String> uniqueNames, int endRecord)
      Use this constructor when restoring a log from the disk.
      Parameters:
      status - record type
      recordLength - record length excluding status and recordLength
      headerLength - length of all fields except gtrid, uniqueNames and endRecord
      time - current time in milliseconds
      sequenceNumber - atomically generated sequence number during a JVM's lifespan
      crc32 - checksum of the full record
      gtrid - global transaction id
      uniqueNames - unique names of XA data sources used in this transaction
      endRecord - end of record marker

    • TransactionLogRecord

      public TransactionLogRecord(int status, Uid gtrid, Set<String> uniqueNames)
      Create a new transaction log ready to be stored.
      Parameters:
      status - record type
      gtrid - global transaction id
      uniqueNames - unique names of XA data sources used in this transaction

  • Method Details

    • getStatus

      public int getStatus()

    • getRecordLength

      public int getRecordLength()

    • getHeaderLength

      public int getHeaderLength()

    • getTime

      public long getTime()

    • getSequenceNumber

      public int getSequenceNumber()

    • getCrc32

      public int getCrc32()

    • getGtrid

      public Uid getGtrid()

    • getUniqueNames

      public Set<String> getUniqueNames()

    • getEndRecord

      public int getEndRecord()

    • isCrc32Correct

      public boolean isCrc32Correct()
      Recalculate the CRC32 value of this record (using calculateCrc32()) and compare it with the stored value.
      Returns:
      true if the recalculated value equals the stored one, false otherwise.

    • calculateCrc32

      public int calculateCrc32()
      Calculate the CRC32 value of this record.
      Returns:
      the CRC32 value of this record.

    • toString

      public String toString()
      Overrides:
      toString in class Object